Android Zygote进程启动分析

private static void registerZygoteSocket(String socketName) {
    if (sServerSocket == null) {
        int fileDesc;
        final String fullSocketName = ANDROID_SOCKET_PREFIX + socketName;
        try {
            String env = System.getenv(fullSocketName);
            fileDesc = Integer.parseInt(env);
        } catch (RuntimeException ex) {
            throw new RuntimeException(fullSocketName + " unset or invalid", ex);
        }

        try {
            sServerSocket = new LocalServerSocket(
                    createFileDescriptor(fileDesc));
        } catch (IOException ex) {
            throw new RuntimeException(
                    "Error binding to local socket ‘" + fileDesc + "‘", ex);
        }
    }
}

  static void preload() {
    Log.d(TAG, "begin preload");
    preloadClasses();
    preloadResources();
    preloadOpenGL();
    preloadSharedLibraries();
    // Ask the WebViewFactory to do any initialization that must run in the zygote process,
    // for memory sharing purposes.
    WebViewFactory.prepareWebViewInZygote();
    Log.d(TAG, "end preload");
}

private static void preloadClasses() {
        //.......省略代码
        is = new FileInputStream(PRELOADED_CLASSES);
        // ......省略代码
        BufferedReader br
            = new BufferedReader(new InputStreamReader(is), 256);

        int count = 0;
        String line;
        while ((line = br.readLine()) != null) {
            // Skip comments and blank lines.
            line = line.trim();
            if (line.startsWith("#") || line.equals("")) {
                continue;
            }

            try {
                if (false) {
                    Log.v(TAG, "Preloading " + line + "...");
                }
                Class.forName(line);
                if (Debug.getGlobalAllocSize() > PRELOAD_GC_THRESHOLD) {
                    if (false) {
                        Log.v(TAG,
                            " GC at " + Debug.getGlobalAllocSize());
                    }
                    System.gc();
                    runtime.runFinalizationSync();
                    Debug.resetGlobalAllocSize();
                }
                count++;
                //......省略代码

            }

         //......省略代码
}

private static void preloadResources() {
    final VMRuntime runtime = VMRuntime.getRuntime();

    Debug.startAllocCounting();
    try {
        System.gc();
        runtime.runFinalizationSync();
        mResources = Resources.getSystem();
        mResources.startPreloading();
        if (PRELOAD_RESOURCES) {
            Log.i(TAG, "Preloading resources...");

            long startTime = SystemClock.uptimeMillis();
            TypedArray ar = mResources.obtainTypedArray(
                    com.android.internal.R.array.preloaded_drawables);
            int N = preloadDrawables(runtime, ar);
            ar.recycle();
            Log.i(TAG, "...preloaded " + N + " resources in "
                    + (SystemClock.uptimeMillis()-startTime) + "ms.");

            startTime = SystemClock.uptimeMillis();
            ar = mResources.obtainTypedArray(
                    com.android.internal.R.array.preloaded_color_state_lists);
            N = preloadColorStateLists(runtime, ar);
            ar.recycle();
            Log.i(TAG, "...preloaded " + N + " resources in "
                    + (SystemClock.uptimeMillis()-startTime) + "ms.");
        }
        mResources.finishPreloading();
    } catch (RuntimeException e) {
        Log.w(TAG, "Failure preloading resources", e);
    } finally {
        Debug.stopAllocCounting();
    }
}

 private static void runSelectLoop(String abiList) throws MethodAndArgsCaller {
    ArrayList<FileDescriptor> fds = new ArrayList<FileDescriptor>();
    ArrayList<ZygoteConnection> peers = new ArrayList<ZygoteConnection>();
    FileDescriptor[] fdArray = new FileDescriptor[4];

    fds.add(sServerSocket.getFileDescriptor());
    peers.add(null);

    int loopCount = GC_LOOP_COUNT;
    while (true) {
        int index;

        /*
         * Call gc() before we block in select().
         * It‘s work that has to be done anyway, and it‘s better
         * to avoid making every child do it.  It will also
         * madvise() any free memory as a side-effect.
         *
         * Don‘t call it every time, because walking the entire
         * heap is a lot of overhead to free a few hundred bytes.
         */
        if (loopCount <= 0) {
            gc();
            loopCount = GC_LOOP_COUNT;
        } else {
            loopCount--;
        }


        try {
            fdArray = fds.toArray(fdArray);
            index = selectReadable(fdArray);
        } catch (IOException ex) {
            throw new RuntimeException("Error in select()", ex);
        }

        if (index < 0) {
            throw new RuntimeException("Error in select()");
        } else if (index == 0) {
            ZygoteConnection newPeer = acceptCommandPeer(abiList);
            peers.add(newPeer);
            fds.add(newPeer.getFileDescriptor());
        } else {
            boolean done;
            /*开始读取client发出的命令*/
            done = peers.get(index).runOnce();

            if (done) {
                peers.remove(index);
                fds.remove(index);
            }
        }
    }
}