にもり私的記録
--BURN CALORIES, NOT FUEL--

_ く〜っ, 昨日より寒い!!!! よ〜く考えると当たり前なんだけど, スピードは出ないし疲れる上りをがんばるより, らく〜にスピードを出せる下りをがんばる方が時間を短縮できる.

_ zygote 起動

カーネルが起動して最初にコールされるのが, init.rc なのだが, その中で, 最初の(というか, system server?)zygote が起動する. 起動スクリプトはこんな感じ.

system/core/rootdir/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

app_process で zygote を起動させてます. app_process は zygote 以外のアプリも起動出来るみたい. am も内部で app_process をコールしているよ. ココでのポイントは `--start-system-server' を追加しているって事です. app_process の中身は...

frameworks/base/cmds/app_process/app_main.cpp:
int main(int argc, const char* const argv[])
{
    AppRuntime runtime;
 
    // Next arg is startup classname or "--zygote"
    if (i < argc) {
        arg = argv[i++];
        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);
        }
    }
}

runtime.start()で ZygoteInit をコールしていることが分かる. AppRuntime は AndroidRuntime を継承しているので, AndroidRuntime を見ると...

frameworks/base/core/jni/AndroidRuntime.cpp:
/*
 * Start the Android runtime.  This involves starting the virtual machine
 * and calling the "static void main(String[] args)" method in the class
 * named by "className".
 */
void AndroidRuntime::start(const char* className, const bool startSystemServer)
{
    startClass = env->FindClass(slashClassName);
    if (startClass == NULL) {
        LOGE("JavaVM unable to locate class '%s'\n", slashClassName);
        /* keep going */
    } else {
        startMeth = env->GetStaticMethodID(startClass, "main",
            "([Ljava/lang/String;)V");
        if (startMeth == NULL) {
            LOGE("JavaVM unable to find main() in '%s'\n", className);
            /* keep going */
        }
    }
}

JNI でcom.android.internal.os.ZygoteInit#main() をコールしていることが分かる.

frameworks/base/core/java/com/android/internal/os/ZygoteInit.java:
/**
 * Startup class for the zygote process.
 *
 * Pre-initializes some classes, and then waits for commands on a UNIX domain
 * socket. Based on these commands, forks of child processes that inherit
 * the initial state of the VM.
 *
 * Please see {@link ZygoteConnection.Arguments} for documentation on the
 * client protocol.
 *
 * @hide
 */
public class ZygoteInit {
    public static void main(String argv[]) {
        try {
            // Do an initial gc to clean up after startup
            gc();
 
            if (argv[1].equals("true")) {
                startSystemServer();
            }
       }
    }
    /**
     * Prepare the arguments and fork for the system server process.
     */
    private static boolean startSystemServer()
            throws MethodAndArgsCaller, RuntimeException {
        /* Hardcoded command line to start the system server */
        String args[] = {
            "--setuid=1000",
            "--setgid=1000",
            "--setgroups=1001,1002,1003,1004,1005,1006,1007,1008,1009,1010,3001,3002,3003",
            "--capabilities=130104352,130104352",
            "--runtime-init",
            "--nice-name=system_server",
            "com.android.server.SystemServer",
        };
 
        int pid;
 
        try {
             /* Request to fork the system server process */
            pid = Zygote.forkSystemServer(
                    parsedArgs.uid, parsedArgs.gid,
                    parsedArgs.gids, debugFlags, null);
        }
    }
}

main() -> startSystemServer()ときて, Zygote#forkSystemServer()の中で fork() が呼ばれるよ. これを見ると zygote の UID は 1000 のようです. そうそう, zygote のやりとりにはソケットを使っているみたいよ.

dalvik/libcore/dalvik/src/main/java/dalvik/system/Zygote.java;
package dalvik.system;
public class Zygote {
    /**
     * Special method to start the system server process. In addition to the
     * common actions performed in forkAndSpecialize, the pid of the child
     * process is recorded such that the death of the child process will cause 
     * zygote to exit.
     */
    native public static int forkSystemServer(int uid, int gid, 
            int[] gids, int debugFlags, int[][] rlimits);
 
    /**
     * Special method to start the system server process.
     * @deprecated use {@link Zygote#forkSystemServer(int, int, int[], int, int[][])}
     */
    @Deprecated
    public static int forkSystemServer(int uid, int gid, int[] gids,
            boolean enableDebugger, int[][] rlimits) {
        int debugFlags = enableDebugger ? DEBUG_ENABLE_DEBUGGER : 0;
        return forkAndSpecialize(uid, gid, gids, debugFlags, rlimits);
    }}

ココがちょっぴりわからない. どっちがコールされるの？ forkSystemServer()にしても forkAndSpecialize()にしても, fork()がこーるされるんだけどね.

dalvik/vm/native/dalvik_system_Zygote.c:
static void Dalvik_dalvik_system_Zygote_forkSystemServer(
        const u4* args, JValue* pResult)
{
    pid_t pid;
    pid = forkAndSpecializeCommon(args);
 
    RETURN_INT(pid);
}
static void Dalvik_dalvik_system_Zygote_forkAndSpecialize(const u4* args,
    JValue* pResult)
{
    pid_t pid;
 
    pid = forkAndSpecializeCommon(args);
 
    RETURN_INT(pid);
}
/* 
 * Utility routine to fork zygote and specialize the child process.
 */
static pid_t forkAndSpecializeCommon(const u4* args)
{
    pid_t pid;
 
    dvmDumpLoaderStats("zygote");
    pid = fork();
 
    return pid;
}

forkSystemServer()なのに Dalvik_dalvik_system_Zygote_forkSystemServer()かとゆーと, これも JNI なんだと思う(ここんところはちょっと自信なし).

dalvik/vm/native/dalvik_system_Zygote.c:
const DalvikNativeMethod dvm_dalvik_system_Zygote[] = {
    { "fork",            "()I",
        Dalvik_dalvik_system_Zygote_fork },
    { "forkAndSpecialize",            "(II[II[[I)I",
        Dalvik_dalvik_system_Zygote_forkAndSpecialize },
    { "forkSystemServer",            "(II[II[[I)I",
        Dalvik_dalvik_system_Zygote_forkSystemServer },
    { NULL, NULL, NULL },
};
dalvik/vm/native/InternalNative.c:
/*
 * Set of classes for which we provide methods.
 *
 * The last field, classNameHash, is filled in at startup.
 */
static DalvikNativeClass gDvmNativeMethodSet[] = {
    { "Ldalvik/system/Zygote;",           dvm_dalvik_system_Zygote, 0 },
}