Android Binder 机制详解
Android Binder 机制详解
- 1、binder原理
- 1.1、IPC函数指针
- 1.2、IPC函数参数
- 1.3、IPC函数返回值
- 1.4、binder内存
- 2、binder驱动
- 2.1、service_manager的初始化
- 2.2、service_server的addService
- 2.3、service_client的get service
- 2.4、service_client调用service
- 2.5、Scatter-gather模式
- 2.6、多个binder context
- 2.7、调试接口
- 3、service manager实现
- 4、native实现
- 4.1、process/thread
- 4.2、manager proxy
- 4.3、server
- 4.4、client proxy
- 4.5、service thread管理
- 4.6、死亡通知(DeathRecipient)
- 5、java实现
- 6、AIDL(Android Interface Definition Language)
- 参考资料:
1、binder原理
纵观现有市面上所有讲binder的文章,都存在一个最大的问题:没有讲清楚binder对象是什么?
不清楚binder对象是什么,那就不能理解handle是什么?不能理解什么时候是binder什么时候是handle,那就不能真正理解整个IPC的通讯过程。
我们首先回到binder的目的,就是IPC(Inter-Process Communication)进程间通讯。那么怎么样实现进程间通讯呢?要素有三个:
- 函数指针;
- 函数参数;
- 函数返回值;
binder通讯的本质实际上非常简单,就是client、server双方在共享内存的基础上封装成自定义api函数,并无神奇之处。我们看看他是怎么和IPC三要素对应上的:
1.1、IPC函数指针
binder的service_server可以向service_client提供service服务,但反过来不行。所以binder service其实是单向的,只有service_server端才能提供service函数,且函数只能在service_server端运行。
大部分情况下:service_server端提供的一组IPC服务本地函数,就是binder对象。
例如,mediaserver注册的一系列service中的一个"media.player":
/frameworks/av/media/mediaserver/main_mediaserver.cpp:
int main(int argc __unused, char **argv __unused)
{MediaPlayerService::instantiate();
}
↓/frameworks/av/media/libmediaplayerservice/MediaPlayerService.cpp:
void MediaPlayerService::instantiate() {defaultServiceManager()->addService(String16("media.player"), new MediaPlayerService());
}
service_server提供了一组可以在server本地运行的函数,即binder对象。如下:
/frameworks/av/media/libmedia/IMediaPlayerService.cpp:
status_t BnMediaPlayerService::onTransact(uint32_t code, const Parcel& data, Parcel* reply, uint32_t flags)
{switch (code) {case CREATE: {CHECK_INTERFACE(IMediaPlayerService, data, reply);sp<IMediaPlayerClient> client =interface_cast<IMediaPlayerClient>(data.readStrongBinder());audio_session_t audioSessionId = (audio_session_t) data.readInt32();sp<IMediaPlayer> player = create(client, audioSessionId);reply->writeStrongBinder(IInterface::asBinder(player));return NO_ERROR;} break;case CREATE_MEDIA_RECORDER: {CHECK_INTERFACE(IMediaPlayerService, data, reply);const String16 opPackageName = data.readString16();sp<IMediaRecorder> recorder = createMediaRecorder(opPackageName);reply->writeStrongBinder(IInterface::asBinder(recorder));return NO_ERROR;} break;...}
}
在service_client端可以通过handle来引用这个binder对象,还封装了一系列与之对应的函数来组织数据。但是这些函数实际上是通讯用的,函数的实际功能并不能在client本地执行:
/frameworks/av/media/libmedia/IMediaPlayerService.cpp:
class BpMediaPlayerService: public BpInterface<IMediaPlayerService>
{
public:virtual sp<IMediaPlayer> create(const sp<IMediaPlayerClient>& client, audio_session_t audioSessionId) {Parcel data, reply;data.writeInterfaceToken(IMediaPlayerService::getInterfaceDescriptor());data.writeStrongBinder(IInterface::asBinder(client));data.writeInt32(audioSessionId);remote()->transact(CREATE, data, &reply);return interface_cast<IMediaPlayer>(reply.readStrongBinder());}virtual sp<IMediaRecorder> createMediaRecorder(const String16 &opPackageName){Parcel data, reply;data.writeInterfaceToken(IMediaPlayerService::getInterfaceDescriptor());data.writeString16(opPackageName);remote()->transact(CREATE_MEDIA_RECORDER, data, &reply);return interface_cast<IMediaRecorder>(reply.readStrongBinder());}...
};
所以理解binder对象和handle是非常关键的。service_server端需要在本地执行函数,所以执行时函数调用的3要素(函数、参数、返回值)都必须是本地的,所以它必须拥有一组函数的binder对象;service_client端不需要在本地执行,所以它没有函数集的binder对象,它只有函数集的远端引用handle。
binder通讯的3个主角:service_mannager、service_server、service_client。在各种场景下,分别的binder对象和handle关系如下:
衍生出的原则如下:
- service_server类的进程只有binder对象,没有handle(除了handle0),因为它所有操作都必须本地执行,引用远程对象毫无意义;
- service_client类的进程只有handle,没有binder对象,因为它需要远程执行service不需要本地执行;
- service_mannager进程同时有binder对象和handle,它本地binder对象的作用就是操作所有其他进程的handle;
1.2、IPC函数参数
如上一节描述,service_client可以通过名字向service_manage查询得到handle。这个handle就相当于远程的函数集指针。
但是对于一个函数调用,我们除了需要函数指针,还需要传递参数。
binder使用parcel方式来打包函数参数和返回值。parcel可以用来传递几种类型的数据:
- 普通类型的少量数据;
- binder对象/handle(struct flat_binder_object);
- fd(struct binder_fd_object);
下面详细描述每种情况的parcel包格式和承载的内容。
- 1、普通类型的少量数据:
这种普通类型(int/long/string…)的少量数据存储最为简单,存入时按照一定的顺序存入,取出时按照数据的排列格式取出即可。
- 2、binder对象/handle(struct flat_binder_object):
这一类型数据的parcel包格式如下:
可以看到这种类型的parcel包中包含了两种数据:data0/data1/…是普通类型数据;binder_obj0/binder_obj1/…是binder对象,binder_obj0 offset/binder_obj1 offset/…指出了了binder对象在parcel包中的偏移;
binder对象和handle共用结构体struct flat_binder_object。
上一节说过binder对象其实就是一组函数的指针,但是一个指针只需要一个long类型就可以标识了,为什么还需要用一个结构体struct flat_binder_object来传递。我理解下来主要的思想如下:使用binder都是面向对象语言c++/java,它们把函数组也要实例化成一个对象,一个对象只有被引用时才不会被回收,远程引用也需要让本地引用加1。
一组service函数,对本地进程来说就是binder,对其他需要使用的进程来说需要远程引用,就是handle,是一对多的关系。关系图如下:
binder object是service_server的一个“local binder object”,service_manager和service_client创建了多个远程引用“remote handle”。
这个其实就是binder的核心思想,binder花费了大量的代码在维护这个关系上面:
- service_server进程在驱动中创建了binder_node节点来保存binder对象,把本进程所有的binder_node都挂载在一颗红黑树proc->nodes上;
- service_manager和service_client每个新进程对这个binder对象引用,就创建一个新的binder_ref,它的值就是handle,并回指向binder_node。并且把本进程对其他service_server的引用都挂载到两颗红黑树proc->refs_by_node/proc->refs_by_desc上。并且远程引用会增加service_server进程关于binder对象的引用计数;
binder驱动负责建立起binder对象和handle之间的映射关系,创建上述的数据结构,并负责翻译:
service_server把本地binder对象向service_manager注册。会在service_manager进程本地建立起binder_node,驱动会在service_manager进程中建立起对应的binder_ref引用,那么service_manager进程能看到的其实就是本进程对service_serverbinder对象的一个引用,并不能看到binder对象原始值;
service_client根据名字向service_manager查询service。service_manager会返回本进程的handle,在内核中该handle会转换成binder对象binder_node。因为service_client不是service的本地进程,所以service_client不能得到binder对象,它只能得到引用handle。所以再针对service的binder对象创建一份service_client进程的本地引用;
service_client调用远程service_server的service。内核判断handle引用是service_server的本地对象,就把handle转换成service_server的binder对象;
3、fd(struct binder_fd_object):
parcel还能传输文件句柄fd,此时的包格式如下:
传输fd的意义何在呢?当binder的两个进程间需要传输大量的数据。例如:图像声音数据、或者是一个对象。可以在匿名共享内存(Ashmem)中创建一块区域,源进程会得到一个相应的fd,再把这个fd使用binder传递给目的进程,就可以共享数据了。
需要特别说明的是对象的传递,在同一个进程内进行函数调用的话,参数对象通常是使用引用的方式传递的。但是如果是跨进程的调用,是没有办法引用的,只有把整个对象复制过去。这种操作叫做对象的序列化,java称为Serializable,android有优化的实现Parcelable。注意对象序列化的Parcelable和binder的parcel数据封装不是一回事,尽管他们原理上很相似。binder并没有提供对象Parcelable的接口,如果我们要跨进程传输对象,只能把对象序列化(Parcelable)到匿名共享内存中,再把对应fd通过binder传输给目的进程。
binder驱动在检测到传输的是fd,会在新的进程中分配一个新的fd,并指向原来的file结构,这样fd就被跨进程duplicate了。两个进程使用各自的fd对匿名共享内存区域进行mmap映射,就能访问相同的内存区域了。
1.3、IPC函数返回值
函数返回值也是使用和函数参数一样的parcel结构来封装数据的。就不再重复叙述。
上面提到的原则需要再次强调,在一次service_client和service_server之间的通讯,在传递参数和返回值时都要遵循的准则:service_client只会有handle,service_server只会有binder对象。
1.4、binder内存
前面说过binder通讯的本质就是在共享内存上加上一层api,我们来看看他是怎么管理共享内存的。
我们可以看到:
- binder驱动给每个进程分配最多4M的buffer空间,这段空间在内核通过binder_proc->alloc红黑树来管理,同时通过mmap映射到进程用户空间;
- 和所有的进程通讯机制类似,这段空间相当于进程的接收邮箱inbox,其他进程发过来的消息会从其他进程用户空间复制存放到这里;
- 因为是mmap的所有本进程的用户空间访问免除了一次拷贝;
- 另外因为进程支持多个线程,所以多个线程会共享本进程的binder buffer;
我们看一下process 0、process n进程和process 1进程进行binder通讯时的buffer使用情况:
- 首先会在process 1进程的inbox(binder buffer)空间中分配buffer;
- binder驱动把process 0、process n进程用户空间的消息拷贝到process 1进程的inbox内核buffer中;
- 因为mmap,process 1进程的用户空间也可以看见这些消息了;
2、binder驱动
驱动是整个binder通讯的核心,java和native都是对其的封装。
因为binder驱动代码比较繁杂,看代码比较不好理解。结合第一章讲的基础知识和binder通讯具体场景,我们使用图来分析每一个典型场景下binder驱动内的变化。
2.1、service_manager的初始化
通过上图我们可以看到具体过程:
- 1、binder驱动为service_manager进程创建一个新的binder_node结构,赋值:.ptr=0、.cookie=0、.proc=当前proc;
- 2、把这个binder_node新节点加入到当前进程的proc->nodes红黑树中;
- 3、把binder_device的全局handle 0指针binder_device->context.binder_context_mgr_node指向新创建的binder_node;这样其他人通过handle 0指针就能找到对应binder_node,进一步找到service_manager是哪一个进程;
service_manager代码在service_manager.c、binder.c,可以具体查看。初始化过程为:
main() -> binder_open()、binder_become_context_manager()
2.2、service_server的addService
通过上图我们可以看到,在service_server向service_manager注册service的时候,在驱动中的具体流程如下:
- 1、因为是向service_manager注册,所以target handle固定=0。通过binder_device->context找到handle 0对应的binder_node,也就找到了对应的binder_proc,找到了对应的service_manager进程;
- 2、在service_manager进程中分配binder buffer,把service_server传递过来的parcel数据全部复制进去;
- 3、翻译parcel数据中的binder对象,把binder翻译成handle;
- 4、可以看到service_manager进程的handle就是对service_server进程binder的一个引用。把handle加入到service_manager进程的handle缓存红黑树中;
- 5、把翻译后的parcel数据和其他信息打包成binder_transaction结构,并挂载到service_manager进程的proc->todo/thread->todo链表中,等待service_manager进程的读取;
service_manager的读取响应和reply动作就不去具体分析了,因为都非常的清晰。service_manager代码在service_manager.c、binder.c,可以具体查看。service_manager在svcmgr_handler()函数中响应service_server的SVC_MGR_ADD_SERVICE请求,最终调用do_add_service()把handle和对应的service name加到svclist链表中:
main() -> binder_loop() -> binder_parse() -> svcmgr_handler() -> do_add_service()
2.3、service_client的get service
如上图service_client向service_manager发送get service请求的数据比较简单:
- 1、根据handle 0找到service_manager进程;
- 2、在service_manager进程中分配binder buffer,把service_client传递过来的parcel数据全部复制进去;
- 3、parcel的内容中没有binder或者handle,不需要翻译;
- 4、把parcel数据和其他信息打包成binder_transaction结构,并挂载到proc->todo/thread->todo链表中,等待service_manager进程的读取;
上图是service_manager给service_client回复信息的过程:
- 1、service_manager根据service name在本地svclist链表中找到对应的handle,它把handle打包进parcel并reply给service_client;
- 2、根据service_manager所在线程thread->transaction_stack字段中保存的binder_transaction结构,从.from字段可以找到service_client所在的线程(binder_thread)和进程(binder_proc);
- 3、在service_client进程中分配binder buffer,把service_manager传递过来的parcel数据全部复制进去;
- 4、翻译parcel中打包的handle结构,判断handle指向的binder_node进程不是service_client进程,所以新建service_client进程中对binder_node新的引用。新创建handle并加入到service_client进程的handle缓存红黑树中;
- 5、这样service_client就从service_manager中获取到了service_server binder对应的引用handle;
- 6、把翻译后的parcel数据和其他信息打包成binder_transaction结构,并挂载到service_client进程的proc->todo/thread->todo链表中,等待service_client进程读取reply;
2.4、service_client调用service
上图是service_client调用service_server的service的过程:
- 1、service_client的target handle为上一步向service_manager查询得到的handle,根据handle能找到对应binder_node,进一步找到service_server所在进程;
- 2、在service_server进程中分配binder buffer,把service_client传递过来的parcel数据全部复制进去;
- 3、parcel中打包了函数参数,如果包含handle对象,需要进行翻译;不可能包含binder对象,因为service_client进程的binder对象在service_server进程中无法运行;
- 4、如果parcel中包含的handle指向的binder_noe和service_server是同一进程,把它翻译成本地binder,在本地可以运行;
- 5、如果parcel中包含的handle指向的binder_noe和service_server不是同一进程,那只能在service_server进程中给它创建一份新的引用handle。这个handle也不能在service_server进程中运行,只能向其他service_server请求服务;
- 6、把翻译后的parcel数据和其他信息打包成binder_transaction结构,并挂载到service_client进程的proc->todo/thread->todo链表中,等待service_client进程读取reply;
2.5、Scatter-gather模式
在Android O中binder增加了一种性能改进模式Scatter-gather,这是因为binder在传输IPC参数数据时,因为传输的量不大,binder实际上做了3次拷贝:
Scatter-gather把3次copy优化成1次:
具体的代码可以看驱动对BINDER_TYPE_PTR类型数据的处理:
case BINDER_TYPE_PTR: {struct binder_buffer_object *bp =to_binder_buffer_object(hdr);size_t buf_left = sg_buf_end - sg_bufp;if (bp->length > buf_left) {binder_user_error("%d:%d got transaction with too large buffer\n",proc->pid, thread->pid);return_error = BR_FAILED_REPLY;return_error_param = -EINVAL;return_error_line = __LINE__;goto err_bad_offset;}if (copy_from_user(sg_bufp,(const void __user *)(uintptr_t)bp->buffer, bp->length)) {binder_user_error("%d:%d got transaction with invalid offsets ptr\n",proc->pid, thread->pid);return_error_param = -EFAULT;return_error = BR_FAILED_REPLY;return_error_line = __LINE__;goto err_copy_data_failed;}/* Fixup buffer pointer to target proc address space */bp->buffer = (uintptr_t)sg_bufp +binder_alloc_get_user_buffer_offset(&target_proc->alloc);sg_bufp += ALIGN(bp->length, sizeof(u64));ret = binder_fixup_parent(t, thread, bp, off_start,offp - off_start,last_fixup_obj,last_fixup_min_off);if (ret < 0) {return_error = BR_FAILED_REPLY;return_error_param = ret;return_error_line = __LINE__;goto err_translate_failed;}last_fixup_obj = bp;last_fixup_min_off = 0;} break;
2.6、多个binder context
Android O以后创建了3个misc设备,对应3个domain(contexts),相互独立:
# ls /dev/*binder
/dev/binder /dev/hwbinder /dev/vndbinder
因为在Android O以后HIDL也启用了binder通信,使用binder通信的进程越来越多,为了便于管理并且相互隔离,Android把binder划分成了3个domain(contexts):
IPC Domain | Description |
---|---|
/dev/binder | IPC between framework/app processes with AIDL interfaces |
/dev/hwbinder | IPC between framework/vendor processes with HIDL interfacesIPC between vendor processes with HIDL interfaces |
/dev/vndbinder | IPC between vendor/vendor processes with AIDL Interfaces |
2.7、调试接口
binder驱动创建了很多调试接口,可以方便的debug binder通讯的过程。
1、"/d/binder/state"
全局情况:
# more /d/binder/state
binder state:
dead nodes:node 392820: u0000007b50bf75a0 c0000007b2b4d5b80 pri 0:139 hs 1 hw 1 ls 0 lw 0is 1 iw 1 tr 1 proc 3021node 176573: u0000007b50bf72c0 c0000007b4515a600 pri 0:139 hs 1 hw 1 ls 0 lw 0is 1 iw 1 tr 1 proc 5571node 56178: u0000007b50a8dfa0 c0000007b50bc31c0 pri 0:139 hs 1 hw 1 ls 0 lw 0
is 1 iw 1 tr 1 proc 3135node 47334: u0000007b47f0df40 c0000007b47f077c0 pri 0:139 hs 1 hw 1 ls 0 lw 0
is 1 iw 1 tr 1 proc 1458node 342153: u0000007b47f0d480 c0000007b451bf8c0 pri 0:139 hs 1 hw 1 ls 0 lw 0is 1 iw 1 tr 1 proc 5571node 50574: u0000007b451ffa20 c0000007b3519e5c0 pri 0:139 hs 1 hw 1 ls 0 lw 0
is 1 iw 1 tr 1 proc 1458node 49594: u0000007b451ff940 c0000007b3507f480 pri 0:139 hs 1 hw 1 ls 0 lw 0
is 1 iw 1 tr 1 proc 2859
2、"/d/binder/stats"
全局统计:
# more /d/binder/stats
binder stats:
BC_TRANSACTION: 226132
BC_REPLY: 201918
BC_FREE_BUFFER: 633493
BC_INCREFS: 9234
BC_ACQUIRE: 9415
BC_RELEASE: 6040
BC_DECREFS: 6014
BC_INCREFS_DONE: 5551
BC_ACQUIRE_DONE: 5552
BC_REGISTER_LOOPER: 355
BC_ENTER_LOOPER: 229
BC_REQUEST_DEATH_NOTIFICATION: 2908
BC_CLEAR_DEATH_NOTIFICATION: 2146
BC_DEAD_BINDER_DONE: 225
BC_TRANSACTION_SG: 118790
BC_REPLY_SG: 86885
BR_TRANSACTION: 344921
BR_REPLY: 288803
BR_TRANSACTION_COMPLETE: 633725
BR_INCREFS: 5559
BR_ACQUIRE: 5560
BR_RELEASE: 3436
BR_DECREFS: 3435
BR_SPAWN_LOOPER: 357
BR_DEAD_BINDER: 226
BR_CLEAR_DEATH_NOTIFICATION_DONE: 2146
proc: active 163 total 232
thread: active 852 total 3214
node: active 1610 total 5564
ref: active 2557 total 9384
death: active 746 total 2908
transaction: active 1 total 633725
transaction_complete: active 0 total 633725
proc 10578
context binderthreads: 18requested threads: 0+2/15ready threads 3free async space 520192nodes: 41
3、"/d/binder/proc/xxx"
具体进程的情况:
# cat /d/binder/proc/1037
binder proc state:
proc 1037
context binderthread 1037: l 12 need_return 0 tr 0thread 1094: l 00 need_return 0 tr 0thread 1096: l 12 need_return 0 tr 0node 2758: u0000006fe9c10000 c0000006fe9c0d008 pri 0:139 hs 1 hw 1 ls 0 lw 0 is 1 iw 1 tr 1 proc 704node 1192: u0000006fea02f620 c0000006fea029868 pri 0:139 hs 1 hw 1 ls 0 lw 0 is 1 iw 1 tr 1 proc 549ref 1190: desc 0 node 2 s 1 w 1 d 0000000000000000ref 1204: desc 1 node 170 s 1 w 1 d 0000000000000000ref 249105: desc 2 node 5946 s 1 w 1 d 0000000000000000buffer 249107: 0000000000000000 size 3600:0:0 delivered
3、service manager实现
service_manager逻辑很清晰,代码也不多,主要流程在上节中已经描述就不再详细分析。service_manager.c、binder.c
4、native实现
整个native层binder的实现还是以mediaserver为例来说明。
4.1、process/thread
上图已经把native层binder通讯最重要的部分都画出来了,理解了这张图native的实现基本理解了大半:
binder在server接收端会创建多个线程,在发送端不会创建专门的线程直接在发送者的线程中;
binder在server端的通用对象是BBinder,在client端的通用引用对象是BpBinder。具体service的server端和client端的实现,只要继承这两个类就行了;
1、ProcessState类
因为binder buffer是一个进程一份的,所以不论是client还是server进程,都只会创建一个binder fd,进行一次mmap映射。binder fd、mmap公共资源在本进程内的多个线程间共享。native使用了一个ProcessState类来管理这些进程公共资源。
sp<ProcessState> proc(ProcessState::self());
↓
frameworks/native/libs/binder/ProcessState.cpp:
sp<ProcessState> ProcessState::self()
{Mutex::Autolock _l(gProcessMutex);if (gProcess != NULL) {return gProcess;}/* (1) 创建新的ProcessState对象 */gProcess = new ProcessState("/dev/binder");return gProcess;
}
↓
ProcessState::ProcessState(const char *driver): mDriverName(String8(driver)), mDriverFD(open_driver(driver)) /* (1.1) open binder节点"/dev/binder",获得文件句柄 */, mVMStart(MAP_FAILED), mThreadCountLock(PTHREAD_MUTEX_INITIALIZER), mThreadCountDecrement(PTHREAD_COND_INITIALIZER), mExecutingThreadsCount(0), mMaxThreads(DEFAULT_MAX_BINDER_THREADS), mStarvationStartTimeMs(0), mManagesContexts(false), mBinderContextCheckFunc(NULL), mBinderContextUserData(NULL), mThreadPoolStarted(false), mThreadPoolSeq(1)
{if (mDriverFD >= 0) {// mmap the binder, providing a chunk of virtual address space to receive transactions./* (1.2) 根据fd映射1M的mmap空间 */mVMStart = mmap(0, BINDER_VM_SIZE, PROT_READ, MAP_PRIVATE | MAP_NORESERVE, mDriverFD, 0);if (mVMStart == MAP_FAILED) {// *sigh*ALOGE("Using /dev/binder failed: unable to mmap transaction memory.\n");close(mDriverFD);mDriverFD = -1;mDriverName.clear();}}LOG_ALWAYS_FATAL_IF(mDriverFD < 0, "Binder driver could not be opened. Terminating.");
}
↓
static int open_driver(const char *driver)
{/* (1.1.1) open节点的具体操作 */int fd = open(driver, O_RDWR | O_CLOEXEC);if (fd >= 0) {int vers = 0;status_t result = ioctl(fd, BINDER_VERSION, &vers);if (result == -1) {ALOGE("Binder ioctl to obtain version failed: %s", strerror(errno));close(fd);fd = -1;}if (result != 0 || vers != BINDER_CURRENT_PROTOCOL_VERSION) {ALOGE("Binder driver protocol(%d) does not match user space protocol(%d)! ioctl() return value: %d",vers, BINDER_CURRENT_PROTOCOL_VERSION, result);close(fd);fd = -1;}/* (1.1.2) 设置默认最大接收线程数为15 */size_t maxThreads = DEFAULT_MAX_BINDER_THREADS;result = ioctl(fd, BINDER_SET_MAX_THREADS, &maxThreads);if (result == -1) {ALOGE("Binder ioctl to set max threads failed: %s", strerror(errno));}} else {ALOGW("Opening '%s' failed: %s\n", driver, strerror(errno));}return fd;
}
- 2、IPCThreadState类
native binder对线程也进行了封装。
- 2.1、对于server端来说,native binder创建一个线程池,可以多个接收线程来响应和运行service服务。例如
# ps -eT | grep Binder
mediaex 1028 1180 1 2179292 15664 binder_thread_read 0 S Binder:1028_1
mediaex 1028 1886 1 2179292 15664 binder_thread_read 0 S Binder:1028_2
mediaex 1028 1887 1 2179292 15664 binder_thread_read 0 S Binder:1028_3
mediaex 1028 2489 1 2179292 15664 binder_thread_read 0 S Binder:1028_4
mediaex 1028 5497 1 2179292 15664 binder_thread_read 0 S Binder:1028_5
media 1034 1130 1 2140724 10968 binder_thread_read 0 S Binder:1034_1
media 1034 8000 1 2140724 10968 binder_thread_read 0 S Binder:1034_2
具体代码如下:
ProcessState::self()->startThreadPool();
↓
void ProcessState::startThreadPool()
{AutoMutex _l(mLock);if (!mThreadPoolStarted) {mThreadPoolStarted = true;spawnPooledThread(true);}
}
↓
void ProcessState::spawnPooledThread(bool isMain)
{if (mThreadPoolStarted) {String8 name = makeBinderThreadName();ALOGV("Spawning new pooled thread, name=%s\n", name.string());/* (1)新创建一个PoolThread对象 main的意思就是它是一个接收主线程,它不会动态的退出*/sp<Thread> t = new PoolThread(isMain);t->run(name.string());}
}
↓
PoolThread类继承了Thread类,并且实现了线程主循环函数:threadLoop()
class PoolThread : public Thread
{
public:explicit PoolThread(bool isMain): mIsMain(isMain){}protected:virtual bool threadLoop(){/* (1.1) 线程主循环,进一步调用 */IPCThreadState::self()->joinThreadPool(mIsMain);return false;}const bool mIsMain;
};
↓
创建IPCThreadState对象
frameworks/native/libs/binder/IPCThreadState.cpp:
IPCThreadState* IPCThreadState::self()
{if (gHaveTLS) {
restart:const pthread_key_t k = gTLS;IPCThreadState* st = (IPCThreadState*)pthread_getspecific(k);if (st) return st;/* (1.1.1) 创建一个本地线程的IPCThreadState对象 */return new IPCThreadState;}if (gShutdown) {ALOGW("Calling IPCThreadState::self() during shutdown is dangerous, expect a crash.\n");return NULL;}pthread_mutex_lock(&gTLSMutex);if (!gHaveTLS) {int key_create_value = pthread_key_create(&gTLS, threadDestructor);if (key_create_value != 0) {pthread_mutex_unlock(&gTLSMutex);ALOGW("IPCThreadState::self() unable to create TLS key, expect a crash: %s\n",strerror(key_create_value));return NULL;}gHaveTLS = true;}pthread_mutex_unlock(&gTLSMutex);goto restart;
}
↓
IPCThreadState::IPCThreadState(): mProcess(ProcessState::self()),mStrictModePolicy(0),mLastTransactionBinderFlags(0)
{pthread_setspecific(gTLS, this);clearCaller();// FLYME:duanlusheng@SHELL.Flyme.hips.Feature {@mRealCallingPid = -1;// @}mIn.setDataCapacity(256);mOut.setDataCapacity(256);
}
↓
最后进入IPCThreadState类的线程主循环函数joinThreadPool()
void IPCThreadState::joinThreadPool(bool isMain)
{LOG_THREADPOOL("**** THREAD %p (PID %d) IS JOINING THE THREAD POOL\n", (void*)pthread_self(), getpid());mOut.writeInt32(isMain ? BC_ENTER_LOOPER : BC_REGISTER_LOOPER);status_t result;do {processPendingDerefs();// now get the next command to be processed, waiting if necessaryresult = getAndExecuteCommand();if (result < NO_ERROR && result != TIMED_OUT && result != -ECONNREFUSED && result != -EBADF) {ALOGE("getAndExecuteCommand(fd=%d) returned unexpected error %d, aborting",mProcess->mDriverFD, result);abort();}// Let this thread exit the thread pool if it is no longer// needed and it is not the main process thread.if(result == TIMED_OUT && !isMain) {break;}} while (result != -ECONNREFUSED && result != -EBADF);LOG_THREADPOOL("**** THREAD %p (PID %d) IS LEAVING THE THREAD POOL err=%d\n",(void*)pthread_self(), getpid(), result);mOut.writeInt32(BC_EXIT_LOOPER);talkWithDriver(false);
}
↓
status_t IPCThreadState::getAndExecuteCommand()
{status_t result;int32_t cmd;/* (1.1.2.1) 和binder驱动交互:把mOut中的数据发送给binder驱动把接收驱动中的数据到mIn*/result = talkWithDriver();if (result >= NO_ERROR) {size_t IN = mIn.dataAvail();if (IN < sizeof(int32_t)) return result;/* (1.1.2.2) 读出接收数据中的cmd */cmd = mIn.readInt32();IF_LOG_COMMANDS() {alog << "Processing top-level Command: "<< getReturnString(cmd) << endl;}pthread_mutex_lock(&mProcess->mThreadCountLock);mProcess->mExecutingThreadsCount++;if (mProcess->mExecutingThreadsCount >= mProcess->mMaxThreads &&mProcess->mStarvationStartTimeMs == 0) {mProcess->mStarvationStartTimeMs = uptimeMillis();}pthread_mutex_unlock(&mProcess->mThreadCountLock);/* (1.1.2.3) 执行cmd */result = executeCommand(cmd);pthread_mutex_lock(&mProcess->mThreadCountLock);mProcess->mExecutingThreadsCount--;if (mProcess->mExecutingThreadsCount < mProcess->mMaxThreads &&mProcess->mStarvationStartTimeMs != 0) {int64_t starvationTimeMs = uptimeMillis() - mProcess->mStarvationStartTimeMs;if (starvationTimeMs > 100) {ALOGE("binder thread pool (%zu threads) starved for %" PRId64 " ms",mProcess->mMaxThreads, starvationTimeMs);}mProcess->mStarvationStartTimeMs = 0;}pthread_cond_broadcast(&mProcess->mThreadCountDecrement);pthread_mutex_unlock(&mProcess->mThreadCountLock);}return result;
}
↓
我们只需要关注其中BR_TRANSACTION命令的处理:
status_t IPCThreadState::executeCommand(int32_t cmd)
{BBinder* obj;RefBase::weakref_type* refs;status_t result = NO_ERROR;switch ((uint32_t)cmd) {case BR_TRANSACTION:{binder_transaction_data tr;result = mIn.read(&tr, sizeof(tr));ALOG_ASSERT(result == NO_ERROR,"Not enough command data for brTRANSACTION");if (result != NO_ERROR) break;Parcel buffer;buffer.ipcSetDataReference(reinterpret_cast<const uint8_t*>(tr.data.ptr.buffer),tr.data_size,reinterpret_cast<const binder_size_t*>(tr.data.ptr.offsets),tr.offsets_size/sizeof(binder_size_t), freeBuffer, this);const pid_t origPid = mCallingPid;// FLYME:duanlusheng@SHELL.Flyme.hips.Feature {@const pid_t origPidCopy = mRealCallingPid;// @}const uid_t origUid = mCallingUid;const int32_t origStrictModePolicy = mStrictModePolicy;const int32_t origTransactionBinderFlags = mLastTransactionBinderFlags;mCallingPid = tr.sender_pid;// FLYME:duanlusheng@SHELL.Flyme.hips.Feature {@mRealCallingPid = tr.sender_pid;// @}mCallingUid = tr.sender_euid;mLastTransactionBinderFlags = tr.flags;//ALOGI(">>>> TRANSACT from pid %d uid %d\n", mCallingPid, mCallingUid);Parcel reply;status_t error;IF_LOG_TRANSACTIONS() {TextOutput::Bundle _b(alog);alog << "BR_TRANSACTION thr " << (void*)pthread_self()<< " / obj " << tr.target.ptr << " / code "<< TypeCode(tr.code) << ": " << indent << buffer<< dedent << endl<< "Data addr = "<< reinterpret_cast<const uint8_t*>(tr.data.ptr.buffer)<< ", offsets addr="<< reinterpret_cast<const size_t*>(tr.data.ptr.offsets) << endl;}if (tr.target.ptr) {// We only have a weak reference on the target object, so we must first try to// safely acquire a strong reference before doing anything else with it.if (reinterpret_cast<RefBase::weakref_type*>(tr.target.ptr)->attemptIncStrong(this)) {/* (1.1.2.3.1) 如果target是一个合法的本地对象, 把tr.cookie转换成BBinder对象,并调用BBinder->transact()来处理数据*/error = reinterpret_cast<BBinder*>(tr.cookie)->transact(tr.code, buffer,&reply, tr.flags);reinterpret_cast<BBinder*>(tr.cookie)->decStrong(this);} else {error = UNKNOWN_TRANSACTION;}} else {error = the_context_object->transact(tr.code, buffer, &reply, tr.flags);}//ALOGI("<<<< TRANSACT from pid %d restore pid %d uid %d\n",// mCallingPid, origPid, origUid);if ((tr.flags & TF_ONE_WAY) == 0) {LOG_ONEWAY("Sending reply to %d!", mCallingPid);if (error < NO_ERROR) reply.setError(error);sendReply(reply, 0);} else {LOG_ONEWAY("NOT sending reply to %d!", mCallingPid);}mCallingPid = origPid;// FLYME:duanlusheng@SHELL.Flyme.hips.Feature {@mRealCallingPid = origPidCopy;// @}mCallingUid = origUid;mStrictModePolicy = origStrictModePolicy;mLastTransactionBinderFlags = origTransactionBinderFlags;IF_LOG_TRANSACTIONS() {TextOutput::Bundle _b(alog);alog << "BC_REPLY thr " << (void*)pthread_self() << " / obj "<< tr.target.ptr << ": " << indent << reply << dedent << endl;}}break;}
↓
BBinder是一个标准的通用binder对象,它的transact()函数会被具体的service子类重写,所以会调用到具体子类的transact()函数中
frameworks/native/libs/binder/Binder.cpp:
status_t BBinder::onTransact(uint32_t code, const Parcel& data, Parcel* reply, uint32_t /*flags*/)
{switch (code) {case INTERFACE_TRANSACTION:reply->writeString16(getInterfaceDescriptor());return NO_ERROR;default:return UNKNOWN_TRANSACTION;}
}
↓
BnMediaPlayerService是负责具体实现的子类,最后会调用进BnMediaPlayerService类的onTransact()函数中:
frameworks/av/media/libmedia/IMediaPlayerService.cpp:
status_t BnMediaPlayerService::onTransact(uint32_t code, const Parcel& data, Parcel* reply, uint32_t flags)
{switch (code) {case CREATE: {CHECK_INTERFACE(IMediaPlayerService, data, reply);sp<IMediaPlayerClient> client =interface_cast<IMediaPlayerClient>(data.readStrongBinder());audio_session_t audioSessionId = (audio_session_t) data.readInt32();sp<IMediaPlayer> player = create(client, audioSessionId);reply->writeStrongBinder(IInterface::asBinder(player));return NO_ERROR;} break;case CREATE_MEDIA_RECORDER: {CHECK_INTERFACE(IMediaPlayerService, data, reply);const String16 opPackageName = data.readString16();sp<IMediaRecorder> recorder = createMediaRecorder(opPackageName);reply->writeStrongBinder(IInterface::asBinder(recorder));return NO_ERROR;} break;default:return BBinder::onTransact(code, data, reply, flags);}
}
- 2.2、对于client端来说是发送数据,native binder不会对其创建新的线程,但是IPCThreadState类也为client端的发送提供了封装。
client端通用的binder远端代理类为BpBinder,它的发送数据到binder驱动的函数为transact():
frameworks/native/libs/binder/BpBinder.cpp:
status_t BpBinder::transact(uint32_t code, const Parcel& data, Parcel* reply, uint32_t flags)
{// Once a binder has died, it will never come back to life.if (mAlive) {status_t status = IPCThreadState::self()->transact(mHandle, code, data, reply, flags);if (status == DEAD_OBJECT) mAlive = 0;return status;}return DEAD_OBJECT;
}
↓
最后调用到IPCThreadState类的相关方法:
frameworks/native/libs/binder/IPCThreadState.cpp
status_t IPCThreadState::transact(int32_t handle,uint32_t code, const Parcel& data,Parcel* reply, uint32_t flags)
{status_t err = data.errorCheck();flags |= TF_ACCEPT_FDS;IF_LOG_TRANSACTIONS() {TextOutput::Bundle _b(alog);alog << "BC_TRANSACTION thr " << (void*)pthread_self() << " / hand "<< handle << " / code " << TypeCode(code) << ": "<< indent << data << dedent << endl;}if (err == NO_ERROR) {LOG_ONEWAY(">>>> SEND from pid %d uid %d %s", getpid(), getuid(),(flags & TF_ONE_WAY) == 0 ? "READ REPLY" : "ONE WAY");/* (1) 把数据写入mOut */err = writeTransactionData(BC_TRANSACTION, flags, handle, code, data, NULL);}if (err != NO_ERROR) {if (reply) reply->setError(err);return (mLastError = err);}if ((flags & TF_ONE_WAY) == 0) {#if 0if (code == 4) { // relayoutALOGI(">>>>>> CALLING transaction 4");} else {ALOGI(">>>>>> CALLING transaction %d", code);}#endif/* (2) 使用mOut、mIn和binder驱动进行通讯 */if (reply) {err = waitForResponse(reply);} else {Parcel fakeReply;err = waitForResponse(&fakeReply);}#if 0if (code == 4) { // relayoutALOGI("<<<<<< RETURNING transaction 4");} else {ALOGI("<<<<<< RETURNING transaction %d", code);}#endifIF_LOG_TRANSACTIONS() {TextOutput::Bundle _b(alog);alog << "BR_REPLY thr " << (void*)pthread_self() << " / hand "<< handle << ": ";if (reply) alog << indent << *reply << dedent << endl;else alog << "(none requested)" << endl;}} else {err = waitForResponse(NULL, NULL);}return err;
}↓status_t IPCThreadState::waitForResponse(Parcel *reply, status_t *acquireResult)
{uint32_t cmd;int32_t err;while (1) {/* (2.1) 和binder驱动通讯 */if ((err=talkWithDriver()) < NO_ERROR) break;err = mIn.errorCheck();if (err < NO_ERROR) break;if (mIn.dataAvail() == 0) continue;cmd = (uint32_t)mIn.readInt32();IF_LOG_COMMANDS() {alog << "Processing waitForResponse Command: "<< getReturnString(cmd) << endl;}switch (cmd) {case BR_TRANSACTION_COMPLETE:if (!reply && !acquireResult) goto finish;break;}
4.2、manager proxy
service_client service_server和service_manager通讯时,都是处于client角色,所以只能操作service_manager的代理对象。我们看一下具体的代理对象是怎么创建起来的。
server在注册service服务时,都需要获取到默认manager代理:
void MediaPlayerService::instantiate() {defaultServiceManager()->addService(String16("media.player"), new MediaPlayerService());
}
↓
frameworks/native/libs/binder/IServiceManager.cpp:
sp<IServiceManager> defaultServiceManager()
{if (gDefaultServiceManager != NULL) return gDefaultServiceManager;{AutoMutex _l(gDefaultServiceManagerLock);while (gDefaultServiceManager == NULL) {/* (1) 创建BpBinder对象,并在此基础上创建它的子类BpServiceManager对象 */gDefaultServiceManager = interface_cast<IServiceManager>(ProcessState::self()->getContextObject(NULL));if (gDefaultServiceManager == NULL)sleep(1);}}return gDefaultServiceManager;
}
|→
frameworks/native/libs/binder/ProcessState.cpp
sp<IBinder> ProcessState::getContextObject(const sp<IBinder>& /*caller*/)
{/* (1.1) 为service_manager创建handle=0的BpBinder对象 */return getStrongProxyForHandle(0);
}sp<IBinder> ProcessState::getStrongProxyForHandle(int32_t handle)
{sp<IBinder> result;AutoMutex _l(mLock);/* (1.1.1) 查询BpBinder对象缓存,相同handle是否已经创建 */handle_entry* e = lookupHandleLocked(handle);if (e != NULL) {// We need to create a new BpBinder if there isn't currently one, OR we// are unable to acquire a weak reference on this current one. See comment// in getWeakProxyForHandle() for more info about this.IBinder* b = e->binder;if (b == NULL || !e->refs->attemptIncWeak(this)) {if (handle == 0) {// Special case for context manager...// The context manager is the only object for which we create// a BpBinder proxy without already holding a reference.// Perform a dummy transaction to ensure the context manager// is registered before we create the first local reference// to it (which will occur when creating the BpBinder).// If a local reference is created for the BpBinder when the// context manager is not present, the driver will fail to// provide a reference to the context manager, but the// driver API does not return status.//// Note that this is not race-free if the context manager// dies while this code runs.//// TODO: add a driver API to wait for context manager, or// stop special casing handle 0 for context manager and add// a driver API to get a handle to the context manager with// proper reference counting.Parcel data;status_t status = IPCThreadState::self()->transact(0, IBinder::PING_TRANSACTION, data, NULL, 0);if (status == DEAD_OBJECT)return NULL;}/* (1.1.2) 给新handle新创建一个对应BpBinder对象 */b = new BpBinder(handle);e->binder = b;if (b) e->refs = b->getWeakRefs();result = b;} else {// This little bit of nastyness is to allow us to add a primary// reference to the remote proxy when this team doesn't have one// but another team is sending the handle to us.result.force_set(b);e->refs->decWeak(this);}}return result;
}
|→
在创建完标准BpBinder对象以后,使用了一个模板函数interface_cast()把子类对象也给创建了。interface_cast()的定义在
frameworks/native/libs/binder/include/binder/IInterface.h:
template<typename INTERFACE>
inline sp<INTERFACE> interface_cast(const sp<IBinder>& obj)
{return INTERFACE::asInterface(obj);
}
interface_cast()扩展为:
inline sp<IServiceManager> interface_cast(const sp<IBinder>& obj)
{return IServiceManager::asInterface(obj);
}
frameworks/native/libs/binder/include/binder/IInterface.h:
#define IMPLEMENT_META_INTERFACE(INTERFACE, NAME) \const ::android::String16 I##INTERFACE::descriptor(NAME); \const ::android::String16& \I##INTERFACE::getInterfaceDescriptor() const { \return I##INTERFACE::descriptor; \} \::android::sp<I##INTERFACE> I##INTERFACE::asInterface( \const ::android::sp<::android::IBinder>& obj) \{ \::android::sp<I##INTERFACE> intr; \if (obj != NULL) { \intr = static_cast<I##INTERFACE*>( \obj->queryLocalInterface( \I##INTERFACE::descriptor).get()); \if (intr == NULL) { \intr = new Bp##INTERFACE(obj); \} \} \return intr; \} \I##INTERFACE::I##INTERFACE() { } \I##INTERFACE::~I##INTERFACE() { } \
frameworks/native/libs/binder/IServiceManager.cpp:
IMPLEMENT_META_INTERFACE(ServiceManager, "android.os.IServiceManager");
扩展为:
#define IMPLEMENT_META_INTERFACE(ServiceManager, "android.os.IServiceManager") \const ::android::String16 IServiceManager::descriptor("android.os.IServiceManager"); \const ::android::String16& \IServiceManager::getInterfaceDescriptor() const { \return IServiceManager::descriptor; \} \::android::sp<IServiceManager> IServiceManager::asInterface( \const ::android::sp<::android::IBinder>& obj) \{ \::android::sp<IServiceManager> intr; \if (obj != NULL) { \intr = static_cast<IServiceManager*>( \obj->queryLocalInterface( \IServiceManager::descriptor).get()); \if (intr == NULL) { \intr = new BpServiceManager(obj); \} \} \return intr; \} \IServiceManager::IServiceManager() { } \IServiceManager::~IServiceManager() { } \
所以defaultServiceManager()最后得到了一个BpServiceManager对象,利用它的::addService()方法来注册service。
frameworks/native/libs/binder/IServiceManager.cpp:
class BpServiceManager : public BpInterface<IServiceManager>
{
public:explicit BpServiceManager(const sp<IBinder>& impl): BpInterface<IServiceManager>(impl){}virtual status_t addService(const String16& name, const sp<IBinder>& service,bool allowIsolated){Parcel data, reply;data.writeInterfaceToken(IServiceManager::getInterfaceDescriptor());data.writeString16(name);data.writeStrongBinder(service);data.writeInt32(allowIsolated ? 1 : 0);status_t err = remote()->transact(ADD_SERVICE_TRANSACTION, data, &reply);return err == NO_ERROR ? reply.readExceptionCode() : err;}virtual sp<IBinder> checkService( const String16& name) const{Parcel data, reply;data.writeInterfaceToken(IServiceManager::getInterfaceDescriptor());data.writeString16(name);remote()->transact(CHECK_SERVICE_TRANSACTION, data, &reply);return reply.readStrongBinder();}
remote()->transact()会调用到BpBinder的transact()函数,最后IPCThreadState的transact()函数。
frameworks/native/libs/binder/BpBinder.cpp:
status_t BpBinder::transact(uint32_t code, const Parcel& data, Parcel* reply, uint32_t flags)
{// Once a binder has died, it will never come back to life.if (mAlive) {status_t status = IPCThreadState::self()->transact(mHandle, code, data, reply, flags);if (status == DEAD_OBJECT) mAlive = 0;return status;}return DEAD_OBJECT;
}
借用老罗的一张图总结,service_manager类之间复杂的关系:
4.3、server
有了manager的代理对象以后,server就可以注册服务并且创建binder rx服务线程了。
frameworks/av/media/mediaserver/main_mediaserver.cpp:
int main(int argc __unused, char **argv __unused)
{signal(SIGPIPE, SIG_IGN);sp<ProcessState> proc(ProcessState::self());sp<IServiceManager> sm(defaultServiceManager());ALOGI("ServiceManager: %p", sm.get());InitializeIcuOrDie();MediaPlayerService::instantiate();ResourceManagerService::instantiate();registerExtensions();ProcessState::self()->startThreadPool();IPCThreadState::self()->joinThreadPool();
}
↓
frameworks/av/media/libmediaplayerservice/MediaPlayerService.cpp:
void MediaPlayerService::instantiate() {defaultServiceManager()->addService(String16("media.player"), new MediaPlayerService());
}
所有的细节在上面几节都已经描述过了,还是借用老罗的一张图总结service_server类之间复杂的关系:
4.4、client proxy
service_client也是创建代理对象,和manager代理非常相似。我们也来具体分析一下。
frameworks/av/media/libmedia/IMediaDeathNotifier.cpp:
IMediaDeathNotifier::getMediaPlayerService()
{ALOGV("getMediaPlayerService");Mutex::Autolock _l(sServiceLock);if (sMediaPlayerService == 0) {/* (1) 创建manager代理对象 */sp<IServiceManager> sm = defaultServiceManager();sp<IBinder> binder;do {/* (2) 使用manager代理获取到service的handle, 并根据handle创建一个BpBinder对象*/binder = sm->getService(String16("media.player"));if (binder != 0) {break;}ALOGW("Media player service not published, waiting...");usleep(500000); // 0.5 s} while (true);if (sDeathNotifier == NULL) {sDeathNotifier = new DeathNotifier();}binder->linkToDeath(sDeathNotifier);/* (3) 根据BpBinder对象,使用interface_cast<IMediaPlayerService>()函数创建一个BpMediaPlayerService对象 */sMediaPlayerService = interface_cast<IMediaPlayerService>(binder);}ALOGE_IF(sMediaPlayerService == 0, "no media player service!?");return sMediaPlayerService;
}
有了BpMediaPlayerService对象,即MediaPlayerService的远端代理,就可以调用远端service服务了。
frameworks/wilhelm/src/android/android_LocAVPlayer.cpp:
void LocAVPlayer::onPrepare() {SL_LOGD("LocAVPlayer::onPrepare()");/* (4.1) 获取到MediaPlayerService的远端代理 */sp<IMediaPlayerService> mediaPlayerService(getMediaPlayerService());if (mediaPlayerService != NULL) {switch (mDataLocatorType) {case kDataLocatorUri:/* (4.2) 调用远端service服务 */mPlayer = mediaPlayerService->create(mPlayerClient /*IMediaPlayerClient*/,mPlaybackParams.sessionId);
其中通过sm->getService(String16(“media.player”))返回BpBinder的过程如下:
frameworks/native/libs/binder/IServiceManager.cpp:
virtual sp<IBinder> getService(const String16& name) const{}
↓virtual sp<IBinder> checkService( const String16& name) const{Parcel data, reply;data.writeInterfaceToken(IServiceManager::getInterfaceDescriptor());data.writeString16(name);/* (2.1) 向远程manager查询handle */remote()->transact(CHECK_SERVICE_TRANSACTION, data, &reply);return reply.readStrongBinder();}
↓
frameworks/native/libs/binder/Parcel.cpp
sp<IBinder> Parcel::readStrongBinder() const
{sp<IBinder> val;// Note that a lot of code in Android reads binders by hand with this// method, and that code has historically been ok with getting nullptr// back (while ignoring error codes).readNullableStrongBinder(&val);return val;
}
↓
status_t Parcel::readNullableStrongBinder(sp<IBinder>* val) const
{return unflatten_binder(ProcessState::self(), *this, val);
}
↓
status_t unflatten_binder(const sp<ProcessState>& proc,const Parcel& in, sp<IBinder>* out)
{const flat_binder_object* flat = in.readObject(false);if (flat) {switch (flat->type) {case BINDER_TYPE_BINDER:*out = reinterpret_cast<IBinder*>(flat->cookie);return finish_unflatten_binder(NULL, *flat, in);case BINDER_TYPE_HANDLE:/* (2.1.1) 根据handle创建BpBinder */*out = proc->getStrongProxyForHandle(flat->handle);return finish_unflatten_binder(static_cast<BpBinder*>(out->get()), *flat, in);}}return BAD_TYPE;
}
↓
然后就来到了创建manager代理对象同样的位置:
frameworks/native/libs/binder/ProcessState.cpp:
sp<IBinder> ProcessState::getStrongProxyForHandle(int32_t handle)
{sp<IBinder> result;AutoMutex _l(mLock);/* (2.1.1.1) 查询BpBinder对象缓存,相同handle是否已经创建 */handle_entry* e = lookupHandleLocked(handle);if (e != NULL) {// We need to create a new BpBinder if there isn't currently one, OR we// are unable to acquire a weak reference on this current one. See comment// in getWeakProxyForHandle() for more info about this.IBinder* b = e->binder;if (b == NULL || !e->refs->attemptIncWeak(this)) {if (handle == 0) {// Special case for context manager...// The context manager is the only object for which we create// a BpBinder proxy without already holding a reference.// Perform a dummy transaction to ensure the context manager// is registered before we create the first local reference// to it (which will occur when creating the BpBinder).// If a local reference is created for the BpBinder when the// context manager is not present, the driver will fail to// provide a reference to the context manager, but the// driver API does not return status.//// Note that this is not race-free if the context manager// dies while this code runs.//// TODO: add a driver API to wait for context manager, or// stop special casing handle 0 for context manager and add// a driver API to get a handle to the context manager with// proper reference counting.Parcel data;status_t status = IPCThreadState::self()->transact(0, IBinder::PING_TRANSACTION, data, NULL, 0);if (status == DEAD_OBJECT)return NULL;}/* (2.1.1.2) 给新handle新创建一个对应BpBinder对象 */b = new BpBinder(handle);e->binder = b;if (b) e->refs = b->getWeakRefs();result = b;} else {// This little bit of nastyness is to allow us to add a primary// reference to the remote proxy when this team doesn't have one// but another team is sending the handle to us.result.force_set(b);e->refs->decWeak(this);}}return result;
}
根据BpBinder对象,使用interface_cast()函数创建一个BpMediaPlayerService对象的过程如下:
interface_cast()扩展为:
inline sp<IMediaPlayerService> interface_cast(const sp<IBinder>& obj)
{return IMediaPlayerService::asInterface(obj);
}
IMediaPlayerService定义在:
frameworks/av/media/libmedia/IMediaPlayerService.cpp:
IMPLEMENT_META_INTERFACE(MediaPlayerService, "android.media.IMediaPlayerService");
展开为:
#define IMPLEMENT_META_INTERFACE(MediaPlayerService, "android.os.IServiceManager") \const ::android::String16 IMediaPlayerService::descriptor("android.os.IServiceManager"); \const ::android::String16& \IMediaPlayerService::getInterfaceDescriptor() const { \return IMediaPlayerService::descriptor; \} \::android::sp<IMediaPlayerService> IMediaPlayerService::asInterface( \const ::android::sp<::android::IBinder>& obj) \{ \::android::sp<IMediaPlayerService> intr; \if (obj != NULL) { \intr = static_cast<IMediaPlayerService*>( \obj->queryLocalInterface( \IMediaPlayerService::descriptor).get()); \if (intr == NULL) { \/* (3.1) 根据BpBinder对象,创建一个BpMediaPlayerService对象 */intr = new BpMediaPlayerService(obj); \} \} \return intr; \} \IMediaPlayerService::IMediaPlayerService() { } \IMediaPlayerService::~IMediaPlayerService() { } \
BpMediaPlayerService的定义为:
frameworks/av/media/libmedia/IMediaPlayerService.cpp:
class BpMediaPlayerService: public BpInterface<IMediaPlayerService>
{
public:explicit BpMediaPlayerService(const sp<IBinder>& impl): BpInterface<IMediaPlayerService>(impl){}virtual sp<IMediaMetadataRetriever> createMetadataRetriever(){Parcel data, reply;data.writeInterfaceToken(IMediaPlayerService::getInterfaceDescriptor());remote()->transact(CREATE_METADATA_RETRIEVER, data, &reply);return interface_cast<IMediaMetadataRetriever>(reply.readStrongBinder());}};
还是借用老罗的一张图总结service_client类之间复杂的关系:
4.5、service thread管理
binder service初始会启动2个main线程来提供服务,在等待service服务过多的情况下会动态的增加binder线程的数量,但是目前没有实现动态减少binder线程可能觉得cache着更好。
service一般默认最大考验开启15个线程,这个数值也可以通过ioctl的BINDER_SET_MAX_THREADS命令来修改。
动态增加binder线程的动作是binder驱动完成的,因为驱动可以看到service进程整个的阻塞情况。
具体驱动代码binder.c:
static int binder_thread_read(struct binder_proc *proc,struct binder_thread *thread,binder_uintptr_t binder_buffer, size_t size,binder_size_t *consumed, int non_block)
{if (proc->requested_threads == 0 &&list_empty(&thread->proc->waiting_threads) &&proc->requested_threads_started < proc->max_threads &&(thread->looper & (BINDER_LOOPER_STATE_REGISTERED |BINDER_LOOPER_STATE_ENTERED)) /* the user-space code fails to *//*spawn a new thread if we leave this out */) {proc->requested_threads++;binder_inner_proc_unlock(proc);binder_debug(BINDER_DEBUG_THREADS,"%d:%d BR_SPAWN_LOOPER\n",proc->pid, thread->pid);/* (1) 判断阻塞的情况下发送BR_SPAWN_LOOPER命令,通知native增加接收线程 */if (put_user(BR_SPAWN_LOOPER, (uint32_t __user *)buffer))return -EFAULT;binder_stat_br(proc, thread, BR_SPAWN_LOOPER);} }
frameworks/native/libs/binder/IPCThreadState.cpp:
status_t IPCThreadState::executeCommand(int32_t cmd)
{case BR_SPAWN_LOOPER:mProcess->spawnPooledThread(false);break;}
↓
frameworks/native/libs/binder/ProcessState.cpp:
void ProcessState::spawnPooledThread(bool isMain)
{if (mThreadPoolStarted) {String8 name = makeBinderThreadName();ALOGV("Spawning new pooled thread, name=%s\n", name.string());/* (1.1) 创建新的binder接收线程 */sp<Thread> t = new PoolThread(isMain);t->run(name.string());}
}
4.6、死亡通知(DeathRecipient)
可以使用BC_REQUEST_DEATH_NOTIFICATION注册死亡通知,在server端正常或者异常死亡的情况下都能收到通知。
在server端进程正常或者异常退出时,会关闭进程所有打开的文件句柄:
do_exit()
↓
exit_files()
↓
put_files_struct()
↓
static struct fdtable *close_files(struct files_struct * files)
{/** It is safe to dereference the fd table without RCU or* ->file_lock because this is the last reference to the* files structure.*/struct fdtable *fdt = rcu_dereference_raw(files->fdt);unsigned int i, j = 0;for (;;) {unsigned long set;i = j * BITS_PER_LONG;if (i >= fdt->max_fds)break;set = fdt->open_fds[j++];while (set) {if (set & 1) {struct file * file = xchg(&fdt->fd[i], NULL);if (file) {filp_close(file, files);cond_resched_rcu_qs();}}i++;set >>= 1;}}return fdt;
}
最终会调用到binder fd的release函数,调用到死亡通知的回调:
static int binder_release(struct inode *nodp, struct file *filp)
{struct binder_proc *proc = filp->private_data;debugfs_remove(proc->debugfs_entry);binder_defer_work(proc, BINDER_DEFERRED_RELEASE);return 0;
}
↓
static void
binder_defer_work(struct binder_proc *proc, enum binder_deferred_state defer)
{mutex_lock(&binder_deferred_lock);proc->deferred_work |= defer;if (hlist_unhashed(&proc->deferred_work_node)) {hlist_add_head(&proc->deferred_work_node,&binder_deferred_list);schedule_work(&binder_deferred_work);}mutex_unlock(&binder_deferred_lock);
}
5、java实现
略
6、AIDL(Android Interface Definition Language)
略
参考资料:
1、Android系统进程间通信(IPC)机制 罗升阳
2、Android Binder 分析
3、Android Bander设计与实现
4、Binder实现原理分析
5、一篇文章了解相见恨晚的 Android Binder 进程间通讯机制
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