Android源码分析--MediaServer源码分析（二）
2024-05-10 16:44:04
在上一篇博客中Android源码分析–MediaServer源码分析（一），我们知道了ProcessState和defaultServiceManager，在分析源码的过程中，我们被Android的Binder通信机制中的各种复杂的类关系搞的眼花缭乱，接下来我们就以MediaPlayerService为例来分析一下Binder的通信机制。首先来回顾一下：
- BpBinder和BBinder都是Android中Binder通信的代表类，其中BpBinder是客户端用来与Server交互的代理类，p代表的就是proxy，而BBinder则是交互的目的端；
- BpBinder和BBinder是相互对应的，Binder系统会通过handle来标识对应的BBinder。
Android的通信机制基本上可以看做是Client、Server和ServiceManager三者之间的交互：
- Server首先要注册一些Service到ServiceManager；
- 如果某个Client要使用Service，则首先到ServiceManager中获得该Service的相关信息；
- Client得到Service信息，然后和该Service所在的Server进程建立通信之后使用Service。
注册MediaPlayerService
我们知道若要使用一个Service的话首先要进行注册，所有首先让我们来看看MediaService是如何注册的，文件位置：frameworks\base\media\libmediaplayerservice\MediaPlayerService.cpp
<code class="hljs coffeescript has-numbering" style="display: block; padding: 0px; color: inherit; box-sizing: border-box; font-family: 'Source Code Pro', monospace;font-size:undefined; white-space: pre; border-radius: 0px; word-wrap: normal; background: transparent;"><span class="hljs-reserved" style="box-sizing: border-box;">void</span> <span class="hljs-attribute" style="box-sizing: border-box; color: rgb(0, 136, 0);">MediaPlayerService</span>::instantiate() {defaultServiceManager<span class="hljs-function" style="box-sizing: border-box;"><span class="hljs-params" style="color: rgb(102, 0, 102); box-sizing: border-box;">()</span>-></span>addService(String16(<span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"media.player"</span>), <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">new</span> MediaPlayerService());
}</code><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right; background-color: rgb(238, 238, 238);"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li><li style="box-sizing: border-box; padding: 0px 5px;">4</li></ul><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right; background-color: rgb(238, 238, 238);"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li><li style="box-sizing: border-box; padding: 0px 5px;">4</li></ul>
defaultServiceManager返回的其实是一个BpServiceManager对象，在这里我看到了注册的函数addService：
<code class="hljs haskell has-numbering" style="display: block; padding: 0px; color: inherit; box-sizing: border-box; font-family: 'Source Code Pro', monospace;font-size:undefined; white-space: pre; border-radius: 0px; word-wrap: normal; background: transparent;"> virtual status_t addService(const <span class="hljs-type" style="box-sizing: border-box; color: rgb(102, 0, 102);">String16</span>& name, const sp<<span class="hljs-type" style="box-sizing: border-box; color: rgb(102, 0, 102);">IBinder</span>>& service){<span class="hljs-type" style="box-sizing: border-box; color: rgb(102, 0, 102);">Parcel</span> <span class="hljs-typedef" style="box-sizing: border-box;"><span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">data</span>, reply;</span>//将<span class="hljs-type" style="box-sizing: border-box; color: rgb(102, 0, 102);">Descriptor</span>作为令牌<span class="hljs-typedef" style="box-sizing: border-box;"><span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">data</span>.writeInterfaceToken<span class="hljs-container" style="box-sizing: border-box;">(<span class="hljs-type" style="box-sizing: border-box; color: rgb(102, 0, 102);">IServiceManager</span>::<span class="hljs-title" style="box-sizing: border-box;">getInterfaceDescriptor</span>()</span>);</span><span class="hljs-typedef" style="box-sizing: border-box;"><span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">data</span>.writeString16<span class="hljs-container" style="box-sizing: border-box;">(<span class="hljs-title" style="box-sizing: border-box;">name</span>)</span>;</span><span class="hljs-typedef" style="box-sizing: border-box;"><span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">data</span>.writeStrongBinder<span class="hljs-container" style="box-sizing: border-box;">(<span class="hljs-title" style="box-sizing: border-box;">service</span>)</span>;</span>status_t err = remote()->transact(<span class="hljs-type" style="box-sizing: border-box; color: rgb(102, 0, 102);">ADD_SERVICE_TRANSACTION</span>, <span class="hljs-typedef" style="box-sizing: border-box;"><span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">data</span>, &reply);</span>return err == <span class="hljs-type" style="box-sizing: border-box; color: rgb(102, 0, 102);">NO_ERROR</span> ? reply.readExceptionCode() : err;
}</code><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right; background-color: rgb(238, 238, 238);"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li><li style="box-sizing: border-box; padding: 0px 5px;">4</li><li style="box-sizing: border-box; padding: 0px 5px;">5</li><li style="box-sizing: border-box; padding: 0px 5px;">6</li><li style="box-sizing: border-box; padding: 0px 5px;">7</li><li style="box-sizing: border-box; padding: 0px 5px;">8</li><li style="box-sizing: border-box; padding: 0px 5px;">9</li><li style="box-sizing: border-box; padding: 0px 5px;">10</li></ul><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right; background-color: rgb(238, 238, 238);"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li><li style="box-sizing: border-box; padding: 0px 5px;">4</li><li style="box-sizing: border-box; padding: 0px 5px;">5</li><li style="box-sizing: border-box; padding: 0px 5px;">6</li><li style="box-sizing: border-box; padding: 0px 5px;">7</li><li style="box-sizing: border-box; padding: 0px 5px;">8</li><li style="box-sizing: border-box; padding: 0px 5px;">9</li><li style="box-sizing: border-box; padding: 0px 5px;">10</li></ul>
Parcel类可以看作一个数据块，在该类的内部主要封装了一些数据操作的方法。在写入数据之后remote()->transact方法，remote()方法返回的值是mRemote，在上一篇中我们知道它是一个BpBinder对象，之后我们的通信工作就交由了BpBinder的transact方法：
<code class="hljs lasso has-numbering" style="display: block; padding: 0px; color: inherit; box-sizing: border-box; font-family: 'Source Code Pro', monospace;font-size:undefined; white-space: pre; border-radius: 0px; word-wrap: normal; background: transparent;">status_t BpBinder<span class="hljs-tag" style="color: rgb(0, 102, 102); box-sizing: border-box;">::transact</span>(uint32_t code, const Parcel<span class="hljs-subst" style="color: rgb(0, 0, 0); box-sizing: border-box;">&</span> <span class="hljs-built_in" style="color: rgb(102, 0, 102); box-sizing: border-box;">data</span>, Parcel<span class="hljs-subst" style="color: rgb(0, 0, 0); box-sizing: border-box;">*</span> reply, uint32_t flags)
{<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">// Binder一旦死去将永远不能复活.</span><span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">if</span> (mAlive) {status_t status <span class="hljs-subst" style="color: rgb(0, 0, 0); box-sizing: border-box;">=</span> IPCThreadState<span class="hljs-tag" style="color: rgb(0, 102, 102); box-sizing: border-box;">::self</span>()<span class="hljs-subst" style="color: rgb(0, 0, 0); box-sizing: border-box;">-></span>transact(mHandle, code, <span class="hljs-built_in" style="color: rgb(102, 0, 102); box-sizing: border-box;">data</span>, reply, flags);<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">if</span> (status <span class="hljs-subst" style="color: rgb(0, 0, 0); box-sizing: border-box;">==</span> DEAD_OBJECT) mAlive <span class="hljs-subst" style="color: rgb(0, 0, 0); box-sizing: border-box;">=</span> <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">0</span>;<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">return</span> status;}<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">return</span> DEAD_OBJECT;
}</code><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right; background-color: rgb(238, 238, 238);"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li><li style="box-sizing: border-box; padding: 0px 5px;">4</li><li style="box-sizing: border-box; padding: 0px 5px;">5</li><li style="box-sizing: border-box; padding: 0px 5px;">6</li><li style="box-sizing: border-box; padding: 0px 5px;">7</li><li style="box-sizing: border-box; padding: 0px 5px;">8</li><li style="box-sizing: border-box; padding: 0px 5px;">9</li><li style="box-sizing: border-box; padding: 0px 5px;">10</li><li style="box-sizing: border-box; padding: 0px 5px;">11</li><li style="box-sizing: border-box; padding: 0px 5px;">12</li><li style="box-sizing: border-box; padding: 0px 5px;">13</li></ul><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right; background-color: rgb(238, 238, 238);"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li><li style="box-sizing: border-box; padding: 0px 5px;">4</li><li style="box-sizing: border-box; padding: 0px 5px;">5</li><li style="box-sizing: border-box; padding: 0px 5px;">6</li><li style="box-sizing: border-box; padding: 0px 5px;">7</li><li style="box-sizing: border-box; padding: 0px 5px;">8</li><li style="box-sizing: border-box; padding: 0px 5px;">9</li><li style="box-sizing: border-box; padding: 0px 5px;">10</li><li style="box-sizing: border-box; padding: 0px 5px;">11</li><li style="box-sizing: border-box; padding: 0px 5px;">12</li><li style="box-sizing: border-box; padding: 0px 5px;">13</li></ul>
BpBinder完全将工作交给了IPCThreadState，接下来的任务也全部转移到了IPCThreadState类中。
IPCThreadState类分析
IPCThreadState也是以单例模式设计的。由于每个进程只维护了一个ProcessState实例，同时ProcessState只启动一个 Pool thread，也就是说每一个进程只会启动一个Pool thread，因此每个进程则只需要一个IPCThreadState即可。首先让我们来看看这个self方法，文件位置：frameworks\base\libs\binder\IPCThreadState.cpp
<code class="hljs php has-numbering" style="display: block; padding: 0px; color: inherit; box-sizing: border-box; font-family: 'Source Code Pro', monospace;font-size:undefined; white-space: pre; border-radius: 0px; word-wrap: normal; background: transparent;">IPCThreadState* IPCThreadState::<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">self</span>()
{<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">if</span> (gHaveTLS) {
restart:<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">const</span> pthread_key_t k = gTLS;IPCThreadState* st = (IPCThreadState*)pthread_getspecific(k);<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">if</span> (st) <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">return</span> st;<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">return</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">new</span> IPCThreadState;}<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">if</span> (gShutdown) <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">return</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">NULL</span>;pthread_mutex_lock(&gTLSMutex);<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">if</span> (!gHaveTLS) {<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">if</span> (pthread_key_create(&gTLS, threadDestructor) != <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">0</span>) {pthread_mutex_unlock(&gTLSMutex);<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">return</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">NULL</span>;}gHaveTLS = <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">true</span>;}pthread_mutex_unlock(&gTLSMutex);<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">goto</span> restart;
}</code><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right; background-color: rgb(238, 238, 238);"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li><li style="box-sizing: border-box; padding: 0px 5px;">4</li><li style="box-sizing: border-box; padding: 0px 5px;">5</li><li style="box-sizing: border-box; padding: 0px 5px;">6</li><li style="box-sizing: border-box; padding: 0px 5px;">7</li><li style="box-sizing: border-box; padding: 0px 5px;">8</li><li style="box-sizing: border-box; padding: 0px 5px;">9</li><li style="box-sizing: border-box; padding: 0px 5px;">10</li><li style="box-sizing: border-box; padding: 0px 5px;">11</li><li style="box-sizing: border-box; padding: 0px 5px;">12</li><li style="box-sizing: border-box; padding: 0px 5px;">13</li><li style="box-sizing: border-box; padding: 0px 5px;">14</li><li style="box-sizing: border-box; padding: 0px 5px;">15</li><li style="box-sizing: border-box; padding: 0px 5px;">16</li><li style="box-sizing: border-box; padding: 0px 5px;">17</li><li style="box-sizing: border-box; padding: 0px 5px;">18</li><li style="box-sizing: border-box; padding: 0px 5px;">19</li><li style="box-sizing: border-box; padding: 0px 5px;">20</li><li style="box-sizing: border-box; padding: 0px 5px;">21</li><li style="box-sizing: border-box; padding: 0px 5px;">22</li><li style="box-sizing: border-box; padding: 0px 5px;">23</li></ul><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right; background-color: rgb(238, 238, 238);"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li><li style="box-sizing: border-box; padding: 0px 5px;">4</li><li style="box-sizing: border-box; padding: 0px 5px;">5</li><li style="box-sizing: border-box; padding: 0px 5px;">6</li><li style="box-sizing: border-box; padding: 0px 5px;">7</li><li style="box-sizing: border-box; padding: 0px 5px;">8</li><li style="box-sizing: border-box; padding: 0px 5px;">9</li><li style="box-sizing: border-box; padding: 0px 5px;">10</li><li style="box-sizing: border-box; padding: 0px 5px;">11</li><li style="box-sizing: border-box; padding: 0px 5px;">12</li><li style="box-sizing: border-box; padding: 0px 5px;">13</li><li style="box-sizing: border-box; padding: 0px 5px;">14</li><li style="box-sizing: border-box; padding: 0px 5px;">15</li><li style="box-sizing: border-box; padding: 0px 5px;">16</li><li style="box-sizing: border-box; padding: 0px 5px;">17</li><li style="box-sizing: border-box; padding: 0px 5px;">18</li><li style="box-sizing: border-box; padding: 0px 5px;">19</li><li style="box-sizing: border-box; padding: 0px 5px;">20</li><li style="box-sizing: border-box; padding: 0px 5px;">21</li><li style="box-sizing: border-box; padding: 0px 5px;">22</li><li style="box-sizing: border-box; padding: 0px 5px;">23</li></ul>
TLS是Thread Local Storage的缩写，表示线程本地存储，类似于Java中的ThreadLocal机制)pthread_getspecific和)pthread_setspecific方法分别提供了设置变量和获取变量的方法。
在这里我们看到了get方法，有get方法就一定有对应的set方法，set的设置就在构造函数中：
<code class="hljs avrasm has-numbering" style="display: block; padding: 0px; color: inherit; box-sizing: border-box; font-family: 'Source Code Pro', monospace;font-size:undefined; white-space: pre; border-radius: 0px; word-wrap: normal; background: transparent;"><span class="hljs-label" style="box-sizing: border-box;">IPCThreadState:</span>:IPCThreadState(): mProcess(ProcessState::self()),mMyThreadId(androidGetTid()),mStrictModePolicy(<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">0</span>),mLastTransactionBinderFlags(<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">0</span>)
{pthread_setspecific(gTLS, this)<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">;</span>clearCaller()<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">;</span>mIn<span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.setDataCapacity</span>(<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">256</span>)<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">;</span>mOut<span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.setDataCapacity</span>(<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">256</span>)<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">;</span>
}</code><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right; background-color: rgb(238, 238, 238);"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li><li style="box-sizing: border-box; padding: 0px 5px;">4</li><li style="box-sizing: border-box; padding: 0px 5px;">5</li><li style="box-sizing: border-box; padding: 0px 5px;">6</li><li style="box-sizing: border-box; padding: 0px 5px;">7</li><li style="box-sizing: border-box; padding: 0px 5px;">8</li><li style="box-sizing: border-box; padding: 0px 5px;">9</li><li style="box-sizing: border-box; padding: 0px 5px;">10</li><li style="box-sizing: border-box; padding: 0px 5px;">11</li></ul><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right; background-color: rgb(238, 238, 238);"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li><li style="box-sizing: border-box; padding: 0px 5px;">4</li><li style="box-sizing: border-box; padding: 0px 5px;">5</li><li style="box-sizing: border-box; padding: 0px 5px;">6</li><li style="box-sizing: border-box; padding: 0px 5px;">7</li><li style="box-sizing: border-box; padding: 0px 5px;">8</li><li style="box-sizing: border-box; padding: 0px 5px;">9</li><li style="box-sizing: border-box; padding: 0px 5px;">10</li><li style="box-sizing: border-box; padding: 0px 5px;">11</li></ul>
可以看到在构造函数中IPCThreadState将自身和线程本地存储关联起来了，在每一个IPCThreadState中都存在一个mIn和mOut，mIn用来存储接收Binder的数据，mOut用来存储发送到Binder的数据。
接下来看看transact方法：
<code class="hljs lasso has-numbering" style="display: block; padding: 0px; color: inherit; box-sizing: border-box; font-family: 'Source Code Pro', monospace;font-size:undefined; white-space: pre; border-radius: 0px; word-wrap: normal; background: transparent;">status_t IPCThreadState<span class="hljs-tag" style="color: rgb(0, 102, 102); box-sizing: border-box;">::transact</span>(int32_t <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">handle</span>,uint32_t code, const Parcel<span class="hljs-subst" style="color: rgb(0, 0, 0); box-sizing: border-box;">&</span> <span class="hljs-built_in" style="color: rgb(102, 0, 102); box-sizing: border-box;">data</span>,Parcel<span class="hljs-subst" style="color: rgb(0, 0, 0); box-sizing: border-box;">*</span> reply, uint32_t flags)
{status_t err <span class="hljs-subst" style="color: rgb(0, 0, 0); box-sizing: border-box;">=</span> <span class="hljs-built_in" style="color: rgb(102, 0, 102); box-sizing: border-box;">data</span><span class="hljs-built_in" style="color: rgb(102, 0, 102); box-sizing: border-box;">.</span>errorCheck();flags <span class="hljs-subst" style="color: rgb(0, 0, 0); box-sizing: border-box;">|=</span> TF_ACCEPT_FDS;<span class="hljs-attribute" style="box-sizing: border-box;">...</span><span class="hljs-attribute" style="box-sizing: border-box;">...</span><span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">if</span> (err <span class="hljs-subst" style="color: rgb(0, 0, 0); box-sizing: border-box;">==</span> NO_ERROR) {<span class="hljs-attribute" style="box-sizing: border-box;">...</span><span class="hljs-attribute" style="box-sizing: border-box;">...</span>err <span class="hljs-subst" style="color: rgb(0, 0, 0); box-sizing: border-box;">=</span> writeTransactionData(BC_TRANSACTION, flags, <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">handle</span>, code, <span class="hljs-built_in" style="color: rgb(102, 0, 102); box-sizing: border-box;">data</span>, <span class="hljs-built_in" style="color: rgb(102, 0, 102); box-sizing: border-box;">NULL</span>);} <span class="hljs-attribute" style="box-sizing: border-box;">...</span><span class="hljs-attribute" style="box-sizing: border-box;">...</span><span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">if</span> (reply) {err <span class="hljs-subst" style="color: rgb(0, 0, 0); box-sizing: border-box;">=</span> waitForResponse(reply);} <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">else</span> {Parcel fakeReply;err <span class="hljs-subst" style="color: rgb(0, 0, 0); box-sizing: border-box;">=</span> waitForResponse(<span class="hljs-subst" style="color: rgb(0, 0, 0); box-sizing: border-box;">&</span>fakeReply);}<span class="hljs-attribute" style="box-sizing: border-box;">...</span><span class="hljs-attribute" style="box-sizing: border-box;">...</span>} <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">else</span> {err <span class="hljs-subst" style="color: rgb(0, 0, 0); box-sizing: border-box;">=</span> waitForResponse(<span class="hljs-built_in" style="color: rgb(102, 0, 102); box-sizing: border-box;">NULL</span>, <span class="hljs-built_in" style="color: rgb(102, 0, 102); box-sizing: border-box;">NULL</span>);}<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">return</span> err;
}</code><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right; background-color: rgb(238, 238, 238);"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li><li style="box-sizing: border-box; padding: 0px 5px;">4</li><li style="box-sizing: border-box; padding: 0px 5px;">5</li><li style="box-sizing: border-box; padding: 0px 5px;">6</li><li style="box-sizing: border-box; padding: 0px 5px;">7</li><li style="box-sizing: border-box; padding: 0px 5px;">8</li><li style="box-sizing: border-box; padding: 0px 5px;">9</li><li style="box-sizing: border-box; padding: 0px 5px;">10</li><li style="box-sizing: border-box; padding: 0px 5px;">11</li><li style="box-sizing: border-box; padding: 0px 5px;">12</li><li style="box-sizing: border-box; padding: 0px 5px;">13</li><li style="box-sizing: border-box; padding: 0px 5px;">14</li><li style="box-sizing: border-box; padding: 0px 5px;">15</li><li style="box-sizing: border-box; padding: 0px 5px;">16</li><li style="box-sizing: border-box; padding: 0px 5px;">17</li><li style="box-sizing: border-box; padding: 0px 5px;">18</li><li style="box-sizing: border-box; padding: 0px 5px;">19</li><li style="box-sizing: border-box; padding: 0px 5px;">20</li><li style="box-sizing: border-box; padding: 0px 5px;">21</li><li style="box-sizing: border-box; padding: 0px 5px;">22</li><li style="box-sizing: border-box; padding: 0px 5px;">23</li><li style="box-sizing: border-box; padding: 0px 5px;">24</li><li style="box-sizing: border-box; padding: 0px 5px;">25</li><li style="box-sizing: border-box; padding: 0px 5px;">26</li></ul><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right; background-color: rgb(238, 238, 238);"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li><li style="box-sizing: border-box; padding: 0px 5px;">4</li><li style="box-sizing: border-box; padding: 0px 5px;">5</li><li style="box-sizing: border-box; padding: 0px 5px;">6</li><li style="box-sizing: border-box; padding: 0px 5px;">7</li><li style="box-sizing: border-box; padding: 0px 5px;">8</li><li style="box-sizing: border-box; padding: 0px 5px;">9</li><li style="box-sizing: border-box; padding: 0px 5px;">10</li><li style="box-sizing: border-box; padding: 0px 5px;">11</li><li style="box-sizing: border-box; padding: 0px 5px;">12</li><li style="box-sizing: border-box; padding: 0px 5px;">13</li><li style="box-sizing: border-box; padding: 0px 5px;">14</li><li style="box-sizing: border-box; padding: 0px 5px;">15</li><li style="box-sizing: border-box; padding: 0px 5px;">16</li><li style="box-sizing: border-box; padding: 0px 5px;">17</li><li style="box-sizing: border-box; padding: 0px 5px;">18</li><li style="box-sizing: border-box; padding: 0px 5px;">19</li><li style="box-sizing: border-box; padding: 0px 5px;">20</li><li style="box-sizing: border-box; padding: 0px 5px;">21</li><li style="box-sizing: border-box; padding: 0px 5px;">22</li><li style="box-sizing: border-box; padding: 0px 5px;">23</li><li style="box-sizing: border-box; padding: 0px 5px;">24</li><li style="box-sizing: border-box; padding: 0px 5px;">25</li><li style="box-sizing: border-box; padding: 0px 5px;">26</li></ul>
在这里省略了一些打印输出信息的语句，在这里我们可以清楚的看到通信的流程：先写入数据，然后等待接收数据。
如何进行通信
在前面我们知道了通信的流程，首先写入数据，之后等待回应，那么我们的通信就是这样不断的读写数据吗？接下来我们来一下看一下这两个读写的函数：
1.写入数据：
<code class="hljs avrasm has-numbering" style="display: block; padding: 0px; color: inherit; box-sizing: border-box; font-family: 'Source Code Pro', monospace;font-size:undefined; white-space: pre; border-radius: 0px; word-wrap: normal; background: transparent;">status_t IPCThreadState::writeTransactionData(int32_t cmd, uint32_t binderFlags,int32_t handle, uint32_t code, const Parcel& data, status_t* statusBuffer)
{binder_transaction_data tr<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">;</span>tr<span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.target</span><span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.handle</span> = handle<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">;</span>tr<span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.code</span> = code<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">;</span>tr<span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.flags</span> = binderFlags<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">;</span>tr<span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.cookie</span> = <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">0</span><span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">;</span>tr<span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.sender</span>_pid = <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">0</span><span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">;</span>tr<span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.sender</span>_euid = <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">0</span><span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">;</span>const status_t err = data<span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.errorCheck</span>()<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">;</span>if (err == NO_ERROR) {tr<span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.data</span>_size = data<span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.ipcDataSize</span>()<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">;</span>tr<span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.data</span><span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.ptr</span><span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.buffer</span> = data<span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.ipcData</span>()<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">;</span>tr<span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.offsets</span>_size = data<span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.ipcObjectsCount</span>()*sizeof(size_t)<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">;</span>tr<span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.data</span><span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.ptr</span><span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.offsets</span> = data<span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.ipcObjects</span>()<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">;</span>} else if (statusBuffer) {tr<span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.flags</span> |= TF_STATUS_CODE<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">;</span>*statusBuffer = err<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">;</span>tr<span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.data</span>_size = sizeof(status_t)<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">;</span>tr<span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.data</span><span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.ptr</span><span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.buffer</span> = statusBuffer<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">;</span>tr<span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.offsets</span>_size = <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">0</span><span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">;</span>tr<span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.data</span><span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.ptr</span><span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.offsets</span> = NULL<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">;</span>} else {return (mLastError = err)<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">;</span>}mOut<span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.writeInt</span>32(cmd)<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">;</span>mOut<span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.write</span>(&tr, sizeof(tr))<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">;</span>return NO_ERROR<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">;</span>
}</code><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right; background-color: rgb(238, 238, 238);"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li><li style="box-sizing: border-box; padding: 0px 5px;">4</li><li style="box-sizing: border-box; padding: 0px 5px;">5</li><li style="box-sizing: border-box; padding: 0px 5px;">6</li><li style="box-sizing: border-box; padding: 0px 5px;">7</li><li style="box-sizing: border-box; padding: 0px 5px;">8</li><li style="box-sizing: border-box; padding: 0px 5px;">9</li><li style="box-sizing: border-box; padding: 0px 5px;">10</li><li style="box-sizing: border-box; padding: 0px 5px;">11</li><li style="box-sizing: border-box; padding: 0px 5px;">12</li><li style="box-sizing: border-box; padding: 0px 5px;">13</li><li style="box-sizing: border-box; padding: 0px 5px;">14</li><li style="box-sizing: border-box; padding: 0px 5px;">15</li><li style="box-sizing: border-box; padding: 0px 5px;">16</li><li style="box-sizing: border-box; padding: 0px 5px;">17</li><li style="box-sizing: border-box; padding: 0px 5px;">18</li><li style="box-sizing: border-box; padding: 0px 5px;">19</li><li style="box-sizing: border-box; padding: 0px 5px;">20</li><li style="box-sizing: border-box; padding: 0px 5px;">21</li><li style="box-sizing: border-box; padding: 0px 5px;">22</li><li style="box-sizing: border-box; padding: 0px 5px;">23</li><li style="box-sizing: border-box; padding: 0px 5px;">24</li><li style="box-sizing: border-box; padding: 0px 5px;">25</li><li style="box-sizing: border-box; padding: 0px 5px;">26</li><li style="box-sizing: border-box; padding: 0px 5px;">27</li><li style="box-sizing: border-box; padding: 0px 5px;">28</li><li style="box-sizing: border-box; padding: 0px 5px;">29</li><li style="box-sizing: border-box; padding: 0px 5px;">30</li><li style="box-sizing: border-box; padding: 0px 5px;">31</li><li style="box-sizing: border-box; padding: 0px 5px;">32</li><li style="box-sizing: border-box; padding: 0px 5px;">33</li><li style="box-sizing: border-box; padding: 0px 5px;">34</li></ul><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right; background-color: rgb(238, 238, 238);"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li><li style="box-sizing: border-box; padding: 0px 5px;">4</li><li style="box-sizing: border-box; padding: 0px 5px;">5</li><li style="box-sizing: border-box; padding: 0px 5px;">6</li><li style="box-sizing: border-box; padding: 0px 5px;">7</li><li style="box-sizing: border-box; padding: 0px 5px;">8</li><li style="box-sizing: border-box; padding: 0px 5px;">9</li><li style="box-sizing: border-box; padding: 0px 5px;">10</li><li style="box-sizing: border-box; padding: 0px 5px;">11</li><li style="box-sizing: border-box; padding: 0px 5px;">12</li><li style="box-sizing: border-box; padding: 0px 5px;">13</li><li style="box-sizing: border-box; padding: 0px 5px;">14</li><li style="box-sizing: border-box; padding: 0px 5px;">15</li><li style="box-sizing: border-box; padding: 0px 5px;">16</li><li style="box-sizing: border-box; padding: 0px 5px;">17</li><li style="box-sizing: border-box; padding: 0px 5px;">18</li><li style="box-sizing: border-box; padding: 0px 5px;">19</li><li style="box-sizing: border-box; padding: 0px 5px;">20</li><li style="box-sizing: border-box; padding: 0px 5px;">21</li><li style="box-sizing: border-box; padding: 0px 5px;">22</li><li style="box-sizing: border-box; padding: 0px 5px;">23</li><li style="box-sizing: border-box; padding: 0px 5px;">24</li><li style="box-sizing: border-box; padding: 0px 5px;">25</li><li style="box-sizing: border-box; padding: 0px 5px;">26</li><li style="box-sizing: border-box; padding: 0px 5px;">27</li><li style="box-sizing: border-box; padding: 0px 5px;">28</li><li style="box-sizing: border-box; padding: 0px 5px;">29</li><li style="box-sizing: border-box; padding: 0px 5px;">30</li><li style="box-sizing: border-box; padding: 0px 5px;">31</li><li style="box-sizing: border-box; padding: 0px 5px;">32</li><li style="box-sizing: border-box; padding: 0px 5px;">33</li><li style="box-sizing: border-box; padding: 0px 5px;">34</li></ul>
在写入数据之前，我们首先对BpBinder进行了标识，在这里我们看到了之前所说的handle值，这样印证了之前一篇博客中所说的BBinder和BpBinder是由handle值来相互标识的。
2.等待回应：
<code class="hljs cpp has-numbering" style="display: block; padding: 0px; color: inherit; box-sizing: border-box; font-family: 'Source Code Pro', monospace;font-size:undefined; white-space: pre; border-radius: 0px; word-wrap: normal; background: transparent;">status_t IPCThreadState::waitForResponse(Parcel *reply, status_t *acquireResult)
{int32_t cmd;int32_t err;<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">while</span> (<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">1</span>) {<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">//talkWithDriver重要函数之一，负责从Binder中读写数据</span><span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">if</span> ((err=talkWithDriver()) < NO_ERROR) <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">break</span>;err = mIn.errorCheck();<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">if</span> (err < NO_ERROR) <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">break</span>;<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">if</span> (mIn.dataAvail() == <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">0</span>) <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">continue</span>;cmd = mIn.readInt32();<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">switch</span> (cmd) {<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">case</span> BR_TRANSACTION_COMPLETE:<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">//发送完一个数据包后，可以收到该消息做为成功发送的反馈。</span><span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">if</span> (!reply && !acquireResult) <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">goto</span> finish;<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">break</span>;<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">case</span> BR_DEAD_REPLY:<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">//交互过程中如果发现对方进程或线程已经死亡</span>err = DEAD_OBJECT;<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">goto</span> finish;<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">case</span> BR_FAILED_REPLY:<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">//发送失败</span>err = FAILED_TRANSACTION;<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">goto</span> finish;<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">case</span> BR_ACQUIRE_RESULT:<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">//获得结果</span>{<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">const</span> int32_t result = mIn.readInt32();<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">if</span> (!acquireResult) <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">continue</span>;*acquireResult = result ? NO_ERROR : INVALID_OPERATION;}<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">goto</span> finish;<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">case</span> BR_REPLY:<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">//当前接收的数据是回复</span>{binder_transaction_data tr;err = mIn.read(&tr, <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">sizeof</span>(tr));ALOG_ASSERT(err == NO_ERROR, <span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"Not enough command data for brREPLY"</span>);<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">if</span> (err != NO_ERROR) <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">goto</span> finish;<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">if</span> (reply) {<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">if</span> ((tr.flags & TF_STATUS_CODE) == <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">0</span>) {reply->ipcSetDataReference(<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">reinterpret_cast</span><<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">const</span> uint8_t*>(tr.data.ptr.buffer),tr.data_size,<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">reinterpret_cast</span><<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">const</span> size_t*>(tr.data.ptr.offsets),tr.offsets_size/<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">sizeof</span>(size_t),freeBuffer, <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">this</span>);} <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">else</span> {err = *<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">static_cast</span><<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">const</span> status_t*>(tr.data.ptr.buffer);freeBuffer(NULL,<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">reinterpret_cast</span><<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">const</span> uint8_t*>(tr.data.ptr.buffer),tr.data_size,<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">reinterpret_cast</span><<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">const</span> size_t*>(tr.data.ptr.offsets),tr.offsets_size/<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">sizeof</span>(size_t), <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">this</span>);}} <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">else</span> {freeBuffer(NULL,<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">reinterpret_cast</span><<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">const</span> uint8_t*>(tr.data.ptr.buffer),tr.data_size,<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">reinterpret_cast</span><<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">const</span> size_t*>(tr.data.ptr.offsets),tr.offsets_size/<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">sizeof</span>(size_t), <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">this</span>);<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">continue</span>;}}<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">goto</span> finish;<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">default</span>:<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">//第二个重要函数，处理命令</span>err = executeCommand(cmd);<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">if</span> (err != NO_ERROR) <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">goto</span> finish;<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">break</span>;}}finish:<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">if</span> (err != NO_ERROR) {<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">if</span> (acquireResult) *acquireResult = err;<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">if</span> (reply) reply->setError(err);mLastError = err;}<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">return</span> err;
}</code><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right; background-color: rgb(238, 238, 238);"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li><li style="box-sizing: border-box; padding: 0px 5px;">4</li><li style="box-sizing: border-box; padding: 0px 5px;">5</li><li style="box-sizing: border-box; padding: 0px 5px;">6</li><li style="box-sizing: border-box; padding: 0px 5px;">7</li><li style="box-sizing: border-box; padding: 0px 5px;">8</li><li style="box-sizing: border-box; padding: 0px 5px;">9</li><li style="box-sizing: border-box; padding: 0px 5px;">10</li><li style="box-sizing: border-box; padding: 0px 5px;">11</li><li style="box-sizing: border-box; padding: 0px 5px;">12</li><li style="box-sizing: border-box; padding: 0px 5px;">13</li><li style="box-sizing: border-box; padding: 0px 5px;">14</li><li style="box-sizing: border-box; padding: 0px 5px;">15</li><li style="box-sizing: border-box; padding: 0px 5px;">16</li><li style="box-sizing: border-box; padding: 0px 5px;">17</li><li style="box-sizing: border-box; padding: 0px 5px;">18</li><li style="box-sizing: border-box; padding: 0px 5px;">19</li><li style="box-sizing: border-box; padding: 0px 5px;">20</li><li style="box-sizing: border-box; padding: 0px 5px;">21</li><li style="box-sizing: border-box; padding: 0px 5px;">22</li><li style="box-sizing: border-box; padding: 0px 5px;">23</li><li style="box-sizing: border-box; padding: 0px 5px;">24</li><li style="box-sizing: border-box; padding: 0px 5px;">25</li><li style="box-sizing: border-box; padding: 0px 5px;">26</li><li style="box-sizing: border-box; padding: 0px 5px;">27</li><li style="box-sizing: border-box; padding: 0px 5px;">28</li><li style="box-sizing: border-box; padding: 0px 5px;">29</li><li style="box-sizing: border-box; padding: 0px 5px;">30</li><li style="box-sizing: border-box; padding: 0px 5px;">31</li><li style="box-sizing: border-box; padding: 0px 5px;">32</li><li style="box-sizing: border-box; padding: 0px 5px;">33</li><li style="box-sizing: border-box; padding: 0px 5px;">34</li><li style="box-sizing: border-box; padding: 0px 5px;">35</li><li style="box-sizing: border-box; padding: 0px 5px;">36</li><li style="box-sizing: border-box; padding: 0px 5px;">37</li><li style="box-sizing: border-box; padding: 0px 5px;">38</li><li style="box-sizing: border-box; padding: 0px 5px;">39</li><li style="box-sizing: border-box; padding: 0px 5px;">40</li><li style="box-sizing: border-box; padding: 0px 5px;">41</li><li style="box-sizing: border-box; padding: 0px 5px;">42</li><li style="box-sizing: border-box; padding: 0px 5px;">43</li><li style="box-sizing: border-box; padding: 0px 5px;">44</li><li style="box-sizing: border-box; padding: 0px 5px;">45</li><li style="box-sizing: border-box; padding: 0px 5px;">46</li><li style="box-sizing: border-box; padding: 0px 5px;">47</li><li style="box-sizing: border-box; padding: 0px 5px;">48</li><li style="box-sizing: border-box; padding: 0px 5px;">49</li><li style="box-sizing: border-box; padding: 0px 5px;">50</li><li style="box-sizing: border-box; padding: 0px 5px;">51</li><li style="box-sizing: border-box; padding: 0px 5px;">52</li><li style="box-sizing: border-box; padding: 0px 5px;">53</li><li style="box-sizing: border-box; padding: 0px 5px;">54</li><li style="box-sizing: border-box; padding: 0px 5px;">55</li><li style="box-sizing: border-box; padding: 0px 5px;">56</li><li style="box-sizing: border-box; padding: 0px 5px;">57</li><li style="box-sizing: border-box; padding: 0px 5px;">58</li><li style="box-sizing: border-box; padding: 0px 5px;">59</li><li style="box-sizing: border-box; padding: 0px 5px;">60</li><li style="box-sizing: border-box; padding: 0px 5px;">61</li><li style="box-sizing: border-box; padding: 0px 5px;">62</li><li style="box-sizing: border-box; padding: 0px 5px;">63</li><li style="box-sizing: border-box; padding: 0px 5px;">64</li><li style="box-sizing: border-box; padding: 0px 5px;">65</li><li style="box-sizing: border-box; padding: 0px 5px;">66</li><li style="box-sizing: border-box; padding: 0px 5px;">67</li><li style="box-sizing: border-box; padding: 0px 5px;">68</li><li style="box-sizing: border-box; padding: 0px 5px;">69</li><li style="box-sizing: border-box; padding: 0px 5px;">70</li><li style="box-sizing: border-box; padding: 0px 5px;">71</li><li style="box-sizing: border-box; padding: 0px 5px;">72</li><li style="box-sizing: border-box; padding: 0px 5px;">73</li><li style="box-sizing: border-box; padding: 0px 5px;">74</li><li style="box-sizing: border-box; padding: 0px 5px;">75</li><li style="box-sizing: border-box; padding: 0px 5px;">76</li><li style="box-sizing: border-box; padding: 0px 5px;">77</li><li style="box-sizing: border-box; padding: 0px 5px;">78</li><li style="box-sizing: border-box; padding: 0px 5px;">79</li><li style="box-sizing: border-box; padding: 0px 5px;">80</li><li style="box-sizing: border-box; padding: 0px 5px;">81</li><li style="box-sizing: border-box; padding: 0px 5px;">82</li><li style="box-sizing: border-box; padding: 0px 5px;">83</li><li style="box-sizing: border-box; padding: 0px 5px;">84</li><li style="box-sizing: border-box; padding: 0px 5px;">85</li><li style="box-sizing: border-box; padding: 0px 5px;">86</li></ul><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right; background-color: rgb(238, 238, 238);"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li><li style="box-sizing: border-box; padding: 0px 5px;">4</li><li style="box-sizing: border-box; padding: 0px 5px;">5</li><li style="box-sizing: border-box; padding: 0px 5px;">6</li><li style="box-sizing: border-box; padding: 0px 5px;">7</li><li style="box-sizing: border-box; padding: 0px 5px;">8</li><li style="box-sizing: border-box; padding: 0px 5px;">9</li><li style="box-sizing: border-box; padding: 0px 5px;">10</li><li style="box-sizing: border-box; padding: 0px 5px;">11</li><li style="box-sizing: border-box; padding: 0px 5px;">12</li><li style="box-sizing: border-box; padding: 0px 5px;">13</li><li style="box-sizing: border-box; padding: 0px 5px;">14</li><li style="box-sizing: border-box; padding: 0px 5px;">15</li><li style="box-sizing: border-box; padding: 0px 5px;">16</li><li style="box-sizing: border-box; padding: 0px 5px;">17</li><li style="box-sizing: border-box; padding: 0px 5px;">18</li><li style="box-sizing: border-box; padding: 0px 5px;">19</li><li style="box-sizing: border-box; padding: 0px 5px;">20</li><li style="box-sizing: border-box; padding: 0px 5px;">21</li><li style="box-sizing: border-box; padding: 0px 5px;">22</li><li style="box-sizing: border-box; padding: 0px 5px;">23</li><li style="box-sizing: border-box; padding: 0px 5px;">24</li><li style="box-sizing: border-box; padding: 0px 5px;">25</li><li style="box-sizing: border-box; padding: 0px 5px;">26</li><li style="box-sizing: border-box; padding: 0px 5px;">27</li><li style="box-sizing: border-box; padding: 0px 5px;">28</li><li style="box-sizing: border-box; padding: 0px 5px;">29</li><li style="box-sizing: border-box; padding: 0px 5px;">30</li><li style="box-sizing: border-box; padding: 0px 5px;">31</li><li style="box-sizing: border-box; padding: 0px 5px;">32</li><li style="box-sizing: border-box; padding: 0px 5px;">33</li><li style="box-sizing: border-box; padding: 0px 5px;">34</li><li style="box-sizing: border-box; padding: 0px 5px;">35</li><li style="box-sizing: border-box; padding: 0px 5px;">36</li><li style="box-sizing: border-box; padding: 0px 5px;">37</li><li style="box-sizing: border-box; padding: 0px 5px;">38</li><li style="box-sizing: border-box; padding: 0px 5px;">39</li><li style="box-sizing: border-box; padding: 0px 5px;">40</li><li style="box-sizing: border-box; padding: 0px 5px;">41</li><li style="box-sizing: border-box; padding: 0px 5px;">42</li><li style="box-sizing: border-box; padding: 0px 5px;">43</li><li style="box-sizing: border-box; padding: 0px 5px;">44</li><li style="box-sizing: border-box; padding: 0px 5px;">45</li><li style="box-sizing: border-box; padding: 0px 5px;">46</li><li style="box-sizing: border-box; padding: 0px 5px;">47</li><li style="box-sizing: border-box; padding: 0px 5px;">48</li><li style="box-sizing: border-box; padding: 0px 5px;">49</li><li style="box-sizing: border-box; padding: 0px 5px;">50</li><li style="box-sizing: border-box; padding: 0px 5px;">51</li><li style="box-sizing: border-box; padding: 0px 5px;">52</li><li style="box-sizing: border-box; padding: 0px 5px;">53</li><li style="box-sizing: border-box; padding: 0px 5px;">54</li><li style="box-sizing: border-box; padding: 0px 5px;">55</li><li style="box-sizing: border-box; padding: 0px 5px;">56</li><li style="box-sizing: border-box; padding: 0px 5px;">57</li><li style="box-sizing: border-box; padding: 0px 5px;">58</li><li style="box-sizing: border-box; padding: 0px 5px;">59</li><li style="box-sizing: border-box; padding: 0px 5px;">60</li><li style="box-sizing: border-box; padding: 0px 5px;">61</li><li style="box-sizing: border-box; padding: 0px 5px;">62</li><li style="box-sizing: border-box; padding: 0px 5px;">63</li><li style="box-sizing: border-box; padding: 0px 5px;">64</li><li style="box-sizing: border-box; padding: 0px 5px;">65</li><li style="box-sizing: border-box; padding: 0px 5px;">66</li><li style="box-sizing: border-box; padding: 0px 5px;">67</li><li style="box-sizing: border-box; padding: 0px 5px;">68</li><li style="box-sizing: border-box; padding: 0px 5px;">69</li><li style="box-sizing: border-box; padding: 0px 5px;">70</li><li style="box-sizing: border-box; padding: 0px 5px;">71</li><li style="box-sizing: border-box; padding: 0px 5px;">72</li><li style="box-sizing: border-box; padding: 0px 5px;">73</li><li style="box-sizing: border-box; padding: 0px 5px;">74</li><li style="box-sizing: border-box; padding: 0px 5px;">75</li><li style="box-sizing: border-box; padding: 0px 5px;">76</li><li style="box-sizing: border-box; padding: 0px 5px;">77</li><li style="box-sizing: border-box; padding: 0px 5px;">78</li><li style="box-sizing: border-box; padding: 0px 5px;">79</li><li style="box-sizing: border-box; padding: 0px 5px;">80</li><li style="box-sizing: border-box; padding: 0px 5px;">81</li><li style="box-sizing: border-box; padding: 0px 5px;">82</li><li style="box-sizing: border-box; padding: 0px 5px;">83</li><li style="box-sizing: border-box; padding: 0px 5px;">84</li><li style="box-sizing: border-box; padding: 0px 5px;">85</li><li style="box-sizing: border-box; padding: 0px 5px;">86</li></ul>
可以看到我们首先从Binder中读写数据，之后执行命令并返回结果状态码。
两个重要函数
IPCThreadState有两个重要的函数，talkWithDriver函数负责从Binder读写数据，executeCommand函数负责解析并执行mIn中的数据。
1.talkWithDriver：
<code class="hljs lasso has-numbering" style="display: block; padding: 0px; color: inherit; box-sizing: border-box; font-family: 'Source Code Pro', monospace;font-size:undefined; white-space: pre; border-radius: 0px; word-wrap: normal; background: transparent;">status_t IPCThreadState<span class="hljs-tag" style="color: rgb(0, 102, 102); box-sizing: border-box;">::talkWithDriver</span>(bool doReceive)
{
<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">//用来和Binder交换数据的结构</span>binder_write_read bwr;<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">// 判断数据是否为空</span>const bool needRead <span class="hljs-subst" style="color: rgb(0, 0, 0); box-sizing: border-box;">=</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">mIn</span><span class="hljs-built_in" style="color: rgb(102, 0, 102); box-sizing: border-box;">.</span>dataPosition() <span class="hljs-subst" style="color: rgb(0, 0, 0); box-sizing: border-box;">>=</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">mIn</span><span class="hljs-built_in" style="color: rgb(102, 0, 102); box-sizing: border-box;">.</span>dataSize();<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">// 如果caller已经请求读取下一行数据，或缓冲区中有数据没读完的时候我们不会进行任何写操作</span>const size_t outAvail <span class="hljs-subst" style="color: rgb(0, 0, 0); box-sizing: border-box;">=</span> (<span class="hljs-subst" style="color: rgb(0, 0, 0); box-sizing: border-box;">!</span>doReceive <span class="hljs-subst" style="color: rgb(0, 0, 0); box-sizing: border-box;">||</span> needRead) <span class="hljs-subst" style="color: rgb(0, 0, 0); box-sizing: border-box;">?</span> mOut<span class="hljs-built_in" style="color: rgb(102, 0, 102); box-sizing: border-box;">.</span>dataSize() : <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">0</span>;<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">//填充请求命令</span>bwr<span class="hljs-built_in" style="color: rgb(102, 0, 102); box-sizing: border-box;">.</span>write_size <span class="hljs-subst" style="color: rgb(0, 0, 0); box-sizing: border-box;">=</span> outAvail;bwr<span class="hljs-built_in" style="color: rgb(102, 0, 102); box-sizing: border-box;">.</span>write_buffer <span class="hljs-subst" style="color: rgb(0, 0, 0); box-sizing: border-box;">=</span> (long unsigned int)mOut<span class="hljs-built_in" style="color: rgb(102, 0, 102); box-sizing: border-box;">.</span><span class="hljs-built_in" style="color: rgb(102, 0, 102); box-sizing: border-box;">data</span>();<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">if</span> (doReceive <span class="hljs-subst" style="color: rgb(0, 0, 0); box-sizing: border-box;">&&</span> needRead) {bwr<span class="hljs-built_in" style="color: rgb(102, 0, 102); box-sizing: border-box;">.</span>read_size <span class="hljs-subst" style="color: rgb(0, 0, 0); box-sizing: border-box;">=</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">mIn</span><span class="hljs-built_in" style="color: rgb(102, 0, 102); box-sizing: border-box;">.</span>dataCapacity();bwr<span class="hljs-built_in" style="color: rgb(102, 0, 102); box-sizing: border-box;">.</span>read_buffer <span class="hljs-subst" style="color: rgb(0, 0, 0); box-sizing: border-box;">=</span> (long unsigned int)<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">mIn</span><span class="hljs-built_in" style="color: rgb(102, 0, 102); box-sizing: border-box;">.</span><span class="hljs-built_in" style="color: rgb(102, 0, 102); box-sizing: border-box;">data</span>();<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">//mIn用来存储接收的Binder数据</span>} <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">else</span> {bwr<span class="hljs-built_in" style="color: rgb(102, 0, 102); box-sizing: border-box;">.</span>read_size <span class="hljs-subst" style="color: rgb(0, 0, 0); box-sizing: border-box;">=</span> <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">0</span>;bwr<span class="hljs-built_in" style="color: rgb(102, 0, 102); box-sizing: border-box;">.</span>read_buffer <span class="hljs-subst" style="color: rgb(0, 0, 0); box-sizing: border-box;">=</span> <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">0</span>;}
<span class="hljs-attribute" style="box-sizing: border-box;">...</span><span class="hljs-attribute" style="box-sizing: border-box;">...</span><span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">// 如果不需要任何操作了立即返回.</span><span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">if</span> ((bwr<span class="hljs-built_in" style="color: rgb(102, 0, 102); box-sizing: border-box;">.</span>write_size <span class="hljs-subst" style="color: rgb(0, 0, 0); box-sizing: border-box;">==</span> <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">0</span>) <span class="hljs-subst" style="color: rgb(0, 0, 0); box-sizing: border-box;">&&</span> (bwr<span class="hljs-built_in" style="color: rgb(102, 0, 102); box-sizing: border-box;">.</span>read_size <span class="hljs-subst" style="color: rgb(0, 0, 0); box-sizing: border-box;">==</span> <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">0</span>)) <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">return</span> NO_ERROR;bwr<span class="hljs-built_in" style="color: rgb(102, 0, 102); box-sizing: border-box;">.</span>write_consumed <span class="hljs-subst" style="color: rgb(0, 0, 0); box-sizing: border-box;">=</span> <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">0</span>;bwr<span class="hljs-built_in" style="color: rgb(102, 0, 102); box-sizing: border-box;">.</span>read_consumed <span class="hljs-subst" style="color: rgb(0, 0, 0); box-sizing: border-box;">=</span> <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">0</span>;status_t err;<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">do</span> {
<span class="hljs-variable" style="color: rgb(102, 0, 102); box-sizing: border-box;">#if</span> defined(HAVE_ANDROID_OS)
<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">//ioctl方式进行通信</span><span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">if</span> (ioctl(mProcess<span class="hljs-subst" style="color: rgb(0, 0, 0); box-sizing: border-box;">-></span>mDriverFD, BINDER_WRITE_READ, <span class="hljs-subst" style="color: rgb(0, 0, 0); box-sizing: border-box;">&</span>bwr) <span class="hljs-subst" style="color: rgb(0, 0, 0); box-sizing: border-box;">>=</span> <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">0</span>)err <span class="hljs-subst" style="color: rgb(0, 0, 0); box-sizing: border-box;">=</span> NO_ERROR;<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">else</span>err <span class="hljs-subst" style="color: rgb(0, 0, 0); box-sizing: border-box;">=</span> <span class="hljs-attribute" style="box-sizing: border-box;">-errno</span>;
<span class="hljs-variable" style="color: rgb(102, 0, 102); box-sizing: border-box;">#else</span>err <span class="hljs-subst" style="color: rgb(0, 0, 0); box-sizing: border-box;">=</span> INVALID_OPERATION;
<span class="hljs-variable" style="color: rgb(102, 0, 102); box-sizing: border-box;">#endif</span>} <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">while</span> (err <span class="hljs-subst" style="color: rgb(0, 0, 0); box-sizing: border-box;">==</span> <span class="hljs-attribute" style="box-sizing: border-box;">-EINTR</span>);<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">if</span> (err <span class="hljs-subst" style="color: rgb(0, 0, 0); box-sizing: border-box;">>=</span> NO_ERROR) {<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">if</span> (bwr<span class="hljs-built_in" style="color: rgb(102, 0, 102); box-sizing: border-box;">.</span>write_consumed <span class="hljs-subst" style="color: rgb(0, 0, 0); box-sizing: border-box;">></span> <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">0</span>) {<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">if</span> (bwr<span class="hljs-built_in" style="color: rgb(102, 0, 102); box-sizing: border-box;">.</span>write_consumed <span class="hljs-subst" style="color: rgb(0, 0, 0); box-sizing: border-box;"><</span> (ssize_t)mOut<span class="hljs-built_in" style="color: rgb(102, 0, 102); box-sizing: border-box;">.</span>dataSize())mOut<span class="hljs-built_in" style="color: rgb(102, 0, 102); box-sizing: border-box;">.</span>remove(<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">0</span>, bwr<span class="hljs-built_in" style="color: rgb(102, 0, 102); box-sizing: border-box;">.</span>write_consumed);<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">else</span>mOut<span class="hljs-built_in" style="color: rgb(102, 0, 102); box-sizing: border-box;">.</span>setDataSize(<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">0</span>);}<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">if</span> (bwr<span class="hljs-built_in" style="color: rgb(102, 0, 102); box-sizing: border-box;">.</span>read_consumed <span class="hljs-subst" style="color: rgb(0, 0, 0); box-sizing: border-box;">></span> <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">0</span>) {<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">mIn</span><span class="hljs-built_in" style="color: rgb(102, 0, 102); box-sizing: border-box;">.</span>setDataSize(bwr<span class="hljs-built_in" style="color: rgb(102, 0, 102); box-sizing: border-box;">.</span>read_consumed);<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">mIn</span><span class="hljs-built_in" style="color: rgb(102, 0, 102); box-sizing: border-box;">.</span>setDataPosition(<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">0</span>);}<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">return</span> NO_ERROR;} <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">return</span> err;
}</code><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right; background-color: rgb(238, 238, 238);"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li><li style="box-sizing: border-box; padding: 0px 5px;">4</li><li style="box-sizing: border-box; padding: 0px 5px;">5</li><li style="box-sizing: border-box; padding: 0px 5px;">6</li><li style="box-sizing: border-box; padding: 0px 5px;">7</li><li style="box-sizing: border-box; padding: 0px 5px;">8</li><li style="box-sizing: border-box; padding: 0px 5px;">9</li><li style="box-sizing: border-box; padding: 0px 5px;">10</li><li style="box-sizing: border-box; padding: 0px 5px;">11</li><li style="box-sizing: border-box; padding: 0px 5px;">12</li><li style="box-sizing: border-box; padding: 0px 5px;">13</li><li style="box-sizing: border-box; padding: 0px 5px;">14</li><li style="box-sizing: border-box; padding: 0px 5px;">15</li><li style="box-sizing: border-box; padding: 0px 5px;">16</li><li style="box-sizing: border-box; padding: 0px 5px;">17</li><li style="box-sizing: border-box; padding: 0px 5px;">18</li><li style="box-sizing: border-box; padding: 0px 5px;">19</li><li style="box-sizing: border-box; padding: 0px 5px;">20</li><li style="box-sizing: border-box; padding: 0px 5px;">21</li><li style="box-sizing: border-box; padding: 0px 5px;">22</li><li style="box-sizing: border-box; padding: 0px 5px;">23</li><li style="box-sizing: border-box; padding: 0px 5px;">24</li><li style="box-sizing: border-box; padding: 0px 5px;">25</li><li style="box-sizing: border-box; padding: 0px 5px;">26</li><li style="box-sizing: border-box; padding: 0px 5px;">27</li><li style="box-sizing: border-box; padding: 0px 5px;">28</li><li style="box-sizing: border-box; padding: 0px 5px;">29</li><li style="box-sizing: border-box; padding: 0px 5px;">30</li><li style="box-sizing: border-box; padding: 0px 5px;">31</li><li style="box-sizing: border-box; padding: 0px 5px;">32</li><li style="box-sizing: border-box; padding: 0px 5px;">33</li><li style="box-sizing: border-box; padding: 0px 5px;">34</li><li style="box-sizing: border-box; padding: 0px 5px;">35</li><li style="box-sizing: border-box; padding: 0px 5px;">36</li><li style="box-sizing: border-box; padding: 0px 5px;">37</li><li style="box-sizing: border-box; padding: 0px 5px;">38</li><li style="box-sizing: border-box; padding: 0px 5px;">39</li><li style="box-sizing: border-box; padding: 0px 5px;">40</li><li style="box-sizing: border-box; padding: 0px 5px;">41</li><li style="box-sizing: border-box; padding: 0px 5px;">42</li><li style="box-sizing: border-box; padding: 0px 5px;">43</li><li style="box-sizing: border-box; padding: 0px 5px;">44</li><li style="box-sizing: border-box; padding: 0px 5px;">45</li><li style="box-sizing: border-box; padding: 0px 5px;">46</li><li style="box-sizing: border-box; padding: 0px 5px;">47</li><li style="box-sizing: border-box; padding: 0px 5px;">48</li><li style="box-sizing: border-box; padding: 0px 5px;">49</li><li style="box-sizing: border-box; padding: 0px 5px;">50</li><li style="box-sizing: border-box; padding: 0px 5px;">51</li><li style="box-sizing: border-box; padding: 0px 5px;">52</li><li style="box-sizing: border-box; padding: 0px 5px;">53</li><li style="box-sizing: border-box; padding: 0px 5px;">54</li><li style="box-sizing: border-box; padding: 0px 5px;">55</li></ul><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right; background-color: rgb(238, 238, 238);"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li><li style="box-sizing: border-box; padding: 0px 5px;">4</li><li style="box-sizing: border-box; padding: 0px 5px;">5</li><li style="box-sizing: border-box; padding: 0px 5px;">6</li><li style="box-sizing: border-box; padding: 0px 5px;">7</li><li style="box-sizing: border-box; padding: 0px 5px;">8</li><li style="box-sizing: border-box; padding: 0px 5px;">9</li><li style="box-sizing: border-box; padding: 0px 5px;">10</li><li style="box-sizing: border-box; padding: 0px 5px;">11</li><li style="box-sizing: border-box; padding: 0px 5px;">12</li><li style="box-sizing: border-box; padding: 0px 5px;">13</li><li style="box-sizing: border-box; padding: 0px 5px;">14</li><li style="box-sizing: border-box; padding: 0px 5px;">15</li><li style="box-sizing: border-box; padding: 0px 5px;">16</li><li style="box-sizing: border-box; padding: 0px 5px;">17</li><li style="box-sizing: border-box; padding: 0px 5px;">18</li><li style="box-sizing: border-box; padding: 0px 5px;">19</li><li style="box-sizing: border-box; padding: 0px 5px;">20</li><li style="box-sizing: border-box; padding: 0px 5px;">21</li><li style="box-sizing: border-box; padding: 0px 5px;">22</li><li style="box-sizing: border-box; padding: 0px 5px;">23</li><li style="box-sizing: border-box; padding: 0px 5px;">24</li><li style="box-sizing: border-box; padding: 0px 5px;">25</li><li style="box-sizing: border-box; padding: 0px 5px;">26</li><li style="box-sizing: border-box; padding: 0px 5px;">27</li><li style="box-sizing: border-box; padding: 0px 5px;">28</li><li style="box-sizing: border-box; padding: 0px 5px;">29</li><li style="box-sizing: border-box; padding: 0px 5px;">30</li><li style="box-sizing: border-box; padding: 0px 5px;">31</li><li style="box-sizing: border-box; padding: 0px 5px;">32</li><li style="box-sizing: border-box; padding: 0px 5px;">33</li><li style="box-sizing: border-box; padding: 0px 5px;">34</li><li style="box-sizing: border-box; padding: 0px 5px;">35</li><li style="box-sizing: border-box; padding: 0px 5px;">36</li><li style="box-sizing: border-box; padding: 0px 5px;">37</li><li style="box-sizing: border-box; padding: 0px 5px;">38</li><li style="box-sizing: border-box; padding: 0px 5px;">39</li><li style="box-sizing: border-box; padding: 0px 5px;">40</li><li style="box-sizing: border-box; padding: 0px 5px;">41</li><li style="box-sizing: border-box; padding: 0px 5px;">42</li><li style="box-sizing: border-box; padding: 0px 5px;">43</li><li style="box-sizing: border-box; padding: 0px 5px;">44</li><li style="box-sizing: border-box; padding: 0px 5px;">45</li><li style="box-sizing: border-box; padding: 0px 5px;">46</li><li style="box-sizing: border-box; padding: 0px 5px;">47</li><li style="box-sizing: border-box; padding: 0px 5px;">48</li><li style="box-sizing: border-box; padding: 0px 5px;">49</li><li style="box-sizing: border-box; padding: 0px 5px;">50</li><li style="box-sizing: border-box; padding: 0px 5px;">51</li><li style="box-sizing: border-box; padding: 0px 5px;">52</li><li style="box-sizing: border-box; padding: 0px 5px;">53</li><li style="box-sizing: border-box; padding: 0px 5px;">54</li><li style="box-sizing: border-box; padding: 0px 5px;">55</li></ul>
可以看到我们的Binder通信并不是采用的读写方式，而是ioctl方式，什么是ioctl方式呢？
ioctl是设备驱动程序中对设备的I/O通道进行管理的函数。所谓对I/O通道进行管理，就是对设备的一些特性进行控制，例如串口的传输波特率、马达的 转速等等。它的调用函数如下：int ioctl(int fd, ind cmd, …)；其中fd就是用户程序打开设备时使用open函数返回的文件标示符，cmd就是用户程序对设备的控制命令。
2.executeCommand函数：
<code class="hljs cpp has-numbering" style="display: block; padding: 0px; color: inherit; box-sizing: border-box; font-family: 'Source Code Pro', monospace;font-size:undefined; white-space: pre; border-radius: 0px; word-wrap: normal; background: transparent;">status_t IPCThreadState::executeCommand(int32_t cmd)
{BBinder* obj;RefBase::weakref_type* refs;status_t result = NO_ERROR;<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">switch</span> (cmd) {<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">case</span> BR_ERROR:result = mIn.readInt32();<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">break</span>;<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">case</span> BR_OK:<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">break</span>;<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">case</span> BR_ACQUIRE:refs = (RefBase::weakref_type*)mIn.readInt32();obj = (BBinder*)mIn.readInt32();obj->incStrong(mProcess.get()); mOut.writeInt32(BC_ACQUIRE_DONE);mOut.writeInt32((int32_t)refs);mOut.writeInt32((int32_t)obj);<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">break</span>;<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">case</span> BR_RELEASE:refs = (RefBase::weakref_type*)mIn.readInt32();obj = (BBinder*)mIn.readInt32();mPendingStrongDerefs.push(obj);<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">break</span>;<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">case</span> BR_INCREFS:refs = (RefBase::weakref_type*)mIn.readInt32();obj = (BBinder*)mIn.readInt32();refs->incWeak(mProcess.get());mOut.writeInt32(BC_INCREFS_DONE);mOut.writeInt32((int32_t)refs);mOut.writeInt32((int32_t)obj);<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">break</span>;<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">case</span> BR_DECREFS:refs = (RefBase::weakref_type*)mIn.readInt32();obj = (BBinder*)mIn.readInt32();mPendingWeakDerefs.push(refs);<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">break</span>;<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">case</span> BR_ATTEMPT_ACQUIRE:refs = (RefBase::weakref_type*)mIn.readInt32();obj = (BBinder*)mIn.readInt32();{<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">const</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">bool</span> success = refs->attemptIncStrong(mProcess.get());mOut.writeInt32(BC_ACQUIRE_RESULT);mOut.writeInt32((int32_t)success);}<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">break</span>;<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">case</span> BR_TRANSACTION:<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">//当前接收的数据是请求</span>{binder_transaction_data tr;result = mIn.read(&tr, <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">sizeof</span>(tr));<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">if</span> (result != NO_ERROR) <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">break</span>;Parcel buffer;buffer.ipcSetDataReference(<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">reinterpret_cast</span><<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">const</span> uint8_t*>(tr.data.ptr.buffer),tr.data_size,<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">reinterpret_cast</span><<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">const</span> size_t*>(tr.data.ptr.offsets),tr.offsets_size/<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">sizeof</span>(size_t), freeBuffer, <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">this</span>);<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">const</span> pid_t origPid = mCallingPid;<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">const</span> uid_t origUid = mCallingUid;mCallingPid = tr.sender_pid;mCallingUid = tr.sender_euid;<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">int</span> curPrio = getpriority(PRIO_PROCESS, mMyThreadId);<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">if</span> (gDisableBackgroundScheduling) {<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">if</span> (curPrio > ANDROID_PRIORITY_NORMAL) {<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">//我们已经从caller实现了一个减小的优先级，但我们不希望它以这</span><span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">//种状态运行在进程中。驱动已经设置了优先级，所以在开始事务</span><span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">//前首先将他设置为默认 </span>setpriority(PRIO_PROCESS, mMyThreadId, ANDROID_PRIORITY_NORMAL);}} <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">else</span> {<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">if</span> (curPrio >= ANDROID_PRIORITY_BACKGROUND) {androidSetThreadSchedulingGroup(mMyThreadId, ANDROID_TGROUP_BG_NONINTERACT);}}Parcel reply;<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">if</span> (tr.target.ptr) {<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">//在这里我们看到了BBinder，还记得吗，BBinder和BpBinder相对应，</span><span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">//是交互的目的端</span>sp<BBinder> b((BBinder*)tr.cookie);<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">//在transact函数中调用了onTransact方法向reply写入数据</span><span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">const</span> status_t error = b->transact(tr.code, buffer, &reply, tr.flags);<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">if</span> (error < NO_ERROR) reply.setError(error);} <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">else</span> {<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">const</span> status_t error = the_context_object->transact(tr.code, buffer, &reply, tr.flags);<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">if</span> (error < NO_ERROR) reply.setError(error);}<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">if</span> ((tr.flags & TF_ONE_WAY) == <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">0</span>) {sendReply(reply, <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">0</span>);} mCallingPid = origPid;mCallingUid = origUid; }<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">break</span>;<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">case</span> BR_DEAD_BINDER:{BpBinder *proxy = (BpBinder*)mIn.readInt32();proxy->sendObituary();mOut.writeInt32(BC_DEAD_BINDER_DONE);mOut.writeInt32((int32_t)proxy);} <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">break</span>;<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">case</span> BR_CLEAR_DEATH_NOTIFICATION_DONE:{BpBinder *proxy = (BpBinder*)mIn.readInt32();proxy->getWeakRefs()->decWeak(proxy);} <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">break</span>;<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">case</span> BR_FINISHED:result = TIMED_OUT;<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">break</span>;<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">case</span> BR_NOOP:<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">break</span>;<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">case</span> BR_SPAWN_LOOPER:<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">//用于接收方线程池管理。当驱动发现接收方所有线程都处于忙碌状态且线</span><span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">//程池里的线程总数没有超过BINDER_SET_MAX_THREADS设置的最大线程数 </span><span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">//时，向接收方发送该命令要求创建更多线程以备接收数据。</span>mProcess->spawnPooledThread(<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">false</span>);<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">break</span>;<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">default</span>:<span class="hljs-built_in" style="color: rgb(102, 0, 102); box-sizing: border-box;">printf</span>(<span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"*** BAD COMMAND %d received from Binder driver\n"</span>, cmd);result = UNKNOWN_ERROR;<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">break</span>;}<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">if</span> (result != NO_ERROR) {mLastError = result;}<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">return</span> result;
}</code><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right; background-color: rgb(238, 238, 238);"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li><li style="box-sizing: border-box; padding: 0px 5px;">4</li><li style="box-sizing: border-box; padding: 0px 5px;">5</li><li style="box-sizing: border-box; padding: 0px 5px;">6</li><li style="box-sizing: border-box; padding: 0px 5px;">7</li><li style="box-sizing: border-box; padding: 0px 5px;">8</li><li style="box-sizing: border-box; padding: 0px 5px;">9</li><li style="box-sizing: border-box; padding: 0px 5px;">10</li><li style="box-sizing: border-box; padding: 0px 5px;">11</li><li style="box-sizing: border-box; padding: 0px 5px;">12</li><li style="box-sizing: border-box; padding: 0px 5px;">13</li><li style="box-sizing: border-box; padding: 0px 5px;">14</li><li style="box-sizing: border-box; padding: 0px 5px;">15</li><li style="box-sizing: border-box; padding: 0px 5px;">16</li><li style="box-sizing: border-box; padding: 0px 5px;">17</li><li style="box-sizing: border-box; padding: 0px 5px;">18</li><li style="box-sizing: border-box; padding: 0px 5px;">19</li><li style="box-sizing: border-box; padding: 0px 5px;">20</li><li style="box-sizing: border-box; padding: 0px 5px;">21</li><li style="box-sizing: border-box; padding: 0px 5px;">22</li><li style="box-sizing: border-box; padding: 0px 5px;">23</li><li style="box-sizing: border-box; padding: 0px 5px;">24</li><li style="box-sizing: border-box; padding: 0px 5px;">25</li><li style="box-sizing: border-box; padding: 0px 5px;">26</li><li style="box-sizing: border-box; padding: 0px 5px;">27</li><li style="box-sizing: border-box; padding: 0px 5px;">28</li><li style="box-sizing: border-box; padding: 0px 5px;">29</li><li style="box-sizing: border-box; padding: 0px 5px;">30</li><li style="box-sizing: border-box; padding: 0px 5px;">31</li><li style="box-sizing: border-box; padding: 0px 5px;">32</li><li style="box-sizing: border-box; padding: 0px 5px;">33</li><li style="box-sizing: border-box; padding: 0px 5px;">34</li><li style="box-sizing: border-box; padding: 0px 5px;">35</li><li style="box-sizing: border-box; padding: 0px 5px;">36</li><li style="box-sizing: border-box; padding: 0px 5px;">37</li><li style="box-sizing: border-box; padding: 0px 5px;">38</li><li style="box-sizing: border-box; padding: 0px 5px;">39</li><li style="box-sizing: border-box; padding: 0px 5px;">40</li><li style="box-sizing: border-box; padding: 0px 5px;">41</li><li style="box-sizing: border-box; padding: 0px 5px;">42</li><li style="box-sizing: border-box; padding: 0px 5px;">43</li><li style="box-sizing: border-box; padding: 0px 5px;">44</li><li style="box-sizing: border-box; padding: 0px 5px;">45</li><li style="box-sizing: border-box; padding: 0px 5px;">46</li><li style="box-sizing: border-box; padding: 0px 5px;">47</li><li style="box-sizing: border-box; padding: 0px 5px;">48</li><li style="box-sizing: border-box; padding: 0px 5px;">49</li><li style="box-sizing: border-box; padding: 0px 5px;">50</li><li style="box-sizing: border-box; padding: 0px 5px;">51</li><li style="box-sizing: border-box; padding: 0px 5px;">52</li><li style="box-sizing: border-box; padding: 0px 5px;">53</li><li style="box-sizing: border-box; padding: 0px 5px;">54</li><li style="box-sizing: border-box; padding: 0px 5px;">55</li><li style="box-sizing: border-box; padding: 0px 5px;">56</li><li style="box-sizing: border-box; padding: 0px 5px;">57</li><li style="box-sizing: border-box; padding: 0px 5px;">58</li><li style="box-sizing: border-box; padding: 0px 5px;">59</li><li style="box-sizing: border-box; padding: 0px 5px;">60</li><li style="box-sizing: border-box; padding: 0px 5px;">61</li><li style="box-sizing: border-box; padding: 0px 5px;">62</li><li style="box-sizing: border-box; padding: 0px 5px;">63</li><li style="box-sizing: border-box; padding: 0px 5px;">64</li><li style="box-sizing: border-box; padding: 0px 5px;">65</li><li style="box-sizing: border-box; padding: 0px 5px;">66</li><li style="box-sizing: border-box; padding: 0px 5px;">67</li><li style="box-sizing: border-box; padding: 0px 5px;">68</li><li style="box-sizing: border-box; padding: 0px 5px;">69</li><li style="box-sizing: border-box; padding: 0px 5px;">70</li><li style="box-sizing: border-box; padding: 0px 5px;">71</li><li style="box-sizing: border-box; padding: 0px 5px;">72</li><li style="box-sizing: border-box; padding: 0px 5px;">73</li><li style="box-sizing: border-box; padding: 0px 5px;">74</li><li style="box-sizing: border-box; padding: 0px 5px;">75</li><li style="box-sizing: border-box; padding: 0px 5px;">76</li><li style="box-sizing: border-box; padding: 0px 5px;">77</li><li style="box-sizing: border-box; padding: 0px 5px;">78</li><li style="box-sizing: border-box; padding: 0px 5px;">79</li><li style="box-sizing: border-box; padding: 0px 5px;">80</li><li style="box-sizing: border-box; padding: 0px 5px;">81</li><li style="box-sizing: border-box; padding: 0px 5px;">82</li><li style="box-sizing: border-box; padding: 0px 5px;">83</li><li style="box-sizing: border-box; padding: 0px 5px;">84</li><li style="box-sizing: border-box; padding: 0px 5px;">85</li><li style="box-sizing: border-box; padding: 0px 5px;">86</li><li style="box-sizing: border-box; padding: 0px 5px;">87</li><li style="box-sizing: border-box; padding: 0px 5px;">88</li><li style="box-sizing: border-box; padding: 0px 5px;">89</li><li style="box-sizing: border-box; padding: 0px 5px;">90</li><li style="box-sizing: border-box; padding: 0px 5px;">91</li><li style="box-sizing: border-box; padding: 0px 5px;">92</li><li style="box-sizing: border-box; padding: 0px 5px;">93</li><li style="box-sizing: border-box; padding: 0px 5px;">94</li><li style="box-sizing: border-box; padding: 0px 5px;">95</li><li style="box-sizing: border-box; padding: 0px 5px;">96</li><li style="box-sizing: border-box; padding: 0px 5px;">97</li><li style="box-sizing: border-box; padding: 0px 5px;">98</li><li style="box-sizing: border-box; padding: 0px 5px;">99</li><li style="box-sizing: border-box; padding: 0px 5px;">100</li><li style="box-sizing: border-box; padding: 0px 5px;">101</li><li style="box-sizing: border-box; padding: 0px 5px;">102</li><li style="box-sizing: border-box; padding: 0px 5px;">103</li><li style="box-sizing: border-box; padding: 0px 5px;">104</li><li style="box-sizing: border-box; padding: 0px 5px;">105</li><li style="box-sizing: border-box; padding: 0px 5px;">106</li><li style="box-sizing: border-box; padding: 0px 5px;">107</li><li style="box-sizing: border-box; padding: 0px 5px;">108</li><li style="box-sizing: border-box; padding: 0px 5px;">109</li><li style="box-sizing: border-box; padding: 0px 5px;">110</li><li style="box-sizing: border-box; padding: 0px 5px;">111</li><li style="box-sizing: border-box; padding: 0px 5px;">112</li><li style="box-sizing: border-box; padding: 0px 5px;">113</li><li style="box-sizing: border-box; padding: 0px 5px;">114</li><li style="box-sizing: border-box; padding: 0px 5px;">115</li><li style="box-sizing: border-box; padding: 0px 5px;">116</li><li style="box-sizing: border-box; padding: 0px 5px;">117</li><li style="box-sizing: border-box; padding: 0px 5px;">118</li><li style="box-sizing: border-box; padding: 0px 5px;">119</li><li style="box-sizing: border-box; padding: 0px 5px;">120</li><li style="box-sizing: border-box; padding: 0px 5px;">121</li><li style="box-sizing: border-box; padding: 0px 5px;">122</li><li style="box-sizing: border-box; padding: 0px 5px;">123</li><li style="box-sizing: border-box; padding: 0px 5px;">124</li><li style="box-sizing: border-box; padding: 0px 5px;">125</li><li style="box-sizing: border-box; padding: 0px 5px;">126</li><li style="box-sizing: border-box; padding: 0px 5px;">127</li><li style="box-sizing: border-box; padding: 0px 5px;">128</li><li style="box-sizing: border-box; padding: 0px 5px;">129</li><li style="box-sizing: border-box; padding: 0px 5px;">130</li><li style="box-sizing: border-box; padding: 0px 5px;">131</li><li style="box-sizing: border-box; padding: 0px 5px;">132</li><li style="box-sizing: border-box; padding: 0px 5px;">133</li><li style="box-sizing: border-box; padding: 0px 5px;">134</li><li style="box-sizing: border-box; padding: 0px 5px;">135</li><li style="box-sizing: border-box; padding: 0px 5px;">136</li><li style="box-sizing: border-box; padding: 0px 5px;">137</li><li style="box-sizing: border-box; padding: 0px 5px;">138</li><li style="box-sizing: border-box; padding: 0px 5px;">139</li><li style="box-sizing: border-box; padding: 0px 5px;">140</li><li style="box-sizing: border-box; padding: 0px 5px;">141</li><li style="box-sizing: border-box; padding: 0px 5px;">142</li><li style="box-sizing: border-box; padding: 0px 5px;">143</li><li style="box-sizing: border-box; padding: 0px 5px;">144</li><li style="box-sizing: border-box; padding: 0px 5px;">145</li><li style="box-sizing: border-box; padding: 0px 5px;">146</li><li style="box-sizing: border-box; padding: 0px 5px;">147</li><li style="box-sizing: border-box; padding: 0px 5px;">148</li><li style="box-sizing: border-box; padding: 0px 5px;">149</li><li style="box-sizing: border-box; padding: 0px 5px;">150</li></ul><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right; background-color: rgb(238, 238, 238);"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li><li style="box-sizing: border-box; padding: 0px 5px;">4</li><li style="box-sizing: border-box; padding: 0px 5px;">5</li><li style="box-sizing: border-box; padding: 0px 5px;">6</li><li style="box-sizing: border-box; padding: 0px 5px;">7</li><li style="box-sizing: border-box; padding: 0px 5px;">8</li><li style="box-sizing: border-box; padding: 0px 5px;">9</li><li style="box-sizing: border-box; padding: 0px 5px;">10</li><li style="box-sizing: border-box; padding: 0px 5px;">11</li><li style="box-sizing: border-box; padding: 0px 5px;">12</li><li style="box-sizing: border-box; padding: 0px 5px;">13</li><li style="box-sizing: border-box; padding: 0px 5px;">14</li><li style="box-sizing: border-box; padding: 0px 5px;">15</li><li style="box-sizing: border-box; padding: 0px 5px;">16</li><li style="box-sizing: border-box; padding: 0px 5px;">17</li><li style="box-sizing: border-box; padding: 0px 5px;">18</li><li style="box-sizing: border-box; padding: 0px 5px;">19</li><li style="box-sizing: border-box; padding: 0px 5px;">20</li><li style="box-sizing: border-box; padding: 0px 5px;">21</li><li style="box-sizing: border-box; padding: 0px 5px;">22</li><li style="box-sizing: border-box; padding: 0px 5px;">23</li><li style="box-sizing: border-box; padding: 0px 5px;">24</li><li style="box-sizing: border-box; padding: 0px 5px;">25</li><li style="box-sizing: border-box; padding: 0px 5px;">26</li><li style="box-sizing: border-box; padding: 0px 5px;">27</li><li style="box-sizing: border-box; padding: 0px 5px;">28</li><li style="box-sizing: border-box; padding: 0px 5px;">29</li><li style="box-sizing: border-box; padding: 0px 5px;">30</li><li style="box-sizing: border-box; padding: 0px 5px;">31</li><li style="box-sizing: border-box; padding: 0px 5px;">32</li><li style="box-sizing: border-box; padding: 0px 5px;">33</li><li style="box-sizing: border-box; padding: 0px 5px;">34</li><li style="box-sizing: border-box; padding: 0px 5px;">35</li><li style="box-sizing: border-box; padding: 0px 5px;">36</li><li style="box-sizing: border-box; padding: 0px 5px;">37</li><li style="box-sizing: border-box; padding: 0px 5px;">38</li><li style="box-sizing: border-box; padding: 0px 5px;">39</li><li style="box-sizing: border-box; padding: 0px 5px;">40</li><li style="box-sizing: border-box; padding: 0px 5px;">41</li><li style="box-sizing: border-box; padding: 0px 5px;">42</li><li style="box-sizing: border-box; padding: 0px 5px;">43</li><li style="box-sizing: border-box; padding: 0px 5px;">44</li><li style="box-sizing: border-box; padding: 0px 5px;">45</li><li style="box-sizing: border-box; padding: 0px 5px;">46</li><li style="box-sizing: border-box; padding: 0px 5px;">47</li><li style="box-sizing: border-box; padding: 0px 5px;">48</li><li style="box-sizing: border-box; padding: 0px 5px;">49</li><li style="box-sizing: border-box; padding: 0px 5px;">50</li><li style="box-sizing: border-box; padding: 0px 5px;">51</li><li style="box-sizing: border-box; padding: 0px 5px;">52</li><li style="box-sizing: border-box; padding: 0px 5px;">53</li><li style="box-sizing: border-box; padding: 0px 5px;">54</li><li style="box-sizing: border-box; padding: 0px 5px;">55</li><li style="box-sizing: border-box; padding: 0px 5px;">56</li><li style="box-sizing: border-box; padding: 0px 5px;">57</li><li style="box-sizing: border-box; padding: 0px 5px;">58</li><li style="box-sizing: border-box; padding: 0px 5px;">59</li><li style="box-sizing: border-box; padding: 0px 5px;">60</li><li style="box-sizing: border-box; padding: 0px 5px;">61</li><li style="box-sizing: border-box; padding: 0px 5px;">62</li><li style="box-sizing: border-box; padding: 0px 5px;">63</li><li style="box-sizing: border-box; padding: 0px 5px;">64</li><li style="box-sizing: border-box; padding: 0px 5px;">65</li><li style="box-sizing: border-box; padding: 0px 5px;">66</li><li style="box-sizing: border-box; padding: 0px 5px;">67</li><li style="box-sizing: border-box; padding: 0px 5px;">68</li><li style="box-sizing: border-box; padding: 0px 5px;">69</li><li style="box-sizing: border-box; padding: 0px 5px;">70</li><li style="box-sizing: border-box; padding: 0px 5px;">71</li><li style="box-sizing: border-box; padding: 0px 5px;">72</li><li style="box-sizing: border-box; padding: 0px 5px;">73</li><li style="box-sizing: border-box; padding: 0px 5px;">74</li><li style="box-sizing: border-box; padding: 0px 5px;">75</li><li style="box-sizing: border-box; padding: 0px 5px;">76</li><li style="box-sizing: border-box; padding: 0px 5px;">77</li><li style="box-sizing: border-box; padding: 0px 5px;">78</li><li style="box-sizing: border-box; padding: 0px 5px;">79</li><li style="box-sizing: border-box; padding: 0px 5px;">80</li><li style="box-sizing: border-box; padding: 0px 5px;">81</li><li style="box-sizing: border-box; padding: 0px 5px;">82</li><li style="box-sizing: border-box; padding: 0px 5px;">83</li><li style="box-sizing: border-box; padding: 0px 5px;">84</li><li style="box-sizing: border-box; padding: 0px 5px;">85</li><li style="box-sizing: border-box; padding: 0px 5px;">86</li><li style="box-sizing: border-box; padding: 0px 5px;">87</li><li style="box-sizing: border-box; padding: 0px 5px;">88</li><li style="box-sizing: border-box; padding: 0px 5px;">89</li><li style="box-sizing: border-box; padding: 0px 5px;">90</li><li style="box-sizing: border-box; padding: 0px 5px;">91</li><li style="box-sizing: border-box; padding: 0px 5px;">92</li><li style="box-sizing: border-box; padding: 0px 5px;">93</li><li style="box-sizing: border-box; padding: 0px 5px;">94</li><li style="box-sizing: border-box; padding: 0px 5px;">95</li><li style="box-sizing: border-box; padding: 0px 5px;">96</li><li style="box-sizing: border-box; padding: 0px 5px;">97</li><li style="box-sizing: border-box; padding: 0px 5px;">98</li><li style="box-sizing: border-box; padding: 0px 5px;">99</li><li style="box-sizing: border-box; padding: 0px 5px;">100</li><li style="box-sizing: border-box; padding: 0px 5px;">101</li><li style="box-sizing: border-box; padding: 0px 5px;">102</li><li style="box-sizing: border-box; padding: 0px 5px;">103</li><li style="box-sizing: border-box; padding: 0px 5px;">104</li><li style="box-sizing: border-box; padding: 0px 5px;">105</li><li style="box-sizing: border-box; padding: 0px 5px;">106</li><li style="box-sizing: border-box; padding: 0px 5px;">107</li><li style="box-sizing: border-box; padding: 0px 5px;">108</li><li style="box-sizing: border-box; padding: 0px 5px;">109</li><li style="box-sizing: border-box; padding: 0px 5px;">110</li><li style="box-sizing: border-box; padding: 0px 5px;">111</li><li style="box-sizing: border-box; padding: 0px 5px;">112</li><li style="box-sizing: border-box; padding: 0px 5px;">113</li><li style="box-sizing: border-box; padding: 0px 5px;">114</li><li style="box-sizing: border-box; padding: 0px 5px;">115</li><li style="box-sizing: border-box; padding: 0px 5px;">116</li><li style="box-sizing: border-box; padding: 0px 5px;">117</li><li style="box-sizing: border-box; padding: 0px 5px;">118</li><li style="box-sizing: border-box; padding: 0px 5px;">119</li><li style="box-sizing: border-box; padding: 0px 5px;">120</li><li style="box-sizing: border-box; padding: 0px 5px;">121</li><li style="box-sizing: border-box; padding: 0px 5px;">122</li><li style="box-sizing: border-box; padding: 0px 5px;">123</li><li style="box-sizing: border-box; padding: 0px 5px;">124</li><li style="box-sizing: border-box; padding: 0px 5px;">125</li><li style="box-sizing: border-box; padding: 0px 5px;">126</li><li style="box-sizing: border-box; padding: 0px 5px;">127</li><li style="box-sizing: border-box; padding: 0px 5px;">128</li><li style="box-sizing: border-box; padding: 0px 5px;">129</li><li style="box-sizing: border-box; padding: 0px 5px;">130</li><li style="box-sizing: border-box; padding: 0px 5px;">131</li><li style="box-sizing: border-box; padding: 0px 5px;">132</li><li style="box-sizing: border-box; padding: 0px 5px;">133</li><li style="box-sizing: border-box; padding: 0px 5px;">134</li><li style="box-sizing: border-box; padding: 0px 5px;">135</li><li style="box-sizing: border-box; padding: 0px 5px;">136</li><li style="box-sizing: border-box; padding: 0px 5px;">137</li><li style="box-sizing: border-box; padding: 0px 5px;">138</li><li style="box-sizing: border-box; padding: 0px 5px;">139</li><li style="box-sizing: border-box; padding: 0px 5px;">140</li><li style="box-sizing: border-box; padding: 0px 5px;">141</li><li style="box-sizing: border-box; padding: 0px 5px;">142</li><li style="box-sizing: border-box; padding: 0px 5px;">143</li><li style="box-sizing: border-box; padding: 0px 5px;">144</li><li style="box-sizing: border-box; padding: 0px 5px;">145</li><li style="box-sizing: border-box; padding: 0px 5px;">146</li><li style="box-sizing: border-box; padding: 0px 5px;">147</li><li style="box-sizing: border-box; padding: 0px 5px;">148</li><li style="box-sizing: border-box; padding: 0px 5px;">149</li><li style="box-sizing: border-box; padding: 0px 5px;">150</li></ul>
在这里我们主要分析一下接收数据请求的情况：在这里我们看到了BBinder对象，并调用了它的transact函数，其实在内部调用了onTransact函数，而这个函数在BBinder中只是定义了两种code之下的操作，大部分的情况是由它的子类完成。还记得上一篇中那个类的关系图吗：BBinder的直接子类是BnInterface，而这是一个接口类，所以所有的任务都落在了BnInterface的子类BnServiceManager中。
总结
看了这个类IPCThreadState，真的有点头晕眼花，究其原因是：该类将代码一部分给客户端使用，一部分给服务端使用，所以有点杂乱。总结一下今天学到的IPCThreadState的工作：
- 首先，通过线程本地存储机制IPCThreadState将自身和线程本地存储关联起来；
- 通过writeTransactionData将发生的数据存储在mOut中；
- waitForResponse调用了talkWithDriver从Binder设备中读写数据，在这里采用的是ioctl方式；
- 调用executeCommand函数解析并执行mIn中的数据。
原文地址： http://blog.csdn.net/smbroe/article/details/44725143
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