KMC 京都マイクロコンピュータ株式会社

initからapp_processを起動。

init.rc

service zygote /system/bin/app_process -Xzygote /system/bin --zygote --start-system-server
    socket zygote stream 666
    onrestart write /sys/android_power/request_state wake
    onrestart write /sys/power/state on
    onrestart restart media
    onrestart restart netd

frameworks/base/cmds/app_process/app_main.cpp::main

        if (0 == strcmp("--zygote", arg)) {
            bool startSystemServer = (i < argc) ? 
                    strcmp(argv[i], "--start-system-server") == 0 : false;
            setArgv0(argv0, "zygote");
            set_process_name("zygote");
            runtime.start("com.android.internal.os.ZygoteInit",
                startSystemServer);
        } else {

frameworks/base/core/jni/AndroidRuntime.cpp::start

void AndroidRuntime::start(const char* className, const bool startSystemServer)
{
    LOGD("\n>>>>>> AndroidRuntime START %s <<<<<<\n",
            className != NULL ? className : "(unknown)");

    ...
    JNIでcallStatic
    com.android.internal.os.ZygoteInit#main

frameworks/base/core/java/com/android/internal/os/ZygoteInit.java#main

            if (argv[1].equals("true")) {
                startSystemServer();
            } else if (!argv[1].equals("false")) {
                throw new RuntimeException(argv[0] + USAGE_STRING);
            }

frameworks/base/core/java/com/android/internal/os/ZygoteInit.java#startSystemServer

        String args[] = {
            "--setuid=1000",
            "--setgid=1000",
            "--setgroups=1001,1002,1003,1004,1005,1006,1007,1008,1009,1010,3001,3002,3003",
            "--capabilities=130104352,130104352",
            "--runtime-init",
            "--nice-name=system_server",
            "com.android.server.SystemServer",
        };
        ...
        try {
            parsedArgs = new ZygoteConnection.Arguments(args);

            ...
            /* Request to fork the system server process */
            pid = Zygote.forkSystemServer(
                    parsedArgs.uid, parsedArgs.gid,
                    parsedArgs.gids, debugFlags, null,
                    parsedArgs.permittedCapabilities,
                    parsedArgs.effectiveCapabilities);

framesorks/base/services/java/com/android/server/SystemServer.java

SystemServer#main

    public static void main(String[] args) {

        ...        

        System.loadLibrary("android_servers");
        init1(args);  // <-- native method
    }

frameworks/base/services/jni/com_android_server_SystemServer.cpp

static void android_server_SystemServer_init1(JNIEnv* env, jobject clazz)
{
    system_init();
}

frameworks/base/cmds/system_server/library/system_init.cpp

system_init

C++で書いてあるサービスを起動。

• SurfaceFlinger
• SensorService
• AudioFlinger
• MediaPlayerService
• CameraService
• AudioPolicyService

JNIでcallStatic com/android/server/SystemServer#init2

framesorks/base/services/java/com/android/server/SystemServer.java

    public static final void init2() {
        Slog.i(TAG, "Entered the Android system server!");
        Thread thr = new ServerThread();
        thr.setName("android.server.ServerThread");
        thr.start();
    }

ServerThread#run

Javaで書いてあるサービスを起動。

• Entropy Service
• Power Manager
• Activity Manager
• Telephony Registry
• Package Manager
• Account Manager
• Content Manger
• System Content Providers
• Battery Service
• Lights Service
• Vibrator Service
• Alarm Manager
• Init Watchdog
• Window Manager
• Bluetooth Service
• Device Policy
• Status Bar
• Clipboard Service
• Input Method Service
• NetStat Service
• NetworkMnagement Service
• Connectivity Service
• Throttle Service
• Accessibility Manager
• Mount Service
• Notification Manager
• Device Storage Monitor
• Location Manager
• Search Service
• DropBox Service
• Wallpaper Service
• Audio Service
• Headset Observer
• Dock Observer
• USB Observer
• UI Mode Manager Service
• Backup Service
• AppWidget Service
• Recognition Service
• DiskStats Service

これらのサービスは必要に応じてそれぞれスレッドを生成しますが、全てSystemServerのプロセスの中で動いています。

普通のLinuxシステムならデーモンはそれぞれ独立したプロセスになっているのと対照的です。