简介
源码使用官方 Android29
ActivityManagerService是Android提供的一个用于管理Activity运行状态的系统进程
启动过程
启动首先是从SystemService的main方法开始启动的
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/**
* The main entry point from zygote.
*/
public static void main(String[] args) {
new SystemServer().run();
}
从官方注射可以看到，这个是由zygote启动的服务
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private void run() {
TimingsTraceAndSlog t = new TimingsTraceAndSlog();
try {
// ...
// 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);
SystemServiceRegistry.sEnableServiceNotFoundWtf = true;
// Initialize native services.
System.loadLibrary("android_servers");
// Allow heap / perf profiling.
initZygoteChildHeapProfiling();
//...
// Create the system service manager.
mSystemServiceManager = new SystemServiceManager(mSystemContext);
mSystemServiceManager.setStartInfo(mRuntimeRestart, mRuntimeStartElapsedTime, mRuntimeStartUptime);
LocalServices.addService(SystemServiceManager.class, mSystemServiceManager);
} finally {
t.traceEnd(); // InitBeforeStartServices
}
// Setup the default WTF handler
RuntimeInit.setDefaultApplicationWtfHandler(SystemServer::handleEarlySystemWtf);
// Start services.
try {
t.traceBegin("StartServices");
// 启动很多Service
startBootstrapServices(t);
// 启动很多核心的系统服务
startCoreServices(t);
startOtherServices(t);
} catch (Throwable ex) {
Slog.e("System", "******************************************");
Slog.e("System", "************ Failure starting system services", ex);
throw ex;
} finally {
t.traceEnd(); // StartServices
}
StrictMode.initVmDefaults(null);
if (!mRuntimeRestart && !isFirstBootOrUpgrade()) {
final long uptimeMillis = SystemClock.elapsedRealtime();
FrameworkStatsLog.write(FrameworkStatsLog.BOOT_TIME_EVENT_ELAPSED_TIME_REPORTED,
FrameworkStatsLog.BOOT_TIME_EVENT_ELAPSED_TIME__EVENT__SYSTEM_SERVER_READY,
uptimeMillis);
final long maxUptimeMillis = 60 * 1000;
if (uptimeMillis > maxUptimeMillis) {
Slog.wtf(SYSTEM_SERVER_TIMING_TAG,
"SystemServer init took too long. uptimeMillis=" + uptimeMillis);
}
}
// Loop forever.
Looper.loop();
throw new RuntimeException("Main thread loop unexpectedly exited");
}
SystemService启动后也是利用的Handler进行循环处理，期间使用SystemServiceManager启动了很多系统服务，例如Activity栈管理、系统配置、电源管理等。
AMS触发Activity生命周期
AMS对Activity的生命周期分发主要通过ClientTransaction携带不同的生命周期方法，例如LaunchActivityItem、ResumeActivityItem、PauseActivityItem等来实现的。
Acitity栈
在AMS上使用ActivityDisplay、ActivityStack、TaskRecord、ActivityRecord等来管理不同进程以及屏幕显示的Activity
// TODO 编译调试不同情况下ASM的调用过程