深入理解AMS --- 一 AMS 的啟動

安卓開發 · 發表 2018-11-19 19:38:45

摘要：深入理解AMS --- 一 AMS 的啟動程式碼分支：android-9.0.0_r9 combo: aosp_x86_64-eng 一 Zygote fork Zygote fork SystemServer 的過程如下： ZygoteInit#forkSyst...

深入理解AMS --- 一 AMS 的啟動

程式碼分支：android-9.0.0_r9

combo: aosp_x86_64-eng

一 Zygote fork

Zygote fork SystemServer 的過程如下：

ZygoteInit#forkSystemServer
ZygoteInit#handleSystemServerProcess
ZygoteInit#zygoteInit
RuntimeInit#applicationInit
RuntimeInit#findStaticMain

1.1 Zygote fork SystemServer 程序

ZygoteInit#forkSystemServer 配置system_server 的引數，uid gid 程序顯示的名字等，然後呼叫native 的fork, 在子程序中呼叫handleSystemServerProcess

ZygoteInit.java

private static Runnable forkSystemServer(String abiList, String socketName,
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 程序啟動，準備載入的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，進一步的準備初始化的環境

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 通過findStaticMain 方法反射呼叫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程序

2.1 SystemServer 啟動，然後執行 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

開始首先配置 VM 引數
Binder 引數，
Loop.prepareMainLooper,
建立系統Context createSystemContext
啟動系統的各種服務，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 執行

SystemServer#startBootstrapServices 通過mSystemServiceManager 啟動ActivityManagerService。
啟動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 啟動ActivityManagerService

ActivityManagerService 準備工作執行緒，

準備Android 四大元件相關的資料結構，

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 通過 setSystemProcess 把System_Server 程序加入到AMS 的程序管理中。載入 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 安裝 SettingProvider

mActivityManagerService.installSystemProviders();

3.5 setWindowManager

mActivityManagerService.setWindowManager(wm);

3.6 systemReady

各種服務啟動完畢後，systemReady. 在systemReady 中先啟動SystemUI, 然後啟動Launcher.

5bdb1821e4b0e4521336b4f6.png

深入理解AMS --- 一 AMS 的啟動