android8.1啟動程序(六) zygote行程分析2

次部分承接上一篇文章https://blog.csdn.net/we1less/article/details/116139142?spm=1001.2014.3001.5501

registerServerSocket(socketName) AOSP/frameworks/base/core/java/com/android/internal/os/ZygoteServer.java

void registerServerSocket(String socketName) {
    if (mServerSocket == 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 {
            FileDescriptor fd = new FileDescriptor();
            fd.setInt$(fileDesc);
            mServerSocket = new LocalServerSocket(fd);
        } catch (IOException ex) {
            throw new RuntimeException(
                    "Error binding to local socket '" + fileDesc + "'", ex);
        }
    }
}

final String fullSocketName = ANDROID_SOCKET_PREFIX + socketName;

【1】 拼接socker名稱 ANDROID_SOCKET_zygote

String env = System.getenv(fullSocketName);

【2】得到socket的環境變數的值

mServerSocket = new LocalServerSocket(fd);

【3】創建服務器端socket并將檔案運算子作為引數傳遞進去 在zygote行程將systemserver行程啟動后就會在你這個服務器端的socket上等待AMS請求zygote行程來創建新的行程

關于socket這里附上一個文章https://www.cnblogs.com/zijianlu/archive/2013/04/18/3028090.html具體可以參考看看

preload(bootTimingsTraceLog) AOSP/frameworks/base/core/java/com/android/internal/os/ZygoteInit.java

static void preload(TimingsTraceLog bootTimingsTraceLog) {
        Log.d(TAG, "begin preload");
        ...
        preloadClasses();
        ...
        preloadResources();
        ...
        nativePreloadAppProcessHALs();
        ...
        preloadOpenGL();
        ...
        preloadSharedLibraries();
        ...
        preloadTextResources();
        ...
        warmUpJcaProviders();
        ...
    }

【1】預加載位于/system/etc/preloaded-classes檔案中的類

【2】預加載drawble和color的資源資訊AOSP/frameworks/base/core/res/res/values/arrays.xml

drawble : preloaded_drawables

color : preloaded_color_state_lists

【3】通過JNI呼叫，預加載底層相關的資源

【4】預加載OpenGL資源

【5】預加載共享庫："android","compiler_rt","jnigraphics"

【6】預加載文本連接符資源

【7】zygote中，記憶體共享行程

通過【1】【2】步驟的預加載可以使繼承自zygote的行程預加載系統檔案從而使得行程啟動更快

啟動systemserver AOSP/frameworks/base/core/java/com/android/internal/os/ZygoteInit.java

if (startSystemServer) {
    Runnable r = forkSystemServer(abiList, socketName, zygoteServer);

    // {@code r == null} in the parent (zygote) process, and {@code r != null} in the
    // child (system_server) process.
    if (r != null) {
        r.run();
        return;
    }
}

【1】forkSystemServer 父行程分支回傳null 子行程分支回傳 handleSystemServerProcess并回傳回去最終呼叫了run()方法 關于具體systemserver啟動會在后面單獨開一篇文章去分析到這里只需要知道啟動了systemserver就好

【2】Zygote.forkSystemServer 其內部會呼叫nativeForkSystemServer方法，這個native方法最侄訓通過fork()方法創建當前行程的一個子行程 對于fork()方法這里給出一篇文章有興趣的可以參考看看

https://www.cnblogs.com/coolgestar02/archive/2011/04/28/2032018.html 總之fork函式最終在父行程的回傳值是子行程的pid，而在子行程回傳的則是0

private static Runnable forkSystemServer(String abiList, String socketName,
            ZygoteServer zygoteServer) {
        ...
            /* Request to fork the system server process */
            pid = Zygote.forkSystemServer(
                    parsedArgs.uid, parsedArgs.gid,
                    parsedArgs.gids,
                    parsedArgs.debugFlags,
                    null,
                    parsedArgs.permittedCapabilities,
                    parsedArgs.effectiveCapabilities);
        } catch (IllegalArgumentException ex) {
            throw new RuntimeException(ex);
        }

        /* For child process */
        if (pid == 0) {
            if (hasSecondZygote(abiList)) {
                waitForSecondaryZygote(socketName);
            }

            zygoteServer.closeServerSocket();
            return handleSystemServerProcess(parsedArgs);
        }

        return null;
    }

runSelectLoop(abiList) AOSP/frameworks/base/core/java/com/android/internal/os/ZygoteServer.java

Zygote完成了Java的初始作業后，便呼叫runSelectLoop來讓自己無限回圈等待，如果收到子孫后臺的請求，它便會醒來為他們作業，

Runnable runSelectLoop(String abiList) {
    ...
    fds.add(mServerSocket.getFileDescriptor());
    ...
    while (true) {
        StructPollfd[] pollFds = new StructPollfd[fds.size()];
        for (int i = 0; i < pollFds.length; ++i) {
            pollFds[i] = new StructPollfd();
            pollFds[i].fd = fds.get(i);
            ...
        }
        try {
            Os.poll(pollFds, -1);
        } catch (ErrnoException ex) {
            throw new RuntimeException("poll failed", ex);
        }
        for (int i = pollFds.length - 1; i >= 0; --i) {
            if ((pollFds[i].revents & POLLIN) == 0) {
                continue;
            }

            if (i == 0) {
                ZygoteConnection newPeer = acceptCommandPeer(abiList);
                peers.add(newPeer);
                fds.add(newPeer.getFileDesciptor());
            } else {
                    try {
                        ZygoteConnection connection = peers.get(i);
                        final Runnable command = connection.processOneCommand(this);
                    ...
                        if (connection.isClosedByPeer()) {
                            connection.closeSocket();
                            peers.remove(i);
                            fds.remove(i);
                        }
                    }
                } catch (Exception e) {
                    ...
                }
            }
        }
    }
}

【1】fds.add(mServerSocket.getFileDescriptor()); fds[0]為mServerSocket，即mServerSocket為位于zygote行程中的socket服務端

【2】Os.poll(pollFds, -1); 查詢輪訓狀態，當pollFdd有事件到來則往下執行，否則阻塞在這里

【3】if (i == 0) { ZygoteConnection newPeer = acceptCommandPeer(abiList); peers.add(newPeer); fds.add(newPeer.getFileDesciptor());

客戶端第一次請求服務端，服務端呼叫accept與客戶端建立連接，客戶端在zygote以ZygoteConnection物件表示

【4】else { try { ZygoteConnection connection = peers.get(i); final Runnable command = connection.processOneCommand(this);

經過上個if操作后，客戶端與服務端已經建立連接，并開始發送資料 peers.get(index) 取得發送資料客戶端的 ZygoteConnection 物件 然后呼叫 processOneCommand(this) 方法來出具具體請求

如果 i==0 表示說明服務端socket已經于客戶端連接上了 換句話說就是當前zygote行程已經于AMS連接上了

如果 i！=0 表示AMS向zygote行程發送一個創建應用行程的請求 再呼叫 processOneCommand(this) 方法fork出一個新的行程

【5】fds.remove(i); 處理完則從fds中移除該檔案描述符

processOneCommand() AOSP/frameworks/base/core/java/com/android/internal/os/ZygoteConnection.java

在這里fork出一個子行程回傳handleChildProc 父行程執行handleParentProc

pid = Zygote.forkAndSpecialize(parsedArgs.uid, parsedArgs.gid, parsedArgs.gids,
        parsedArgs.debugFlags, rlimits, parsedArgs.mountExternal, parsedArgs.seInfo,
        parsedArgs.niceName, fdsToClose, fdsToIgnore, parsedArgs.instructionSet,
        parsedArgs.appDataDir);

try {
    if (pid == 0) {
        // in child
        zygoteServer.setForkChild();

        zygoteServer.closeServerSocket();
        IoUtils.closeQuietly(serverPipeFd);
        serverPipeFd = null;

        return handleChildProc(parsedArgs, descriptors, childPipeFd);
    } else {
        // In the parent. A pid < 0 indicates a failure and will be handled in
        // handleParentProc.
        IoUtils.closeQuietly(childPipeFd);
        childPipeFd = null;
        handleParentProc(pid, descriptors, serverPipeFd);
        return null;
    }