一 Zygote fork
Zygote fork SystemServer 的过程如下：
ZygoteInit#forkSystemServer
ZygoteInit#handleSystemServerProcess
ZygoteInit#zygoteInit
RuntimeInit#applicationInit
RuntimeInit#findStaticMain
1.1 Zygote fork SystemServer 进程
ZygoteInit#forkSystemServer 配置system_server 的参数，uid gid 进程显示的名字等，然后调用native 的fork, 在子进程中调用handleSystemServerProcess
ZygoteInit.java
ZygoteServer zygoteServer) {
/* Hardcoded command line to start the system server */
String args[] = { "--setuid=1000", "--setgid=1000", "--setgroups=1001,1002,1003,1004,1005,1006,1007,1008,1009,1010,1018,1021,1023,1024,1032,1065,3001,3002,3003,3006,3007,3009,3010", "--capabilities=" + capabilities + "," + capabilities, "--nice-name=system_server", "--runtime-args", "--target-sdk-version=" + VMRuntime.SDK_VERSION_CUR_DEVELOPMENT, "com.android.server.SystemServer",
}; try { /* Request to fork the system server process */
pid = Zygote.forkSystemServer(
parsedArgs.uid, parsedArgs.gid,
parsedArgs.gids,
parsedArgs.runtimeFlags, null,
parsedArgs.permittedCapabilities,
parsedArgs.effectiveCapabilities);
} catch (IllegalArgumentException ex) { throw new RuntimeException(ex);
} /* For child process */
if (pid == 0) { if (hasSecondZygote(abiList)) {
waitForSecondaryZygote(socketName);
}
zygoteServer.closeServerSocket(); return handleSystemServerProcess(parsedArgs);
} return null;
}
1.2 System_service 进程启动，准备加载的ClassLoader
ZygoteInit.java private static Runnable handleSystemServerProcess(ZygoteConnection.Arguments parsedArgs) { // set umask to 0077 so new files and directories will default to owner-only permissions.
if (parsedArgs.invokeWith != null) {
} else {
ClassLoader cl = null; if (systemServerClasspath != null) {
cl = createPathClassLoader(systemServerClasspath, parsedArgs.targetSdkVersion);
Thread.currentThread().setContextClassLoader(cl);
} /*
* Pass the remaining arguments to SystemServer.
*/
return ZygoteInit.zygoteInit(parsedArgs.targetSdkVersion, parsedArgs.remainingArgs, cl);
} /* should never reach here */
}
1.3 RuntimeInit 初始化，进一步的准备初始化的环境
ZygoteInit.java public static final Runnable zygoteInit(int targetSdkVersion, String[] argv, ClassLoader classLoader) {
RuntimeInit.commonInit();
ZygoteInit.nativeZygoteInit(); return RuntimeInit.applicationInit(targetSdkVersion, argv, classLoader);
}
1.4 通过findStaticMain 方法反射调用System_Server 的main 方法。
RuntimeInit.java protected static Runnable applicationInit(int targetSdkVersion, String[] argv,
ClassLoader classLoader) {
// Remaining arguments are passed to the start class's static main
return findStaticMain(args.startClass, args.startArgs, classLoader);
}
二 SystemServer进程
2.1 SystemServer 启动，然后运行 run 方法。
SystemServer.java public static void main(String[] args) { new SystemServer().run();
} public SystemServer() { // Check for factory test mode.
mFactoryTestMode = FactoryTest.getMode(); // Remember if it's runtime restart(when sys.boot_completed is already set) or reboot
mRuntimeRestart = "1".equals(SystemProperties.get("sys.boot_completed"));
mRuntimeStartElapsedTime = SystemClock.elapsedRealtime();
mRuntimeStartUptime = SystemClock.uptimeMillis();
}
2.2 System_Server 的run 方法
开始首先配置 VM 参数
Binder 参数，
Loop.prepareMainLooper,
创建系统Context createSystemContext
启动系统的各种服务，包括AMS。startBootstrapServices() startCoreServices() startOtherServices()
Looper.Loop();
private void run() { try {
......
// the property. http://b/11463182
SystemProperties.set("persist.sys.dalvik.vm.lib.2", VMRuntime.getRuntime().vmLibrary()); // Mmmmmm... more memory!
VMRuntime.getRuntime().clearGrowthLimit(); // The system server has to run all of the time, so it needs to be
// as efficient as possible with its memory usage.
VMRuntime.getRuntime().setTargetHeapUtilization(0.8f);
......
// Ensure binder calls into the system always run at foreground priority.
BinderInternal.disableBackgroundScheduling(true); // Increase the number of binder threads in system_server
BinderInternal.setMaxThreads(sMaxBinderThreads); // Prepare the main looper thread (this thread).
android.os.Process.setThreadPriority(
android.os.Process.THREAD_PRIORITY_FOREGROUND);
android.os.Process.setCanSelfBackground(false);
Looper.prepareMainLooper();
Looper.getMainLooper().setSlowLogThresholdMs(
SLOW_DISPATCH_THRESHOLD_MS, SLOW_DELIVERY_THRESHOLD_MS); // Initialize native services.
System.loadLibrary("android_servers"); // Initialize the system context.
createSystemContext();
} finally {
} // Start services.
try {
traceBeginAndSlog("StartServices");
startBootstrapServices();
startCoreServices();
startOtherServices();
SystemServerInitThreadPool.shutdown();
} catch (Throwable ex) {
} finally {
traceEnd();
}
StrictMode.initVmDefaults(null);
// Loop forever.
Looper.loop(); throw new RuntimeException("Main thread loop unexpectedly exited");
}
三 AMS 运行
SystemServer#startBootstrapServices 通过mSystemServiceManager 启动ActivityManagerService。
启动ActivityManagerService
3.1 mSystemServiceManager.startService
private void startBootstrapServices() {
// Activity manager runs the show.
mActivityManagerService = mSystemServiceManager.startService(
ActivityManagerService.Lifecycle.class).getService();
mActivityManagerService.setSystemServiceManager(mSystemServiceManager);
mActivityManagerService.setSystemProcess();
3.2 启动ActivityManagerService
ActivityManagerService 准备工作线程，
准备Android 四大组件相关的数据结构，
public ActivityManagerService(Context systemContext)
mContext = systemCotex
mSystemThread = ActivityThread.currentActivityThread();
mUiContext = mSystemThread.getSystemUiContext();
mHandlerThread = new ServiceThread(TAG,
THREAD_PRIORITY_FOREGROUND, false /*allowIo*/);
mHandlerThread.start();
mHandler = new MainHandler(mHandlerThread.getLooper());
mUiHandler = mInjector.getUiHandler(this);
mFgBroadcastQueue = new BroadcastQueue(this, mHandler, "foreground", BROADCAST_FG_TIMEOUT, false);
mBgBroadcastQueue = new BroadcastQueue(this, mHandle "background", BROADCAST_BG_TIMEOUT, true);
mBroadcastQueues[0] = mFgBroadcastQueue;
mBroadcastQueues[1] = mBgBroadcastQueue;
mServices = new ActiveServices(this);
mProviderMap = new ProviderMap(this);
mStackSupervisor = createStackSupervisor();
mActivityStarter = new ActivityStarter(this, mStackSupervisor);
mRecentTasks = new RecentTasks(this, mStackSupervisor);
}
3.3 AMS setSystemProcess()
AMS 通过 setSystemProcess 把System_Server 进程加入到AMS 的进程管理中。加载 framework-res.apk
public void setSystemProcess() { try {
ServiceManager.addService(Context.ACTIVITY_SERVICE, this, /* allowIsolated= */ true,
DUMP_FLAG_PRIORITY_CRITICAL | DUMP_FLAG_PRIORITY_NORMAL | DUMP_FLAG_PROTO);
ServiceManager.addService(ProcessStats.SERVICE_NAME, mProcessStats);
ServiceManager.addService("meminfo", new MemBinder(this), /* allowIsolated= */ false,
DUMP_FLAG_PRIORITY_HIGH);
ServiceManager.addService("gfxinfo", new GraphicsBinder(this));
ServiceManager.addService("dbinfo", new DbBinder(this));
ServiceManager.addService("permission", new PermissionController(this));
ServiceManager.addService("processinfo", new ProcessInfoService(this));
ApplicationInfo info = mContext.getPackageManager().getApplicationInfo( "android", STOCK_PM_FLAGS | MATCH_SYSTEM_ONLY);
mSystemThread.installSystemApplicationInfo(info, getClass().getClassLoader()); synchronized (this) {
ProcessRecord app = newProcessRecordLocked(info, info.processName, false, 0);
app.persistent = true;
app.pid = MY_PID;
app.maxAdj = ProcessList.SYSTEM_ADJ;
app.makeActive(mSystemThread.getApplicationThread(), mProcessStats); synchronized (mPidsSelfLocked) {
mPidsSelfLocked.put(app.pid, app);
}
updateLruProcessLocked(app, false, null);
updateOomAdjLocked();
}
} catch (PackageManager.NameNotFoundException e) { throw new RuntimeException( "Unable to find android system package", e);
}
}
3.4 installSystemProviders
在中startOtherServices 安装 SettingProvider
mActivityManagerService.installSystemProviders();
3.5 setWindowManager
mActivityManagerService.setWindowManager(wm);
3.6 systemReady
各种服务启动完毕后，systemReady. 在systemReady 中先启动SystemUI, 然后启动Launcher.