Java进程鼻祖-zygote

Android知识总结

一、启动zygote进程

zygote是由init进程通过解析 init.zygote.rc 文件而创建的,zygote所对应的可执行程序 app_process,所对应的源文件是 app_main.cpp ,进程名为zygote

system/core/rootdir/init.zygote32.rc(32 位系统)

service zygote /system/bin/app_process -Xzygote /system/bin --zygote --start-system-server
    class main
    socket zygote stream 660 root system
    onrestart write /sys/android_power/request_state wake
    onrestart write /sys/power/state on
    onrestart restart media
    onrestart restart netd
    writepid /dev/cpuset/foreground/tasks

二、执行app_main.cpp中的main方法

启动 zygote 文件的入口函数是 app_main.cpp 中的main方法。
frameworks/base/cmds/app_process/app_main.cpp

int main(int argc, char* const argv[])
{
    if (prctl(PR_SET_NO_NEW_PRIVS, 1, 0, 0, 0) < 0) {
        if (errno != EINVAL) {
            LOG_ALWAYS_FATAL("PR_SET_NO_NEW_PRIVS failed: %s", strerror(errno));
            return 12;
        }
    }
    //创建 runtime 对象
    AppRuntime runtime(argv[0], computeArgBlockSize(argc, argv));
    // Process command line arguments
    // ignore argv[0]
    argc--;
    argv++;
    int i;
    //解析 Zygote 传入的参数
    for (i = 0; i < argc; i++) {
        if (argv[i][0] != '-') {
            break;
        }
        if (argv[i][1] == '-' && argv[i][2] == 0) {
            ++i; // Skip --.
            break;
        }
        runtime.addOption(strdup(argv[i]));
    }

    // Parse runtime arguments.  Stop at first unrecognized option.
    bool zygote = false;
    bool startSystemServer = false;
    bool application = false;
    String8 niceName;
    String8 className;

    ++i;  // Skip unused "parent dir" argument.
    while (i < argc) {
        const char* arg = argv[i++];
        //将zygote标志位置为true
        if (strcmp(arg, "--zygote") == 0) {
            zygote = true;
            niceName = ZYGOTE_NICE_NAME;
        } else if (strcmp(arg, "--start-system-server") == 0) {
            startSystemServer = true;
        } else if (strcmp(arg, "--application") == 0) {
            application = true;
        } else if (strncmp(arg, "--nice-name=", 12) == 0) {
            niceName.setTo(arg + 12);
        } else if (strncmp(arg, "--", 2) != 0) {
            className.setTo(arg);
            break;
        } else {
            --i;
            break;
        }
    }

    Vector<String8> args;
    if (!className.isEmpty()) {
        args.add(application ? String8("application") : String8("tool"));
        runtime.setClassNameAndArgs(className, argc - i, argv + i);
    } else {
        // We're in zygote mode.
        maybeCreateDalvikCache();

        if (startSystemServer) {
            args.add(String8("start-system-server"));
        }

        char prop[PROP_VALUE_MAX];
        if (property_get(ABI_LIST_PROPERTY, prop, NULL) == 0) {
            LOG_ALWAYS_FATAL("app_process: Unable to determine ABI list from property %s.",
                ABI_LIST_PROPERTY);
            return 11;
        }

        String8 abiFlag("--abi-list=");
        abiFlag.append(prop);
        args.add(abiFlag);

        // In zygote mode, pass all remaining arguments to the zygote
        // main() method.
        for (; i < argc; ++i) {
            args.add(String8(argv[i]));
        }
    }

    if (!niceName.isEmpty()) {
        runtime.setArgv0(niceName.string());
        set_process_name(niceName.string());
    }
  
    if (zygote) {
         //运行AndroidRuntime.cpp的start方法
        runtime.start("com.android.internal.os.ZygoteInit", args, zygote);
    } else if (className) {
        //应用 app 启动
        runtime.start("com.android.internal.os.RuntimeInit", args, zygote);
    } else {
        fprintf(stderr, "Error: no class name or --zygote supplied.\n");
        app_usage();
        LOG_ALWAYS_FATAL("app_process: no class name or --zygote supplied.");
        return 10;
    }
}

2.1、AndroidRuntime::start

调用startReg方法来完成jni方法的注册。因为AppRuntime继承AndroidRuntime所以走 AndroidRuntime 的 start 方法
frameworks/base/core/jni/AndroidRuntime.cpp

void AndroidRuntime::start(const char* className, const Vector<String8>& options, bool zygote)
{
    JNIEnv* env;   
    //1、启动虚拟机
    if (startVm(&mJavaVM, &env, zygote, primary_zygote) != 0) {
        return;
    }
    onVmCreated(env);
    //2、 注册jni
    if (startReg(env) < 0) {
        ALOGE("Unable to register all android natives\n");
        return;
    }

    char* slashClassName = toSlashClassName(className != NULL ? className : "");
    jclass startClass = env->FindClass(slashClassName);
    if (startClass == NULL) {
        ALOGE("JavaVM unable to locate class '%s'\n", slashClassName);
        /* keep going */
    } else {
        jmethodID startMeth = env->GetStaticMethodID(startClass, "main",
            "([Ljava/lang/String;)V");
        if (startMeth == NULL) {
            ALOGE("JavaVM unable to find main() in '%s'\n", className);
            /* keep going */
        } else { //3、调用 main@zygoteinit.java,启动 zygote
            env->CallStaticVoidMethod(startClass, startMeth, strArray);

#if 0
            if (env->ExceptionCheck())
                threadExitUncaughtException(env);
#endif
        }
    }
    free(slashClassName);
}

native 层做的事情:

  • 1、初始化运行环境,创建jvm Android的虚拟机 AndroidRuntime ART
  • 2、注册jni
  • 3、调用 zygoteinit.main,进入Java层

三、启动 JVM 虚拟机

int AndroidRuntime::startVm(JavaVM** pJavaVM, JNIEnv** pEnv, bool zygote, bool primary_zygote)
{
    JavaVMInitArgs initArgs;
    char propBuf[PROPERTY_VALUE_MAX];
    char jniOptsBuf[sizeof("-Xjniopts:")-1 + PROPERTY_VALUE_MAX];
    char heapstartsizeOptsBuf[sizeof("-Xms")-1 + PROPERTY_VALUE_MAX];
    char heapsizeOptsBuf[sizeof("-Xmx")-1 + PROPERTY_VALUE_MAX];
    char heapgrowthlimitOptsBuf[sizeof("-XX:HeapGrowthLimit=")-1 + PROPERTY_VALUE_MAX];
    char heapminfreeOptsBuf[sizeof("-XX:HeapMinFree=")-1 + PROPERTY_VALUE_MAX];
    char heapmaxfreeOptsBuf[sizeof("-XX:HeapMaxFree=")-1 + PROPERTY_VALUE_MAX];
    char usejitOptsBuf[sizeof("-Xusejit:")-1 + PROPERTY_VALUE_MAX];
    char jitpthreadpriorityOptsBuf[sizeof("-Xjitpthreadpriority:")-1 + PROPERTY_VALUE_MAX];
    char jitmaxsizeOptsBuf[sizeof("-Xjitmaxsize:")-1 + PROPERTY_VALUE_MAX];
    char jitinitialsizeOptsBuf[sizeof("-Xjitinitialsize:")-1 + PROPERTY_VALUE_MAX];
    char jitthresholdOptsBuf[sizeof("-Xjitthreshold:")-1 + PROPERTY_VALUE_MAX];
    char useJitProfilesOptsBuf[sizeof("-Xjitsaveprofilinginfo:")-1 + PROPERTY_VALUE_MAX];
    char jitprithreadweightOptBuf[sizeof("-Xjitprithreadweight:")-1 + PROPERTY_VALUE_MAX];
    char jittransitionweightOptBuf[sizeof("-Xjittransitionweight:")-1 + PROPERTY_VALUE_MAX];
    char hotstartupsamplesOptsBuf[sizeof("-Xps-hot-startup-method-samples:")-1 + PROPERTY_VALUE_MAX];
   ...
    parseRuntimeOption("dalvik.vm.heapstartsize", heapstartsizeOptsBuf, "-Xms", "4m");
    parseRuntimeOption("dalvik.vm.heapsize", heapsizeOptsBuf, "-Xmx", "16m"); //堆大小
    ...
}

四、注册JNI

/*
 * Register android native functions with the VM.
 */
/*static*/ int AndroidRuntime::startReg(JNIEnv* env)
{
    //创建线程
    androidSetCreateThreadFunc((android_create_thread_fn) javaCreateThreadEtc);

    ALOGV("--- registering native functions ---\n");
    //创建局部引用
    env->PushLocalFrame(200);
    //注册jni方法
    if (register_jni_procs(gRegJNI, NELEM(gRegJNI), env) < 0) {
        env->PopLocalFrame(NULL);
        return -1;
    }
    env->PopLocalFrame(NULL);

    //createJavaThread("fubar", quickTest, (void*) "hello");

    return 0;
}
static int register_jni_procs(const RegJNIRec array[], size_t count, JNIEnv* env)
{
    for (size_t i = 0; i < count; i++) {
        //循环注册jni方法
        if (array[i].mProc(env) < 0) {
#ifndef NDEBUG
            ALOGD("----------!!! %s failed to load\n", array[i].mName);
#endif
            return -1;
        }
    }
    return 0;
}
#ifdef NDEBUG
    #define REG_JNI(name)      { name }
    struct RegJNIRec {
        int (*mProc)(JNIEnv*);
    };
#else
    #define REG_JNI(name)      { name, #name }
    struct RegJNIRec {
        int (*mProc)(JNIEnv*);
        const char* mName;
    };
#endif

//静态注册(系统提供的JNI方法)
//动态注册,一般为自定义的JNI方法
static const RegJNIRec gRegJNI[] = {
    REG_JNI(register_com_android_internal_os_RuntimeInit),
    REG_JNI(register_android_os_SystemClock),
    REG_JNI(register_android_util_EventLog),
    REG_JNI(register_android_util_Log),
    REG_JNI(register_android_content_AssetManager),
    REG_JNI(register_android_content_StringBlock),
    REG_JNI(register_android_content_XmlBlock),
    REG_JNI(register_android_emoji_EmojiFactory),
    REG_JNI(register_android_text_AndroidCharacter),
    REG_JNI(register_android_text_StaticLayout),
    REG_JNI(register_android_text_AndroidBidi),
    REG_JNI(register_android_view_InputDevice),
    REG_JNI(register_android_view_KeyCharacterMap),
    REG_JNI(register_android_os_Process),
    REG_JNI(register_android_os_SystemProperties),
    //注册 binder
    REG_JNI(register_android_os_Binder),
    REG_JNI(register_android_os_Parcel),
    REG_JNI(register_android_nio_utils),
    REG_JNI(register_android_graphics_Graphics),
    REG_JNI(register_android_view_DisplayEventReceiver),
    REG_JNI(register_android_view_RenderNode),
    REG_JNI(register_android_view_RenderNodeAnimator),
    REG_JNI(register_android_view_GraphicBuffer),
    REG_JNI(register_android_view_DisplayListCanvas),
    REG_JNI(register_android_view_HardwareLayer),
    REG_JNI(register_android_view_ThreadedRenderer),
    REG_JNI(register_android_view_Surface),
    REG_JNI(register_android_view_SurfaceControl),
    REG_JNI(register_android_view_SurfaceSession),
    REG_JNI(register_android_view_TextureView),
    REG_JNI(register_com_android_internal_view_animation_NativeInterpolatorFactoryHelper),
    REG_JNI(register_com_google_android_gles_jni_EGLImpl),
    REG_JNI(register_com_google_android_gles_jni_GLImpl),
    REG_JNI(register_android_opengl_jni_EGL14),
    REG_JNI(register_android_opengl_jni_EGLExt),
    REG_JNI(register_android_opengl_jni_GLES10),
    REG_JNI(register_android_opengl_jni_GLES10Ext),
    REG_JNI(register_android_opengl_jni_GLES11),
    REG_JNI(register_android_opengl_jni_GLES11Ext),
    REG_JNI(register_android_opengl_jni_GLES20),
    REG_JNI(register_android_opengl_jni_GLES30),
    REG_JNI(register_android_opengl_jni_GLES31),
    REG_JNI(register_android_opengl_jni_GLES31Ext),

    REG_JNI(register_android_graphics_Bitmap),
    REG_JNI(register_android_graphics_BitmapFactory),
    REG_JNI(register_android_graphics_BitmapRegionDecoder),
    REG_JNI(register_android_graphics_Camera),
    REG_JNI(register_android_graphics_CreateJavaOutputStreamAdaptor),
    REG_JNI(register_android_graphics_Canvas),
    REG_JNI(register_android_graphics_CanvasProperty),
    REG_JNI(register_android_graphics_ColorFilter),
    REG_JNI(register_android_graphics_DrawFilter),
    REG_JNI(register_android_graphics_FontFamily),
    REG_JNI(register_android_graphics_Interpolator),
    REG_JNI(register_android_graphics_LayerRasterizer),
    REG_JNI(register_android_graphics_MaskFilter),
    REG_JNI(register_android_graphics_Matrix),
    REG_JNI(register_android_graphics_Movie),
    REG_JNI(register_android_graphics_NinePatch),
    REG_JNI(register_android_graphics_Paint),
    REG_JNI(register_android_graphics_Path),
    REG_JNI(register_android_graphics_PathMeasure),
    REG_JNI(register_android_graphics_PathEffect),
    REG_JNI(register_android_graphics_Picture),
    REG_JNI(register_android_graphics_PorterDuff),
    REG_JNI(register_android_graphics_Rasterizer),
    REG_JNI(register_android_graphics_Region),
    REG_JNI(register_android_graphics_Shader),
    REG_JNI(register_android_graphics_SurfaceTexture),
    REG_JNI(register_android_graphics_Typeface),
    REG_JNI(register_android_graphics_Xfermode),
    REG_JNI(register_android_graphics_YuvImage),
    REG_JNI(register_android_graphics_pdf_PdfDocument),
    REG_JNI(register_android_graphics_pdf_PdfEditor),
    REG_JNI(register_android_graphics_pdf_PdfRenderer),

    REG_JNI(register_android_database_CursorWindow),
    REG_JNI(register_android_database_SQLiteConnection),
    REG_JNI(register_android_database_SQLiteGlobal),
    REG_JNI(register_android_database_SQLiteDebug),
    REG_JNI(register_android_os_Debug),
    REG_JNI(register_android_os_FileObserver),
    REG_JNI(register_android_os_MessageQueue),
    REG_JNI(register_android_os_SELinux),
    REG_JNI(register_android_os_Trace),
    REG_JNI(register_android_os_UEventObserver),
    REG_JNI(register_android_net_LocalSocketImpl),
    REG_JNI(register_android_net_NetworkUtils),
    REG_JNI(register_android_net_TrafficStats),
    REG_JNI(register_android_os_MemoryFile),
    REG_JNI(register_com_android_internal_os_Zygote),
    REG_JNI(register_com_android_internal_util_VirtualRefBasePtr),
    REG_JNI(register_android_hardware_Camera),
    REG_JNI(register_android_hardware_camera2_CameraMetadata),
    REG_JNI(register_android_hardware_camera2_legacy_LegacyCameraDevice),
    REG_JNI(register_android_hardware_camera2_legacy_PerfMeasurement),
    REG_JNI(register_android_hardware_camera2_DngCreator),
    REG_JNI(register_android_hardware_Radio),
    REG_JNI(register_android_hardware_SensorManager),
    REG_JNI(register_android_hardware_SerialPort),
    REG_JNI(register_android_hardware_SoundTrigger),
    REG_JNI(register_android_hardware_UsbDevice),
    REG_JNI(register_android_hardware_UsbDeviceConnection),
    REG_JNI(register_android_hardware_UsbRequest),
    REG_JNI(register_android_hardware_location_ActivityRecognitionHardware),
    REG_JNI(register_android_media_AudioRecord),
    REG_JNI(register_android_media_AudioSystem),
    REG_JNI(register_android_media_AudioTrack),
    REG_JNI(register_android_media_JetPlayer),
    REG_JNI(register_android_media_RemoteDisplay),
    REG_JNI(register_android_media_ToneGenerator),

    REG_JNI(register_android_opengl_classes),
    REG_JNI(register_android_server_NetworkManagementSocketTagger),
    REG_JNI(register_android_ddm_DdmHandleNativeHeap),
    REG_JNI(register_android_backup_BackupDataInput),
    REG_JNI(register_android_backup_BackupDataOutput),
    REG_JNI(register_android_backup_FileBackupHelperBase),
    REG_JNI(register_android_backup_BackupHelperDispatcher),
    REG_JNI(register_android_app_backup_FullBackup),
    REG_JNI(register_android_app_ActivityThread),
    REG_JNI(register_android_app_NativeActivity),
    REG_JNI(register_android_view_InputChannel),
    REG_JNI(register_android_view_InputEventReceiver),
    REG_JNI(register_android_view_InputEventSender),
    REG_JNI(register_android_view_InputQueue),
    REG_JNI(register_android_view_KeyEvent),
    REG_JNI(register_android_view_MotionEvent),
    REG_JNI(register_android_view_PointerIcon),
    REG_JNI(register_android_view_VelocityTracker),

    REG_JNI(register_android_content_res_ObbScanner),
    REG_JNI(register_android_content_res_Configuration),

    REG_JNI(register_android_animation_PropertyValuesHolder),
    REG_JNI(register_com_android_internal_content_NativeLibraryHelper),
    REG_JNI(register_com_android_internal_net_NetworkStatsFactory),
};

4.1、register_android_os_Binder

已注册register_android_os_Binder为例
frameworks/base/core/jni/android_util_Binder.cpp

int register_android_os_Binder(JNIEnv* env)
{
    if (int_register_android_os_Binder(env) < 0)
        return -1;
    if (int_register_android_os_BinderInternal(env) < 0)
        return -1;
    if (int_register_android_os_BinderProxy(env) < 0)
        return -1;

    jclass clazz = FindClassOrDie(env, "android/util/Log");
    gLogOffsets.mClass = MakeGlobalRefOrDie(env, clazz);
    gLogOffsets.mLogE = GetStaticMethodIDOrDie(env, clazz, "e",
            "(Ljava/lang/String;Ljava/lang/String;Ljava/lang/Throwable;)I");

    clazz = FindClassOrDie(env, "android/os/ParcelFileDescriptor");
    gParcelFileDescriptorOffsets.mClass = MakeGlobalRefOrDie(env, clazz);
    gParcelFileDescriptorOffsets.mConstructor = GetMethodIDOrDie(env, clazz, "<init>",
                                                                 "(Ljava/io/FileDescriptor;)V");

    clazz = FindClassOrDie(env, "android/os/StrictMode");
    gStrictModeCallbackOffsets.mClass = MakeGlobalRefOrDie(env, clazz);
    gStrictModeCallbackOffsets.mCallback = GetStaticMethodIDOrDie(env, clazz,
            "onBinderStrictModePolicyChange", "(I)V");

    return 0;
}
  • int_register_android_os_Binder
static const JNINativeMethod gBinderMethods[] = {
     // java <==> native 关联
    { "getCallingPid", "()I", (void*)android_os_Binder_getCallingPid },
    { "getCallingUid", "()I", (void*)android_os_Binder_getCallingUid },
    { "clearCallingIdentity", "()J", (void*)android_os_Binder_clearCallingIdentity },
    { "restoreCallingIdentity", "(J)V", (void*)android_os_Binder_restoreCallingIdentity },
    { "setThreadStrictModePolicy", "(I)V", (void*)android_os_Binder_setThreadStrictModePolicy },
    { "getThreadStrictModePolicy", "()I", (void*)android_os_Binder_getThreadStrictModePolicy },
    { "flushPendingCommands", "()V", (void*)android_os_Binder_flushPendingCommands },
    { "init", "()V", (void*)android_os_Binder_init },
    { "destroy", "()V", (void*)android_os_Binder_destroy },
    { "blockUntilThreadAvailable", "()V", (void*)android_os_Binder_blockUntilThreadAvailable }
};

const char* const kBinderPathName = "android/os/Binder";

static int int_register_android_os_Binder(JNIEnv* env)
{
    //查找文件 kBinderPathName = "android/os/Binder",返回对应Class对象
    jclass clazz = FindClassOrDie(env, kBinderPathName);
    // 通过gBinderOffsets结构体,保存Java层Binder类的信息,为JNI层访问Java层提供通道
    gBinderOffsets.mClass = MakeGlobalRefOrDie(env, clazz);
    gBinderOffsets.mExecTransact = GetMethodIDOrDie(env, clazz, "execTransact", "(IJJI)Z");
    gBinderOffsets.mObject = GetFieldIDOrDie(env, clazz, "mObject", "J");
    // 通过RegisterMethodsOrDie,将为gBinderMethods数组完成映射关系,从而为Java层访问JNI层提供通道
    return RegisterMethodsOrDie(
        env, kBinderPathName,
        gBinderMethods, NELEM(gBinderMethods));
}
  • int_register_android_os_BinderInternal
static const JNINativeMethod gBinderInternalMethods[] = {
     // java <==> native 关联
    { "getContextObject", "()Landroid/os/IBinder;", (void*)android_os_BinderInternal_getContextObject },
    { "joinThreadPool", "()V", (void*)android_os_BinderInternal_joinThreadPool },
    { "disableBackgroundScheduling", "(Z)V", (void*)android_os_BinderInternal_disableBackgroundScheduling },
    { "handleGc", "()V", (void*)android_os_BinderInternal_handleGc }
};

const char* const kBinderInternalPathName = "com/android/internal/os/BinderInternal";

static int int_register_android_os_BinderInternal(JNIEnv* env)
{
    // 查找文件kBinderInternalPathName ="com/android/internal/os/BinderInternal",返回Class对象
    jclass clazz = FindClassOrDie(env, kBinderInternalPathName);
    // 通过gBinderInternalOffsets,保存Java层BinderInternal类的信息,为JNI层访问java层提供通道
    gBinderInternalOffsets.mClass = MakeGlobalRefOrDie(env, clazz);
    gBinderInternalOffsets.mForceGc = GetStaticMethodIDOrDie(env, clazz, "forceBinderGc", "()V");
    // 通过RegisterMethodsOrDie(),将为gBinderInternalMethods数组完成映射关系,从而为Java层访问JNI层提供通道
    return RegisterMethodsOrDie(
        env, kBinderInternalPathName,
        gBinderInternalMethods, NELEM(gBinderInternalMethods));
}
  • int_register_android_os_BinderProxy
static const JNINativeMethod gBinderProxyMethods[] = {
     // java <==> native 关联
    {"pingBinder",          "()Z", (void*)android_os_BinderProxy_pingBinder},
    {"isBinderAlive",       "()Z", (void*)android_os_BinderProxy_isBinderAlive},
    {"getInterfaceDescriptor", "()Ljava/lang/String;", (void*)android_os_BinderProxy_getInterfaceDescriptor},
    {"transactNative",      "(ILandroid/os/Parcel;Landroid/os/Parcel;I)Z", (void*)android_os_BinderProxy_transact},
    {"linkToDeath",         "(Landroid/os/IBinder$DeathRecipient;I)V", (void*)android_os_BinderProxy_linkToDeath},
    {"unlinkToDeath",       "(Landroid/os/IBinder$DeathRecipient;I)Z", (void*)android_os_BinderProxy_unlinkToDeath},
    {"destroy",             "()V", (void*)android_os_BinderProxy_destroy},
};

const char* const kBinderProxyPathName = "android/os/BinderProxy";

static int int_register_android_os_BinderProxy(JNIEnv* env)
{
    gErrorOffsets.mError = MakeGlobalRefOrDie(env, FindClassOrDie(env, "java/lang/Error"));
    gErrorOffsets.mOutOfMemory =
        MakeGlobalRefOrDie(env, FindClassOrDie(env, "java/lang/OutOfMemoryError"));
    gErrorOffsets.mStackOverflow =
        MakeGlobalRefOrDie(env, FindClassOrDie(env, "java/lang/StackOverflowError"));
    // 查找文件 kBinderProxyPathName = "android/os/BinderProxy",返回对应Class对象
    jclass clazz = FindClassOrDie(env, kBinderProxyPathName);
    // 通过gBinderProxyOffsets,保存Java层BinderProxy类的信息,为JNI层访问Java提供通道
    gBinderProxyOffsets.mClass = MakeGlobalRefOrDie(env, clazz);
    gBinderProxyOffsets.mGetInstance = GetStaticMethodIDOrDie(env, clazz, "getInstance",
            "(JJ)Landroid/os/BinderProxy;");
    gBinderProxyOffsets.mSendDeathNotice =
            GetStaticMethodIDOrDie(env, clazz, "sendDeathNotice",
                                   "(Landroid/os/IBinder$DeathRecipient;Landroid/os/IBinder;)V");
    gBinderProxyOffsets.mNativeData = GetFieldIDOrDie(env, clazz, "mNativeData", "J");

    clazz = FindClassOrDie(env, "java/lang/Class");
    gClassOffsets.mGetName = GetMethodIDOrDie(env, clazz, "getName", "()Ljava/lang/String;");
    // 通过RegisterMethodsOrDie(),将为gBinderProxyMethods数组完成映射关系,从而为Java层访问JNI层提供通道
    return RegisterMethodsOrDie(
        env, kBinderProxyPathName,
        gBinderProxyMethods, NELEM(gBinderProxyMethods));
}

五、启动 zygote(在Java层)


ZygoteInit.java

    public static void main(String[] argv) {
        ZygoteServer zygoteServer = null; //就是一个 socket

        // Mark zygote start. This ensures that thread creation will throw
        // an error.
        ZygoteHooks.startZygoteNoThreadCreation();

        // Zygote goes into its own process group.
        try {
            Os.setpgid(0, 0);
        } catch (ErrnoException ex) {
            throw new RuntimeException("Failed to setpgid(0,0)", ex);
        }

        Runnable caller;
        try {
            // Store now for StatsLogging later.
            final long startTime = SystemClock.elapsedRealtime();
            final boolean isRuntimeRestarted = "1".equals(
                    SystemProperties.get("sys.boot_completed"));

            String bootTimeTag = Process.is64Bit() ? "Zygote64Timing" : "Zygote32Timing";
            TimingsTraceLog bootTimingsTraceLog = new TimingsTraceLog(bootTimeTag,
                    Trace.TRACE_TAG_DALVIK);
            bootTimingsTraceLog.traceBegin("ZygoteInit");
            RuntimeInit.preForkInit();

            boolean startSystemServer = false;
            String zygoteSocketName = "zygote";
            String abiList = null;
            boolean enableLazyPreload = false;
            //解析app_main.cpp传来的参数
            for (int i = 1; i < argv.length; i++) {
                if ("start-system-server".equals(argv[i])) {
                    startSystemServer = true;
                } else if ("--enable-lazy-preload".equals(argv[i])) {
                    enableLazyPreload = true;
                } else if (argv[i].startsWith(ABI_LIST_ARG)) {
                    abiList = argv[i].substring(ABI_LIST_ARG.length());
                } else if (argv[i].startsWith(SOCKET_NAME_ARG)) {
                    zygoteSocketName = argv[i].substring(SOCKET_NAME_ARG.length());
                } else {
                    throw new RuntimeException("Unknown command line argument: " + argv[i]);
                }
            }

            final boolean isPrimaryZygote = zygoteSocketName.equals(Zygote.PRIMARY_SOCKET_NAME);
            if (!isRuntimeRestarted) {
                if (isPrimaryZygote) {
                    FrameworkStatsLog.write(FrameworkStatsLog.BOOT_TIME_EVENT_ELAPSED_TIME_REPORTED,
                            BOOT_TIME_EVENT_ELAPSED_TIME__EVENT__ZYGOTE_INIT_START,
                            startTime);
                } else if (zygoteSocketName.equals(Zygote.SECONDARY_SOCKET_NAME)) {
                    FrameworkStatsLog.write(FrameworkStatsLog.BOOT_TIME_EVENT_ELAPSED_TIME_REPORTED,
                            BOOT_TIME_EVENT_ELAPSED_TIME__EVENT__SECONDARY_ZYGOTE_INIT_START,
                            startTime);
                }
            }

            if (abiList == null) {
                throw new RuntimeException("No ABI list supplied.");
            }

            // In some configurations, we avoid preloading resources and classes eagerly.
            // In such cases, we will preload things prior to our first fork.
            if (!enableLazyPreload) {
                bootTimingsTraceLog.traceBegin("ZygotePreload");
                EventLog.writeEvent(LOG_BOOT_PROGRESS_PRELOAD_START,
                        SystemClock.uptimeMillis());
        
                //预加载进程的资源和类,加快进程的启动             
                preload(bootTimingsTraceLog);
                EventLog.writeEvent(LOG_BOOT_PROGRESS_PRELOAD_END,
                        SystemClock.uptimeMillis());
                bootTimingsTraceLog.traceEnd(); // ZygotePreload
            }

            // Do an initial gc to clean up after startup
            bootTimingsTraceLog.traceBegin("PostZygoteInitGC");
            gcAndFinalize();
            bootTimingsTraceLog.traceEnd(); // PostZygoteInitGC

            bootTimingsTraceLog.traceEnd(); // ZygoteInit

            Zygote.initNativeState(isPrimaryZygote);

            ZygoteHooks.stopZygoteNoThreadCreation();
            //主要是初始化 socket
            zygoteServer = new ZygoteServer(isPrimaryZygote);

            if (startSystemServer) {
                 //开启SystemServer进程,这是受精卵进程的第一次分裂
                Runnable r = forkSystemServer(abiList, zygoteSocketName, zygoteServer);

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

            Log.i(TAG, "Accepting command socket connections");

            // The select loop returns early in the child process after a fork and
            // loops forever in the zygote.
            //启动一个死循环监听来自Client端的消息,即接收AMS传过来的消息
            //接收到AMS信息后,创建APP进程
            //反射执行 ActivityThread@main()方法
            caller = zygoteServer.runSelectLoop(abiList);
        } catch (Throwable ex) {
            Log.e(TAG, "System zygote died with exception", ex);
            throw ex;
        } finally {
        //关闭SystemServer的Socket
            if (zygoteServer != null) {
                zygoteServer.closeServerSocket();
            }
        }

        //这里捕获这个异常调用MethodAndArgsCaller的run方法
        if (caller != null) {
            caller.run();
        }
    }

ZygoteInit的main方法大概就做了上面六件事情

  • 1、创建ZygoteServer,在Android O上把与Socket的操作都封装到了ZygoteServer类中;
  • 2、解析app_main.cpp传来的参数。
  • 3、创建一个Server端的Socket,作用是当Zygote进程将SystemServer进程启动后,就会在这个Socket上来等待ActivityManagerService请求,即请求创建我们自己APP应用程序进程;
  • 4、预加载类和资源,包括颜色啊,R文件,drawable、类等;
  • 5、启动system_server进程,这是上层framework的运行载体,ActivityManagerService就是运行在这个进程里面的;
  • 6、开启一个循环,等待着接收ActivityManagerService的请求,随时待命,当接收到创建新进程的请求时立即唤醒并执行相应工作;

五、总结

zygote进程启动
zygote执行流程
zygote的预加载

zygote 主要时进行 java 层于native 层交互的桥梁。是java成的鼻祖,会 fork 一个大孩子 SystemServer 进程,当我们启动APP时,SystemServer 会通过 AMS 通知到 zygote 来 fork 一个APP进程。

zygote总结:
native:

  • 1、初始化运行环境,创建jvm Android的虚拟机。在zygote进程中创建,虚拟机实现的功能就是内存管理
  • 2、注册 JNI桥梁,用于ntive和java之间的通信
  • 3、调用 zygoteinit.main,启动 zygote进入Java层

java:

  • 1、预加载 -- 加快进程启动
  • 2、创建 socket ,让别人通知我消息 fork 进程
  • 3、通过fork创建 SystemServer 进程
  • 3、循环等待,等待AMS的通知,创建对应的进程

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