zygote进程
zygote 服务器从app_process启动后，会启动一个虚拟机。虚拟机执行第一个Java类是ZygoteInit.java.
ZygoteInit的main方法
public static void main(String argv[]) {
ZygoteServer zygoteServer = new ZygoteServer();
// Zygote goes into its own process group.
try {
Os.setpgid(0, 0);
} catch (ErrnoException ex) {
throw new RuntimeException("Failed to setpgid(0,0)", ex);
}
final Runnable caller;
try {
...
//1 创建一个ServerSocket
zygoteServer.registerServerSocket(socketName);
// In some configurations, we avoid preloading resources and classes eagerly.
// In such cases, we will preload things prior to our first fork.
// 2 预加载类和资源
if (!enableLazyPreload) {
bootTimingsTraceLog.traceBegin("ZygotePreload");
EventLog.writeEvent(LOG_BOOT_PROGRESS_PRELOAD_START,
SystemClock.uptimeMillis());
preload(bootTimingsTraceLog);
EventLog.writeEvent(LOG_BOOT_PROGRESS_PRELOAD_END,
SystemClock.uptimeMillis());
bootTimingsTraceLog.traceEnd(); // ZygotePreload
} else {
Zygote.resetNicePriority();
}
...
if (startSystemServer) {
//3 创建SystemServer进程
Runnable r = forkSystemServer(abiList, socketName, zygoteServer);
// {@code r == null} in the parent (zygote) process, and {@code r != null} in the
// child (system_server) process.
if (r != null) {
r.run();
return;
}
}
Log.i(TAG, "Accepting command socket connections");
// The select loop returns early in the child process after a fork and
// loops forever in the zygote.
//如果是zygote进程，则运行该方法，一直阻塞。等待客户端消息，如果是其他进程则在上面return了。
//4
caller = zygoteServer.runSelectLoop(abiList);
} catch (Throwable ex) {
Log.e(TAG, "System zygote died with exception", ex);
throw ex;
} finally {
//5 关闭其他进程的socket端口
zygoteServer.closeServerSocket();
}
// We're in the child process and have exited the select loop. Proceed to execute the
// command.
if (caller != null) {
caller.run();
}
}
1 ZygoteInit main函数第一个重要工作就是启动一个Socket服务器端口
2 创建完Socket后，预装Framework大部分类及资源
3 加载完毕后，创建SystemServer进程
前面注释3的地方，创建新进程，此方法会返回两个结果，一个r为null。是当前进程，一个r不为null.是子进程。
当r为null时，则执行注释4。runSelectLoop方法里面是个死循环，等待客户端发送消息。
当r不为null时，则是在子进程，因为子进程不需要这个端口。因此关闭
private static Runnable forkSystemServer(String abiList, String socketName,
ZygoteServer zygoteServer) {
...
int pid;
try {
parsedArgs = new ZygoteConnection.Arguments(args);
ZygoteConnection.applyDebuggerSystemProperty(parsedArgs);
ZygoteConnection.applyInvokeWithSystemProperty(parsedArgs);
/* Request to fork the system server process */
//1 创建一个SystemServer进程
pid = Zygote.forkSystemServer(
parsedArgs.uid, parsedArgs.gid,
parsedArgs.gids,
parsedArgs.debugFlags,
null,
parsedArgs.permittedCapabilities,
parsedArgs.effectiveCapabilities);
} catch (IllegalArgumentException ex) {
throw new RuntimeException(ex);
}
/* For child process */
//2 SystemServer进程执行的代码
if (pid == 0) {
if (hasSecondZygote(abiList)) {
waitForSecondaryZygote(socketName);
}
//3 关闭socket的
zygoteServer.closeServerSocket();
return handleSystemServerProcess(parsedArgs);
}
return null;
}
注释 1 ，最终会调用nativeForkSystemServer方法创建一个进程
注释 2 pid == 0 则是创建出来的进程执行的代码。handleSystemServerProcess最终调用RuntimeInit里面的findStaticMain方法。该方的run方法里面执行目标的main方法
注释 3 关闭服务器端口。因为从zygote复制前一句创建了Socket服务端，这个服务端除了zygote自己，不应该被其他进程使用，否则系统中会有多个进程接收Socket客户端的命令
SystemServer进程
SystemServer是zygote孵化出的第一个进程，从ZygoteInit main函数调用startSystemServer()开始,最终调用nativeForkSystemServer方法
启动新进程后，关闭Socket服务器端。执行SystemServer的main方法
public static void main(String[] args) {
new SystemServer().run();
}
private void run() {
try {
...
// Prepare the main looper thread (this thread).
android.os.Process.setThreadPriority(
android.os.Process.THREAD_PRIORITY_FOREGROUND);
android.os.Process.setCanSelfBackground(false);
//设置Looper
Looper.prepareMainLooper();
// Initialize native services.
//加载so库
System.loadLibrary("android_servers");
// Check whether we failed to shut down last time we tried.
// This call may not return.
performPendingShutdown();
//创建一个ActivityThread,ContextImpl
// Initialize the system context.
createSystemContext();
// Create the system service manager.
mSystemServiceManager = new SystemServiceManager(mSystemContext);
mSystemServiceManager.setRuntimeRestarted(mRuntimeRestart);
LocalServices.addService(SystemServiceManager.class, mSystemServiceManager);
// Prepare the thread pool for init tasks that can be parallelized
//初始化一个包含执行任务的线程池的单例，某些服务在线程池中执行
SystemServerInitThreadPool.get();
} finally {
traceEnd(); // InitBeforeStartServices
}
// Start services.
try {
traceBeginAndSlog("StartServices");
//运行一些启动服务,比如电池管理服务，屏幕亮度服务，PMS服务
startBootstrapServices();
//运行一些核心服务,
startCoreServices();
//运行其他服务器
startOtherServices();
SystemServerInitThreadPool.shutdown();
} catch (Throwable ex) {
Slog.e("System", "******************************************");
Slog.e("System", "************ Failure starting system services", ex);
throw ex;
} finally {
traceEnd();
}
...
// Loop forever.
Looper.loop();
throw new RuntimeException("Main thread loop unexpectedly exited");
}
启动服务的大部分会调用到SystemServiceManager的startService方法
public void startService(@NonNull final SystemService service) {
// Register it.
mServices.add(service);
// Start it.
long time = SystemClock.elapsedRealtime();
try {
//调用 service 里面的onStart方法
service.onStart();
} catch (RuntimeException ex) {
throw new RuntimeException("Failed to start service " + service.getClass().getName()
+ ": onStart threw an exception", ex);
}
warnIfTooLong(SystemClock.elapsedRealtime() - time, service, "onStart");
}
也有些是直接运行mian方法，例如下，执行完后都会有如下ServiceManager.addService(xxx, m),把服务缓存起来。
mPackageManagerService = PackageManagerService.main(mSystemContext, installer,
mFactoryTestMode != FactoryTest.FACTORY_TEST_OFF, mOnlyCore);
public static PackageManagerService main(Context context, Installer installer,
boolean factoryTest, boolean onlyCore) {
// Self-check for initial settings.
PackageManagerServiceCompilerMapping.checkProperties();
PackageManagerService m = new PackageManagerService(context, installer,
factoryTest, onlyCore);
m.enableSystemUserPackages();
ServiceManager.addService("package", m);
final PackageManagerNative pmn = m.new PackageManagerNative();
ServiceManager.addService("package_native", pmn);
return m;
}
而ServiceManager.addService方法添加的是一个name对应一个IBinder引用。因为这些服务都是可以提供给其他进程使用的。所以理所当然就是IBinder
/**
* Place a new @a service called @a name into the service
* manager.
*
* @param name the name of the new service
* @param service the service object
*/
public static void addService(String name, IBinder service) {
try {
getIServiceManager().addService(name, service, false);
} catch (RemoteException e) {
Log.e(TAG, "error in addService", e);
}
}
在看PackageManagerService的构造方法，里面初始化了一个ServiceThread线程。其他的服务也都会有个线程
public PackageManagerService(Context context, Installer installer,
boolean factoryTest, boolean onlyCore) {
...
synchronized (mInstallLock) {
// writer
synchronized (mPackages) {
//生成一个线程。作为PackageManagerService当前的主线程
mHandlerThread = new ServiceThread(TAG,
Process.THREAD_PRIORITY_BACKGROUND, true /*allowIo*/);
mHandlerThread.start();
mHandler = new PackageHandler(mHandlerThread.getLooper());
}
在APK应用中能够直接交互的大部分系统服务都在systemServer进程中运行，比如WindowManagerServer,ActivityManagerSystemService,PackageManagerServer等常见服务，这些系统服务都是以一个线程的方式存在于SystemServer进程中。
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