frameworks\base\core\java\com\android\internal\os\ZygoteInit.java的forkSystemServer
/* Request to fork the system server process */ pid = Zygote.forkSystemServer( parsedArgs.mUid, parsedArgs.mGid, parsedArgs.mGids, parsedArgs.mRuntimeFlags, null, parsedArgs.mPermittedCapabilities, parsedArgs.mEffectiveCapabilities); } catch (IllegalArgumentException ex) { throw new RuntimeException(ex); } /* For child process */ if (pid == 0) { if (hasSecondZygote(abiList)) { waitForSecondaryZygote(socketName); } zygoteServer.closeServerSocket(); return handleSystemServerProcess(parsedArgs); }
handleSystemServerProcess来启动SyetemServer进程。
handleSystemServerProcess关键代码
/* * Pass the remaining arguments to SystemServer. */ return ZygoteInit.zygoteInit(parsedArgs.mTargetSdkVersion, parsedArgs.mDisabledCompatChanges, parsedArgs.mRemainingArgs, cl);
public static final Runnable zygoteInit(int targetSdkVersion, long[] disabledCompatChanges, String[] argv, ClassLoader classLoader) { if (RuntimeInit.DEBUG) { Slog.d(RuntimeInit.TAG, "RuntimeInit: Starting application from zygote"); } Trace.traceBegin(Trace.TRACE_TAG_ACTIVITY_MANAGER, "ZygoteInit"); RuntimeInit.redirectLogStreams(); RuntimeInit.commonInit(); ZygoteInit.nativeZygoteInit(); return RuntimeInit.applicationInit(targetSdkVersion, disabledCompatChanges, argv, classLoader); }
nativeZygoteInit方法在 frameworks/base/core/jni/AndroidRuntime.cpp中定义
int register_com_android_internal_os_ZygoteInit_nativeZygoteInit(JNIEnv* env) { const JNINativeMethod methods[] = { { "nativeZygoteInit", "()V", (void*) com_android_internal_os_ZygoteInit_nativeZygoteInit }, }; return jniRegisterNativeMethods(env, "com/android/internal/os/ZygoteInit", methods, NELEM(methods)); }
对应的方法为com_android_internal_os_ZygoteInit_nativeZygoteInit
static void com_android_internal_os_ZygoteInit_nativeZygoteInit(JNIEnv* env, jobject clazz) { gCurRuntime->onZygoteInit(); }
这里gCurRuntime是AndroidRuntime类型的指针，AndroidRuntime的子类AppRuntime在app_main.cpp中定义，我们来查看AppRuntime的onZygoteInit函数，代码如下所示。
frameworks\base\cmds\app_process\app_main.cpp
virtual void onZygoteInit() { sp<ProcessState> proc = ProcessState::self(); ALOGV("App process: starting thread pool.\n"); //启动一个Binder线程池，这样SyetemServer进程就可以使用Binder来与其他进程进行通信了 proc->startThreadPool(); }
applicationInit在frameworks\base\core\java\com\android\internal\os\RuntimeInit.java中
protected static Runnable applicationInit(int targetSdkVersion, long[] disabledCompatChanges, String[] argv, ClassLoader classLoader) { // If the application calls System.exit(), terminate the process // immediately without running any shutdown hooks. It is not possible to // shutdown an Android application gracefully. Among other things, the // Android runtime shutdown hooks close the Binder driver, which can cause // leftover running threads to crash before the process actually exits. nativeSetExitWithoutCleanup(true); VMRuntime.getRuntime().setTargetSdkVersion(targetSdkVersion); VMRuntime.getRuntime().setDisabledCompatChanges(disabledCompatChanges); final Arguments args = new Arguments(argv); // The end of of the RuntimeInit event (see #zygoteInit). Trace.traceEnd(Trace.TRACE_TAG_ACTIVITY_MANAGER); // Remaining arguments are passed to the start class's static main return findStaticMain(args.startClass, args.startArgs, classLoader); }
findStaticMain方法主要调用了MethodAndArgsCaller(m, argv);
protected static Runnable findStaticMain(String className, String[] argv, ClassLoader classLoader) { Class<?> cl; try { cl = Class.forName(className, true, classLoader); } catch (ClassNotFoundException ex) { throw new RuntimeException( "Missing class when invoking static main " + className, ex); } Method m; try { m = cl.getMethod("main", new Class[] { String[].class }); } catch (NoSuchMethodException ex) { throw new RuntimeException( "Missing static main on " + className, ex); } catch (SecurityException ex) { throw new RuntimeException( "Problem getting static main on " + className, ex); } int modifiers = m.getModifiers(); if (! (Modifier.isStatic(modifiers) && Modifier.isPublic(modifiers))) { throw new RuntimeException( "Main method is not public and static on " + className); } /* * This throw gets caught in ZygoteInit.main(), which responds * by invoking the exception's run() method. This arrangement * clears up all the stack frames that were required in setting * up the process. */ return new MethodAndArgsCaller(m, argv); }
MethodAndArgsCaller的run方法调用
mMethod.invoke(null, new Object[] { mArgs });
SystemServer的main函数被动态调用。
进入SystemServer
frameworks\base\services\java\com\android\server\SystemServer.java
public static void main(String[] args) { new SystemServer().run(); }
run方法关键代码如下
System.loadLibrary("android_servers");加载了libandroid_servers.so // Create the system service manager. mSystemServiceManager = new SystemServiceManager(mSystemContext);创建SystemServiceManager，它会对系统的服务进行创建、启动和生命周期管理 startBootstrapServices(t); startCoreServices(t); startOtherServices(t);
| BootstrapServices | 作用 |
| Installer | 系统安装apk时的一个服务类，启动完成Installer服务之后才能启动其他的系统服务 |
| ActivityManagerService | 负责四大组件的启动、切换、调度。 |
| PowerManagerService | 计算系统中和Power相关的计算，然后决策系统应该如何反应 |
| LightsService | 管理和显示背光LED |
| DisplayManagerService | 用来管理所有显示设备 |
| UserManagerService | 多用户模式管理 |
| SensorService | 为系统提供各种感应器服务 |
| PackageManagerService | 用来对apk进行安装、解析、删除、卸载等等操作 |
| CoreServices | |
| BatteryService | 管理电池相关的服务 |
| UsageStatsService | 收集用户使用每一个APP的频率、使用时常 |
| WebViewUpdateService | WebView更新服务 |
| OtherServices | |
| CameraService | 摄像头相关服务 |
| AlarmManagerService | 全局定时器管理服务 |
| InputManagerService | 管理输入事件 |
| WindowManagerService | 窗口管理服务 |
| VrManagerService | VR模式管理服务 |
| BluetoothService | 蓝牙管理服务 |
| NotificationManagerService | 通知管理服务 |
| DeviceStorageMonitorService | 存储相关管理服务 |
| LocationManagerService | 定位管理服务 |
| AudioService | 音频相关管理服务 |
| … | …. |
显示详细信息
要启动那个服务，调用SystemServiceManager的startService方法即可
mPowerManagerService = mSystemServiceManager.startService(PowerManagerService.class);
frameworks\base\services\core\java\com\android\server\SystemServiceManager.java
public SystemService startService(String className) { final Class<SystemService> serviceClass = loadClassFromLoader(className, this.getClass().getClassLoader()); return startService(serviceClass); }
public <T extends SystemService> T startService(Class<T> serviceClass) { try { final String name = serviceClass.getName(); Slog.i(TAG, "Starting " + name); Trace.traceBegin(Trace.TRACE_TAG_SYSTEM_SERVER, "StartService " + name); // Create the service. if (!SystemService.class.isAssignableFrom(serviceClass)) { throw new RuntimeException("Failed to create " + name + ": service must extend " + SystemService.class.getName()); } final T service; try { Constructor<T> constructor = serviceClass.getConstructor(Context.class); service = constructor.newInstance(mContext);创建service实例 } catch (InstantiationException ex) { throw new RuntimeException("Failed to create service " + name + ": service could not be instantiated", ex); } catch (IllegalAccessException ex) { throw new RuntimeException("Failed to create service " + name + ": service must have a public constructor with a Context argument", ex); } catch (NoSuchMethodException ex) { throw new RuntimeException("Failed to create service " + name + ": service must have a public constructor with a Context argument", ex); } catch (InvocationTargetException ex) { throw new RuntimeException("Failed to create service " + name + ": service constructor threw an exception", ex); } startService(service); return service; } finally { Trace.traceEnd(Trace.TRACE_TAG_SYSTEM_SERVER); } } public void startService(@NonNull final SystemService service) { // Register it. mServices.add(service); // Start it. long time = SystemClock.elapsedRealtime(); try { 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"); }
总结SyetemServer进程
SyetemServer在启动时做了如下工作：
1.启动Binder线程池，这样就可以与其他进程进行通信。
2.创建SystemServiceManager用于对系统的服务进行创建、启动和生命周期管理。
3.启动各种系统服务。
