前一篇文章讲到zygote启动SS进程，那么，SS会做些什么呢？
源码参考Android4.1.1，涉及文件有SystemServer.java等(framework文件夹下)
public static void main(String[] args) {
.....
.....
// Mmmmmm... more memory!
dalvik.system.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);
//system_init.cpp的代码将编译成libandroid_servers.so库
System.loadLibrary("android_servers");
init1(args);//调用到native层中的system_init.cpp中的system_init函数
}
init1是本地函数，通过JIN调用com_android_server_SystemServer_init1.cpp文件中的init1函数，然后这个函数有调用 system_init();（system_init.cpp）:
extern "C" status_t system_init()
{
ALOGI("Entered system_init()");
sp proc(ProcessState::self());
//获取到一个ServiceManager对象，SM是注册系统服务的关键人物
sp sm = defaultServiceManager();
ALOGI("ServiceManager: %p\n", sm.get());
sp grim = new GrimReaper();
sm->asBinder()->linkToDeath(grim, grim.get(), 0);
char propBuf[PROPERTY_VALUE_MAX];
property_get("system_init.startsurfaceflinger", propBuf, "1");
if (strcmp(propBuf, "1") == 0) {
// Start the SurfaceFlinger
SurfaceFlinger::instantiate();
}
property_get("system_init.startsensorservice", propBuf, "1");
if (strcmp(propBuf, "1") == 0) {
// Start the sensor service
SensorService::instantiate();
}
// And now start the Android runtime. We have to do this bit
// of nastiness because the Android runtime initialization requires
// some of the core system services to already be started.
// All other servers should just start the Android runtime at
// the beginning of their processes's main(), before calling
// the init function.
ALOGI("System server: starting Android runtime.\n");
AndroidRuntime* runtime = AndroidRuntime::getRuntime();
ALOGI("System server: starting Android services.\n");
JNIEnv* env = runtime->getJNIEnv();
if (env == NULL) {
return UNKNOWN_ERROR;
}
jclass clazz = env->FindClass("com/android/server/SystemServer");
if (clazz == NULL) {
return UNKNOWN_ERROR;
}
//下行获取成员函数id
jmethodID methodId = env->GetStaticMethodID(clazz, "init2", "()V");
if (methodId == NULL) {
return UNKNOWN_ERROR;
}
//下行将调用Java层的init2函数
env->CallStaticVoidMethod(clazz, methodId);
ALOGI("System server: entering thread pool.\n");
ProcessState::self()->startThreadPool();
IPCThreadState::self()->joinThreadPool();
ALOGI("System server: exiting thread pool.\n");
return NO_ERROR;
}
- 小结一下，这个本地函数的主要工作是做一些C++层的设置，然后call回Java层。
再看init2函数：
public static final void init2() {
Slog.i(TAG, "Entered the Android system server!");
Thread thr = new ServerThread();
thr.setName("android.server.ServerThread");
thr.start();//开启线程，创建
Java
层的各种服务
}
- 嗯，开启线程，等等，线程的工作内容是什么？
@Override
public void run() {
EventLog.writeEvent(EventLogTags.BOOT_PROGRESS_SYSTEM_RUN,
SystemClock.uptimeMillis());
Looper.prepare();
android.os.Process.setThreadPriority(
android.os.Process.THREAD_PRIORITY_FOREGROUND);
BinderInternal.disableBackgroundScheduling(true);
android.os.Process.setCanSelfBackground(false);
......
//包括（但不止）这些系统服务都会在此时被注册
//所以，加入你想写核心服务，你可能也需要在这里注册自己。
LightsService lights = null;
PowerManagerService power = null;
BatteryService battery = null;
VibratorService vibrator = null;
AlarmManagerService alarm = null;
NetworkManagementService networkManagement = null;
NetworkStatsService networkStats = null;
NetworkPolicyManagerService networkPolicy = null;
ConnectivityService connectivity = null;
WifiP2pService wifiP2p = null;
WifiService wifi = null;
NsdService serviceDiscovery= null;
IPackageManager pm = null;
Context context = null;
WindowManagerService wm = null;
BluetoothService bluetooth = null;
BluetoothA2dpService bluetoothA2dp = null;
DockObserver dock = null;
UsbService usb = null;
SerialService serial = null;
UiModeManagerService uiMode = null;
RecognitionManagerService recognition = null;
ThrottleService throttle = null;
NetworkTimeUpdateService networkTimeUpdater = null;
CommonTimeManagementService commonTimeMgmtService = null;
InputManagerService inputManager = null;
......
Slog.i(TAG, "Alarm Manager");
//new 出AlarmManagerService对象
alarm = new AlarmManagerService(context);
//将这个服务注册到系统中
ServiceManager.addService(Context.ALARM_SERVICE, alarm);
......
Slog.i(TAG, "Window Manager");
wm = WindowManagerService.main(context, power,
factoryTest != SystemServer.FACTORY_TEST_LOW_LEVEL,
!firstBoot, onlyCore);
ServiceManager.addService(Context.WINDOW_SERVICE, wm);
.......
looper.loop()
- 总之，在这个线程里面，就是把那些乱七八糟的系统服务都注册好.我之所以说这个进程是吊炸天的进程，是因为Android的几乎所有的核心服务都是在这里注册和启动的。包括但不限于AMS，WMS等等这些日常开发比较贴近的核心服务
但是其实这里只有非常深刻的Binder通信机制，暂且不说