android java代码的启动：app_process

曾经终败给现在 2022-08-08 05:25 485阅读 0赞

在android上，如果你直接用dalivik去加载framework.jar，你会发现里面的大部分native方法无法使用。同时，在/init.rc里面，你也找不到dalvikvm。在ps列表，也没有dalvikvm。那android是怎么启动java程序的呢？

在android上，java程序是通过app\_process启动的。在/init.rc里面，有如下一段代码：

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

app\_process的命令行参数如下：

app\_process \[java-options\] cmd-dir start-class-name \[options\]

因此，init.rc里面的各个参数的对应关系为：

\-Xzygote： java-options,这些参数会传给dalvik，这些参数必须以-开头，一旦遇到不是以-开头的或者--，代表java-options结束。

/system/bin：cmd-dir，也就是当前目录，文件操作的父路径将为此路径。

start-class-name:空

\--zygote --start-system-server:选项。

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); \} else \{ set\_process\_name(argv0); runtime.mClassName = arg; // Remainder of args get passed to startup class main() runtime.mArgC = argc-i; runtime.mArgV = argv+i; LOGV("App process is starting with pid=%d, class=%s./n", getpid(), runtime.getClassName()); runtime.start(); \} \}

从app\_process的main函数（在app\_main.cpp里面）可以看出，app\_process有两种启动方式：一种是init.rc里面的这种方式，这种方式将会以zygote模式启动com.android.internal.os.ZygoteInit，并将进程名称改为zygote；另外一种是以非zygote模拟启动com.android.internal.os.RuntimeInit，并调用它的main方法，main的最后会执行finishInit，finishInit是一个native方法，这个方法会调用app\_process的onStarted方法，在onStarted里面将会调用真正要执行的class。

无论app\_process，它都将会调用frameworks/base/core/jni/AndroidRuntime.cpp里面的start

方法（496行）。这 个start方法会根据android属性系统设置dalvik的参数，并初始化java代码的native方法，最终启动dalvik。需要注意的是，java代码的大部分native方法（差不多80%）都是在这里面初始化的,这些初始化代码会检查java代码的正确性（例如是否有对应的native方法，是否有需要的属性等），在初始化过程中，任何一步的错误都将导致进程退出。整个native方法初始化过程如下：start（AndroidRuntime.cpp，766行）->startReg(AndroidRuntime.cpp，1136行)-> register\_jni\_procs(AndroidRuntime.cpp，1011行)。初始化的java class有（AndroidRuntime.cpp，1018行）：

static const RegJNIRec gRegJNI\[\] = \{ REG\_JNI(register\_android\_debug\_JNITest), 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\_util\_FloatMath), REG\_JNI(register\_android\_text\_format\_Time), REG\_JNI(register\_android\_pim\_EventRecurrence), 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\_security\_Md5MessageDigest), REG\_JNI(register\_android\_text\_AndroidCharacter), REG\_JNI(register\_android\_text\_KeyCharacterMap), REG\_JNI(register\_android\_os\_Process), REG\_JNI(register\_android\_os\_Binder), REG\_JNI(register\_android\_os\_Hardware), REG\_JNI(register\_android\_view\_Display), REG\_JNI(register\_android\_nio\_utils), REG\_JNI(register\_android\_graphics\_PixelFormat), REG\_JNI(register\_android\_graphics\_Graphics), REG\_JNI(register\_android\_view\_Surface), REG\_JNI(register\_android\_view\_ViewRoot), REG\_JNI(register\_com\_google\_android\_gles\_jni\_EGLImpl), REG\_JNI(register\_com\_google\_android\_gles\_jni\_GLImpl), REG\_JNI(register\_android\_graphics\_Bitmap), REG\_JNI(register\_android\_graphics\_BitmapFactory), REG\_JNI(register\_android\_graphics\_Camera), REG\_JNI(register\_android\_graphics\_Canvas), REG\_JNI(register\_android\_graphics\_ColorFilter), REG\_JNI(register\_android\_graphics\_DrawFilter), 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\_Typeface), REG\_JNI(register\_android\_graphics\_Xfermode), REG\_JNI(register\_com\_android\_internal\_graphics\_NativeUtils), REG\_JNI(register\_android\_database\_CursorWindow), REG\_JNI(register\_android\_database\_SQLiteDatabase), REG\_JNI(register\_android\_database\_SQLiteDebug), REG\_JNI(register\_android\_database\_SQLiteProgram), REG\_JNI(register\_android\_database\_SQLiteQuery), REG\_JNI(register\_android\_database\_SQLiteStatement), REG\_JNI(register\_android\_os\_Debug), REG\_JNI(register\_android\_os\_Exec), REG\_JNI(register\_android\_os\_FileObserver), REG\_JNI(register\_android\_os\_FileUtils), REG\_JNI(register\_android\_os\_ParcelFileDescriptor), REG\_JNI(register\_android\_os\_Power), REG\_JNI(register\_android\_os\_StatFs), REG\_JNI(register\_android\_os\_SystemProperties), REG\_JNI(register\_android\_os\_UEventObserver), REG\_JNI(register\_android\_net\_LocalSocketImpl), REG\_JNI(register\_android\_net\_NetworkUtils), REG\_JNI(register\_android\_net\_wifi\_WifiManager), REG\_JNI(register\_android\_os\_MemoryFile), REG\_JNI(register\_com\_android\_internal\_os\_ZygoteInit), REG\_JNI(register\_android\_hardware\_Camera), REG\_JNI(register\_android\_hardware\_SensorManager), 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\_ToneGenerator), REG\_JNI(register\_android\_opengl\_classes), REG\_JNI(register\_android\_bluetooth\_Database), REG\_JNI(register\_android\_bluetooth\_HeadsetBase), REG\_JNI(register\_android\_bluetooth\_BluetoothAudioGateway), REG\_JNI(register\_android\_bluetooth\_RfcommSocket), REG\_JNI(register\_android\_bluetooth\_ScoSocket), REG\_JNI(register\_android\_server\_BluetoothDeviceService), REG\_JNI(register\_android\_server\_BluetoothEventLoop), REG\_JNI(register\_android\_server\_BluetoothA2dpService), REG\_JNI(register\_android\_message\_digest\_sha1), REG\_JNI(register\_android\_ddm\_DdmHandleNativeHeap), REG\_JNI(register\_android\_util\_Base64), REG\_JNI(register\_android\_location\_GpsLocationProvider), \};

这些初始化的native方法是java代码与底层服务打交道的接口，因此我们必须初始化这些方法。

以app\_process启动java class的另外一个好处是它会初始化IBinder，这样就可以在java代码和jni代码里面接收IBinder消息。