/frameworks/base/cmds/app_process/App_main.cpp （内含AppRuntime类）
/frameworks/base/core/jni/AndroidRuntime.cpp
/frameworks/base/core/java/com/android/internal/os/ZygoteInit.java
/frameworks/base/core/java/com/android/internal/os/Zygote.java
/frameworks/base/core/java/android/net/LocalServerSocket.java

App_main.mainAndroidRuntime.startstartVmstartRegZygoteInit.mainregisterZygoteSocketpreloadstartSystemServerrunSelectLoop

int main(int argc, char* const argv[])
{AppRuntime runtime(argv[0], computeArgBlockSize(argc, argv));//忽略第一个参数argc--;argv++;int i;for (i = 0; i < argc; i++) {if (argv[i][0] != '-') {break;}if (argv[i][1] == '-' && argv[i][2] == 0) {++i;break;}runtime.addOption(strdup(argv[i]));}//参数解析bool zygote = false;bool startSystemServer = false;bool application = false;String8 niceName;String8 className;++i;while (i < argc) {const char* arg = argv[i++];if (strcmp(arg, "--zygote") == 0) {zygote = true;niceName = ZYGOTE_NICE_NAME; //对于64位系统nice_name为zygote64,32位系统为zygote} else if (strcmp(arg, "--start-system-server") == 0) {startSystemServer = true;} else if (strcmp(arg, "--application") == 0) {application = true;} else if (strncmp(arg, "--nice-name=", 12) == 0) {niceName.setTo(arg + 12);} else if (strncmp(arg, "--", 2) != 0) {className.setTo(arg);break;} else {--i;break;}}Vector<String8> args;if (!className.isEmpty()) {// 运行application或tool程序args.add(application ? String8("application") : String8("tool"));runtime.setClassNameAndArgs(className, argc - i, argv + i);} else {//进入zygote模式，创建 /data/dalvik-cache路径maybeCreateDalvikCache();if (startSystemServer) {args.add(String8("start-system-server"));}char prop[PROP_VALUE_MAX];if (property_get(ABI_LIST_PROPERTY, prop, NULL) == 0) {return 11;}String8 abiFlag("--abi-list=");abiFlag.append(prop);args.add(abiFlag);for (; i < argc; ++i) {args.add(String8(argv[i]));}}//设置进程名if (!niceName.isEmpty()) {runtime.setArgv0(niceName.string());set_process_name(niceName.string());}if (zygote) {// 启动AppRuntime 【见小节3】runtime.start("com.android.internal.os.ZygoteInit", args, zygote);} else if (className) {runtime.start("com.android.internal.os.RuntimeInit", args, zygote);} else {//没有指定类名或zygote，参数错误return 10;}
}

 app_process [可选参数] 命令所在路径 启动的类名 [可选参数]

void AndroidRuntime::start(const char* className, const Vector<String8>& options, bool zygote)
{static const String8 startSystemServer("start-system-server");for (size_t i = 0; i < options.size(); ++i) {if (options[i] == startSystemServer) {const int LOG_BOOT_PROGRESS_START = 3000;}}const char* rootDir = getenv("ANDROID_ROOT");if (rootDir == NULL) {rootDir = "/system";if (!hasDir("/system")) {return;}setenv("ANDROID_ROOT", rootDir, 1);}JniInvocation jni_invocation;jni_invocation.Init(NULL);JNIEnv* env;// 虚拟机创建【见小节3.1】if (startVm(&mJavaVM, &env, zygote) != 0) {return;}onVmCreated(env);// JNI方法注册【见小节3.2】if (startReg(env) < 0) {ALOGE("Unable to register all android natives\n");return;}jclass stringClass;jobjectArray strArray;jstring classNameStr;//等价 strArray= new String[options.size() + 1];stringClass = env->FindClass("java/lang/String");strArray = env->NewObjectArray(options.size() + 1, stringClass, NULL);//等价 strArray[0] = "com.android.internal.os.ZygoteInit"classNameStr = env->NewStringUTF(className);env->SetObjectArrayElement(strArray, 0, classNameStr);//等价 strArray[1] = "start-system-server"；//   strArray[2] = "--abi-list=xxx"；其中xxx为系统响应的cpu架构类型，比如arm64-v8a.for (size_t i = 0; i < options.size(); ++i) {jstring optionsStr = env->NewStringUTF(options.itemAt(i).string());env->SetObjectArrayElement(strArray, i + 1, optionsStr);}//将"com.android.internal.os.ZygoteInit"转换为"com/android/internal/os/ZygoteInit"char* slashClassName = toSlashClassName(className);jclass startClass = env->FindClass(slashClassName);if (startClass == NULL) {ALOGE("JavaVM unable to locate class '%s'\n", slashClassName);} else {jmethodID startMeth = env->GetStaticMethodID(startClass, "main","([Ljava/lang/String;)V");if (startMeth == NULL) {ALOGE("JavaVM unable to find main() in '%s'\n", className);} else {// 调用ZygoteInit.main()方法【见小节4.0】env->CallStaticVoidMethod(startClass, startMeth, strArray);}}free(slashClassName); //释放相应对象的内存空间if (mJavaVM->DetachCurrentThread() != JNI_OK)ALOGW("Warning: unable to detach main thread\n");if (mJavaVM->DestroyJavaVM() != 0)ALOGW("Warning: VM did not shut down cleanly\n");
}

int AndroidRuntime::startVm(JavaVM** pJavaVM, JNIEnv** pEnv, bool zygote)
{// JNI检测功能，用于native层调用jni函数时进行常规检测，比较弱字符串格式是否符合要求，资源是否正确释放。该功能一般用于早期系统调试或手机Eng版，对于User版往往不会开启，引用该功能比较消耗系统CPU资源，降低系统性能。bool checkJni = false;property_get("dalvik.vm.checkjni", propBuf, "");if (strcmp(propBuf, "true") == 0) {checkJni = true;} else if (strcmp(propBuf, "false") != 0) {property_get("ro.kernel.android.checkjni", propBuf, "");if (propBuf[0] == '1') {checkJni = true;}}if (checkJni) {addOption("-Xcheck:jni");}//虚拟机产生的trace文件，主要用于分析系统问题，路径默认为/data/anr/traces.txtparseRuntimeOption("dalvik.vm.stack-trace-file", stackTraceFileBuf, "-Xstacktracefile:");//对于不同的软硬件环境，这些参数往往需要调整、优化，从而使系统达到最佳性能parseRuntimeOption("dalvik.vm.heapstartsize", heapstartsizeOptsBuf, "-Xms", "4m");parseRuntimeOption("dalvik.vm.heapsize", heapsizeOptsBuf, "-Xmx", "16m");parseRuntimeOption("dalvik.vm.heapgrowthlimit", heapgrowthlimitOptsBuf, "-XX:HeapGrowthLimit=");parseRuntimeOption("dalvik.vm.heapminfree", heapminfreeOptsBuf, "-XX:HeapMinFree=");parseRuntimeOption("dalvik.vm.heapmaxfree", heapmaxfreeOptsBuf, "-XX:HeapMaxFree=");parseRuntimeOption("dalvik.vm.heaptargetutilization",heaptargetutilizationOptsBuf, "-XX:HeapTargetUtilization=");//preloaded-classes文件内容是由WritePreloadedClassFile.java生成的，在ZygoteInit类中会预加载工作将其中的classes提前加载到内存，以提高系统性能if (!hasFile("/system/etc/preloaded-classes")) {return -1;}//创建虚拟机if (JNI_CreateJavaVM(pJavaVM, pEnv, &initArgs) < 0) {ALOGE("JNI_CreateJavaVM failed\n");return -1;}
}

int AndroidRuntime::startReg(JNIEnv* env)
{//设置线程创建方法为javaCreateThreadEtcandroidSetCreateThreadFunc((android_create_thread_fn) javaCreateThreadEtc);env->PushLocalFrame(200);//进程NI方法的注册if (register_jni_procs(gRegJNI, NELEM(gRegJNI), env) < 0) {env->PopLocalFrame(NULL);return -1;}env->PopLocalFrame(NULL);return 0;
}

static int register_jni_procs(const RegJNIRec array[], size_t count, JNIEnv* env)
{for (size_t i = 0; i < count; i++) {if (array[i].mProc(env) < 0) { 【见下文】return -1;}}return 0;
}

static const RegJNIRec gRegJNI[] = {REG_JNI(register_com_android_internal_os_RuntimeInit),REG_JNI(register_android_os_Binder)，...
}；

#define REG_JNI(name)      { name }
struct RegJNIRec {int (*mProc)(JNIEnv*);
};

int register_com_android_internal_os_RuntimeInit(JNIEnv* env)
{return jniRegisterNativeMethods(env, "com/android/internal/os/RuntimeInit",gMethods, NELEM(gMethods));
}//gMethods：java层方法名与jni层的方法的一一映射关系
static JNINativeMethod gMethods[] = {{ "nativeFinishInit", "()V",(void*) com_android_internal_os_RuntimeInit_nativeFinishInit },{ "nativeZygoteInit", "()V",(void*) com_android_internal_os_RuntimeInit_nativeZygoteInit },{ "nativeSetExitWithoutCleanup", "(Z)V",(void*) com_android_internal_os_RuntimeInit_nativeSetExitWithoutCleanup },
};

public static void main(String argv[]) {try {RuntimeInit.enableDdms(); //开启DDMS功能SamplingProfilerIntegration.start();boolean startSystemServer = false;String socketName = "zygote";String abiList = null;for (int i = 1; i < argv.length; i++) {if ("start-system-server".equals(argv[i])) {startSystemServer = true;} else if (argv[i].startsWith(ABI_LIST_ARG)) {abiList = argv[i].substring(ABI_LIST_ARG.length());} else if (argv[i].startsWith(SOCKET_NAME_ARG)) {socketName = argv[i].substring(SOCKET_NAME_ARG.length());} else {throw new RuntimeException("Unknown command line argument: " + argv[i]);}}if (abiList == null) {throw new RuntimeException("No ABI list supplied.");}registerZygoteSocket(socketName); //为Zygote注册socket【见小节4.1】preload(); // 预加载类和资源【见小节4.2】SamplingProfilerIntegration.writeZygoteSnapshot();gcAndFinalize(); //GC操作if (startSystemServer) {startSystemServer(abiList, socketName);//启动system_server【见小节4.3】}runSelectLoop(abiList); //进入循环模式【见小节4.4】closeServerSocket();} catch (MethodAndArgsCaller caller) {caller.run(); //启动system_server中会讲到。} catch (RuntimeException ex) {closeServerSocket();throw ex;}
}

private static void registerZygoteSocket(String socketName) {if (sServerSocket == null) {int fileDesc;final String fullSocketName = ANDROID_SOCKET_PREFIX + socketName;try {String env = System.getenv(fullSocketName);fileDesc = Integer.parseInt(env);} catch (RuntimeException ex) {throw new RuntimeException(fullSocketName + " unset or invalid", ex);}try {FileDescriptor fd = new FileDescriptor();fd.setInt$(fileDesc); //设置文件描述符sServerSocket = new LocalServerSocket(fd); //创建Socket的本地服务端} catch (IOException ex) {throw new RuntimeException("Error binding to local socket '" + fileDesc + "'", ex);}}
}

static void preload() {//预加载位于/system/etc/preloaded-classes文件中的类preloadClasses(); //预加载资源，包含drawable和color资源preloadResources();//预加载OpenGLpreloadOpenGL();//通过System.loadLibrary()方法，//预加载"android","compiler_rt","jnigraphics"这3个共享库preloadSharedLibraries();//预加载  文本连接符资源preloadTextResources();//仅用于zygote进程，用于内存共享的进程WebViewFactory.prepareWebViewInZygote();
}

private static boolean startSystemServer(String abiList, String socketName)throws MethodAndArgsCaller, RuntimeException {long capabilities = posixCapabilitiesAsBits(OsConstants.CAP_BLOCK_SUSPEND,OsConstants.CAP_KILL,OsConstants.CAP_NET_ADMIN,OsConstants.CAP_NET_BIND_SERVICE,OsConstants.CAP_NET_BROADCAST,OsConstants.CAP_NET_RAW,OsConstants.CAP_SYS_MODULE,OsConstants.CAP_SYS_NICE,OsConstants.CAP_SYS_RESOURCE,OsConstants.CAP_SYS_TIME,OsConstants.CAP_SYS_TTY_CONFIG);//参数准备String args[] = {"--setuid=1000","--setgid=1000","--setgroups=1001,1002,1003,1004,1005,1006,1007,1008,1009,1010,1018,1021,1032,3001,3002,3003,3006,3007","--capabilities=" + capabilities + "," + capabilities,"--nice-name=system_server","--runtime-args","com.android.server.SystemServer",};ZygoteConnection.Arguments parsedArgs = null;int pid;try {//用于解析参数，生成目标格式parsedArgs = new ZygoteConnection.Arguments(args);ZygoteConnection.applyDebuggerSystemProperty(parsedArgs);ZygoteConnection.applyInvokeWithSystemProperty(parsedArgs);// fork子进程，用于运行system_serverpid = Zygote.forkSystemServer(parsedArgs.uid, parsedArgs.gid,parsedArgs.gids,parsedArgs.debugFlags,null,parsedArgs.permittedCapabilities,parsedArgs.effectiveCapabilities);} catch (IllegalArgumentException ex) {throw new RuntimeException(ex);}//进入子进程system_serverif (pid == 0) {if (hasSecondZygote(abiList)) {waitForSecondaryZygote(socketName);}// 完成system_server进程剩余的工作handleSystemServerProcess(parsedArgs);}return true;
}

private static void runSelectLoop(String abiList) throws MethodAndArgsCaller {ArrayList<FileDescriptor> fds = new ArrayList<FileDescriptor>();ArrayList<ZygoteConnection> peers = new ArrayList<ZygoteConnection>();//sServerSocket是socket通信中的服务端，即zygote进程fds.add(sServerSocket.getFileDescriptor());peers.add(null);while (true) {StructPollfd[] pollFds = new StructPollfd[fds.size()];for (int i = 0; i < pollFds.length; ++i) {pollFds[i] = new StructPollfd();pollFds[i].fd = fds.get(i);pollFds[i].events = (short) POLLIN;}try {Os.poll(pollFds, -1);} catch (ErrnoException ex) {throw new RuntimeException("poll failed", ex);}for (int i = pollFds.length - 1; i >= 0; --i) {//采用I/O多路复用机制，当客户端发出连接请求或者数据处理请求时，跳过continue，执行后面的代码if ((pollFds[i].revents & POLLIN) == 0) {continue;}if (i == 0) {//创建客户端连接ZygoteConnection newPeer = acceptCommandPeer(abiList);peers.add(newPeer);fds.add(newPeer.getFileDesciptor());} else {//处理客户端数据事务boolean done = peers.get(i).runOnce();if (done) {peers.remove(i);fds.remove(i);}}}}
}