android源码分析之Runtime的初始化.doc

android源码分析之Runtime的初始化Android运行时作为android架构的一部分，起着非常重要的作用，它和核心库(Core Libraries)组成了Android运行时库层。本文将依据android源码对AndroidRuntime(android运行时)的建立过程进行分析。1、Android架构中的AndroidRuntimeandroid采用的是层次化系统架构，它的架构图如下：由架构图可知，AndroidRuntime处于Linux内核层以及应用框架层中间，而Java的运行环境依赖于Java虚拟机，所以AndroidRuntime对于android系统非常重要。Init进程是Linux环境下非常重要的一个进程，而Zygote进程是Java环境下的第一个进程，所有其他的Java环境下的进程都是由Zygote进程来进行fork的，而init进程在启动Zygote进程之后，初始化Zygote进程之前，会先进行AndroidRuntime的启动和环境建立，下文将对此过程进行详细分析。2、init进程分析init进程作为linux启动过程中的一个重要的进程，它主要负责文件系统的挂载，属性的初始化，各种配置的加载启动以及Action触发，Service的启动，而Zygote作为Java环境下的服务进程，也在Init.rc中进行了配置，而init进程是由main函数进行触发的，其main函数如下：/Init.cppint main(int argc, char *argv) . /清除umask默认属性 umask(); add_environment(PATH,_PATH_DEFPATH); /判断是不是初始化的第一阶段 bool is_first_stage = (arg = 1)|(strcmp(argv1,-second-stage)!=0); if(is_first_stage) /进行系统文件系统等的挂载 mount(tmpfs,/dev,tmpfs,MS_NOSUID,mode=0755); mkdir(/dev/pts,0755); mkdir(/dev/socket,0755); mount(devpts,/dev/pts,devpts,0,NULL); mount(proc,/proc,proc,0,NULL); mount(sysfs,/sys,sysfs,0,NULL); open_devull_stdio(); /klog初始化 klog_init(); klog_set_level(KLOG_NOTICE_LEVEL); if(!is_first_stage) /关闭/dev/.booting文件的相关权限 close(/dev/.booting,O_WRONLY|O_WCREAT|O_CLOEXEC,000); /初始化部分属性 property_init(); /先初始化DT，因为DT的属性集的优先级高于comand line process_kernel_dt(); /处理内核命令行 process_kernel_cmdline; /导出内核变量 export_kernel_boot_props(); . /初始化信号量 signal_handler_init(); property_load_boot_defaults(); /开启属性服务 start_property_service(); /解析/init.rc文件 init_parse_config_file(/init.rc); . 此处的代码与android 4.4等，在代码上有略微的差别，但是基本的操作还是一样的，首先进行一些属性的初始化，内核命令行等以及信号量的初始化，最后再启动属性服务以及对init.rc文件进行解析，所以，接下来分析Init.rc文件：/Init.rcimport /init.environ.rcimport /init.usb.rcimport /init.$ro.hardware.rcimport /init.$ro.zygote.rcimport /init.trace.rc.由代码可知，与android4.4等有明显的差别，此处采用导入.rc文件的方式来初始化相应模块，此处分析zygote模块，对于android6.0来说，它提供了多个zygote相关的.rc文件，有Init.zygote32.rc、Init.zygote32_64.rc、Init.zygote64.rc、Init.zygote64_32.rc等，本文分析Init.zygote32.rc，其他流程是一样的，但是在源码中，只发现了Init.zygote32.rc的相关实现。 看Init.zygote32.rc文件：/Init.zygote32.rcservice 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由代码可知，它将会执行/system/bin/app_process，而后面的是它的参数，请注意zygote和start-system-server参数，后面将会分析到，而对于/system/bin/app_process的实现app_main.cpp(frameworks/base/cmds/app_process)，它的配置在frameworks/base/cmds/app_process目录下的Android.mk文件中：/Android.mk(frameworks/base/cmds/app_process)LOCAL_PATH = $(call my-dir)app_process_common-shared_libs:= libwilhelminclude $(CLEAR_VARS)#看，app_process命令绑定的源码就是该目录下的app_main.cppLOCAL_SRC_FILES:= app_main.cpp.所以，app_process命令绑定的源码实现就是app_main.cpp，在解析Init.zygote32.rc文件的时候，会调用到它的main函数，即app_main.cpp的main函数。3、Android运行时的启动分析上一节分析了Init进程启动与android运行时的关系，因为对于android运行时的启动来说，它是在Init进程之后，zygote进程启动之后，初始化之前初始化的，所以此时它的入口和zygote的入口一致，即app_main.cpp的main函数，代码如下：/app_main.cppint main(int argc, char* const argv) . /AppRuntime继承自AndroidRuntime AppRuntime runtime(argv0, computeArgBlockSize(argc, argv); . if (zygote) /如果init.rc配置中有-Zygote，参数为ernal.os.ZygoteInit runtime.start(ernal.os.ZygoteInit, args); else if (className) /否则参数为ernal.os.RuntimeInit runtime.start(ernal.os.RuntimeInit, args); else /显示命令的用法说明 app_usage(); .首先创建一个AppRuntime对象，接着调用它的start方法，而此start方法在父类AndroidRuntime中进行了定义，并且此处的参数为ernal.os.ZygoteInit，而对于两种不同的参数而言，只是最后启动的类不一样，如果有zygote参数，其最后会启动ZygoteInit类，否则就会执行RuntimeInit类，继续追踪start方法。/AndroidRuntime.cppvoid AndroidRuntime:start(const char* className, const Vector& options) . /启动虚拟机 if (startVm(&mJavaVM, &env) != 0) return; /模板方法模式，只是为了创建VM之后释放slashClassName的内存 onVmCreated(env); /注册Android JNI函数 if (startReg(env) FindClass(slashClassName); if (startClass = NULL) ALOGE(JavaVM unable to locate class %sn, slashClassName); else /得到指定类中指定方法的ID，这里得到的是RuntimeInit.main()的方法ID jmethodID startMeth = env-GetStaticMethodID(startClass, main, (Ljava/lang/String;)V); if (startMeth = NULL) ALOGE(JavaVM unable to find main() in %sn, className); else /调用上面得到的方法ID和相关参数，即调用Java类ZygoteInit.main(); env-CallStaticVoidMethod(startClass, startMeth, strArray); . .首先分析Java虚拟机的启动：由以上代码可知，在start方法中，调用startVm()方法进行虚拟机的启动，startVm()的具体代码如下：/AndroidRuntime.cppint AndroidRuntime:startVm(JavaVM* pJavaVM, JNIEnv* pEnv, bool zygote) . /读取第一个参数指定的属性操作到buffer，并设置默认的参数 parseRuntimeOption(dalvik.vm.stack-trace-file, stackTraceFileBuf, -Xstacktracefile:); . /添加相应的handler操作 addOption(exit, (void*) runtime_exit); . /读取作为dex2oat compiler运行时操作 parseCompilerOption(dex2oat_isa_variant_key, dex2oat_isa_variant, -instruction-set-variant=, -Xcompiler-option); / 拷贝特性 sprintf(dex2oat_isa_features_key, dalvik.vm.isa.%s.features, instruction_set); parseCompilerOption(dex2oat_isa_features_key, dex2oat_isa_features, -instruction-set-features=, -Ximage-compiler-option); parseCompilerOption(dex2oat_isa_features_key, dex2oat_isa_features, -instruction-set-features=, -Xcompiler-option); . /初始化虚拟机 if (JNI_CreateJavaVM(pJavaVM, pEnv, &initArgs) 0) ALOGE(JNI_CreateJavaVM failedn); return -1; .由代码可知：首先进行一系列的属性读取到buffer的操作，如JIT相关的options,DexClassLoader的相关options等，并将其添加到操作数组容器里面，最后再调用JNI_CreateJavaVM方法进行VM的创建,如果此调用发挥成功的话，那么我们就能够济宁JNI调用了，继续看此方法的代码，它的定义出现在DdmConnection的start方法里：/DdmConnection.cppvoid DdmConnection:start(const char* name) . /定义JNI_CreateJavaVM方法 jint (*JNI_CreateJavaVM)(JavaVM* p_vm, JNIEnv* p_env, void* vm_args); /从libart_dso库中解析JNI_CreateJavaVM方法 JNI_CreateJavaVM = reinterpret_cast( dlsym(libart_dso, JNI_CreateJavaVM); /定义registerNatives方法 jint (*registerNatives)(JNIEnv* env, jclass clazz); /从libandroid_runtime_dso库中解析registerNatives方法 registerNatives = reinterpret_cast( dlsym(libandroid_runtime_dso, Java_com_android_internal_util_WithFramework_registerNatives); .JNI_CreateJavaVM方法是从libart_dso库中解析得到的，同样后面要用到的registerNatives方法从事libandroid_runtime_dso库中解析得到的，而这两个库也是在DdmConnection的start方法中打开的，代码如下：void* libart_dso = dlopen(libart.so, RTLD_NOW);ALOGE_IF(!libart_dso, DdmConnection: %s, dlerror();void* libandroid_runtime_dso = dlopen(libandroid_runtime.so, RTLD_NOW);ALOGE_IF(!libandroid_runtime_dso, DdmConnection: %s, dlerror();而当JNI_CreateJavaVM函数执行成功后，当前本地线程已经把自己的控制权交给JVM，而具体的JNI_CreateJavaVM方法的实现在libart_dso库中，此处不做深究。至此，成功创建了Java虚拟机，而startVm方法也分析结束。接着分析onVmCreated方法，它使用的是模板方法的设计模式，在androidRuntime中声明并使用，而具体的实现在appRuntime子类中进行，其代码如下：virtual void onVmCreated(JNIEnv* env) if(mClassName.isEmpty() return;/Zygote.Nothing to do here char* slashClassName = toSlashClassName(mClassName.string(); mClass = env-FndClass(slashClassName); if(mClass = NULL) ALOGE(ERROR:could not find class %sn,mClassName.string); free(slashClassName); mClass = reinterpret(env-NewGlobalRef(mClass);只是简单根据类名获取了类，并释放了类名，所以此处不做过多的分析，接下来分析startReg()方法，方法定义代码如下：/*static*/ int AndroidRuntime:startReg(JNIEnv* env) /* * This hook causes all future threads created in this process to be * attached to the JavaVM. (This needs to go away in favor of JNI * Attach s.) */ androidSetCreateThreadFunc(android_create_thread_fn) javaCreateThreadEtc); ALOGV(- registering native functions -n); /* * Every register function calls one or more things that return * a local reference (e.g. FindClass). Because we havent really * started the VM yet, theyre all g stored in the base frame * and never released. Use Push/Pop to manage the storage. */ env-PushLocalFrame(200); if (register_jni_procs(gRegJNI, NELEM(gRegJNI), env) PopLocalFrame(NULL); return -1; env-PopLocalFrame(NULL); .startReg方法主要的作用是进行android JNI函数的注册，从代码可知：它调用函数register_jni_procs()方法将gRegJNI中的方法注册到虚拟机，而gRegJNI中的Native方法如下：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), 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、非zygote模式的RuntimeInit分析非zygote模式下，app_process命令行的输入参数没有了zygote等，所以className变成了ernal.os.RuntimeInit，但是前面的流程