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在使用app_process 创建zygote进程的过程中会执行下面这些操作:
  • 创建ART虚拟机
  • 注册Native方法
  • 找到ZygoteInit,通过反射调用它的main方法进入Java世界
这里说一下注册Native方法的一些细节.

入口

/* * Register android functions. */ if (startReg(env) < 0) { ALOGE("Unable to register all android natives\\n"); return; }
源码在frameworks/base/core/jni/AndroidRuntime.cpp中.
/* * Register android native functions with the VM. */ /*static*/ int AndroidRuntime::startReg(JNIEnv* env) { ATRACE_NAME("RegisterAndroidNatives"); /* * 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 calls.) */ 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 haven't really * started the VM yet, they're all getting 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) < 0) { env->PopLocalFrame(NULL); return -1; } env->PopLocalFrame(NULL); //createJavaThread("fubar", quickTest, (void*) "hello"); return 0; }

要注册的方法

static const RegJNIRec gRegJNI[] = { REG_JNI(register_com_android_internal_os_RuntimeInit), REG_JNI(register_com_android_internal_os_ZygoteInit_nativeZygoteInit), REG_JNI(register_android_os_SystemClock), REG_JNI(register_android_util_EventLog), REG_JNI(register_android_util_Log), REG_JNI(register_android_util_MemoryIntArray), REG_JNI(register_android_util_PathParser), REG_JNI(register_android_util_StatsLog), REG_JNI(register_android_util_StatsLogInternal), REG_JNI(register_android_app_admin_SecurityLog), REG_JNI(register_android_content_AssetManager), REG_JNI(register_android_content_StringBlock), REG_JNI(register_android_content_XmlBlock), REG_JNI(register_android_content_res_ApkAssets), REG_JNI(register_android_text_AndroidCharacter), REG_JNI(register_android_text_Hyphenator), 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_os_HidlMemory), REG_JNI(register_android_os_HidlSupport), REG_JNI(register_android_os_HwBinder), REG_JNI(register_android_os_HwBlob), REG_JNI(register_android_os_HwParcel), REG_JNI(register_android_os_HwRemoteBinder), REG_JNI(register_android_os_NativeHandle), REG_JNI(register_android_os_VintfObject), REG_JNI(register_android_os_VintfRuntimeInfo), REG_JNI(register_android_graphics_Canvas), // This needs to be before register_android_graphics_Graphics, or the latter // will not be able to find the jmethodID for ColorSpace.get(). REG_JNI(register_android_graphics_ColorSpace), 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_DisplayListCanvas), REG_JNI(register_android_view_InputApplicationHandle), REG_JNI(register_android_view_InputWindowHandle), REG_JNI(register_android_view_TextureLayer), 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_CompositionSamplingListener), 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_EGL15), 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_opengl_jni_GLES32), REG_JNI(register_android_graphics_Bitmap), REG_JNI(register_android_graphics_BitmapFactory), REG_JNI(register_android_graphics_BitmapRegionDecoder), REG_JNI(register_android_graphics_ByteBufferStreamAdaptor), REG_JNI(register_android_graphics_Camera), REG_JNI(register_android_graphics_CreateJavaOutputStreamAdaptor), 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_GraphicBuffer), REG_JNI(register_android_graphics_ImageDecoder), REG_JNI(register_android_graphics_drawable_AnimatedImageDrawable), REG_JNI(register_android_graphics_Interpolator), 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_Region), REG_JNI(register_android_graphics_Shader), REG_JNI(register_android_graphics_SurfaceTexture), REG_JNI(register_android_graphics_Typeface), REG_JNI(register_android_graphics_YuvImage), REG_JNI(register_android_graphics_drawable_AnimatedVectorDrawable), REG_JNI(register_android_graphics_drawable_VectorDrawable), REG_JNI(register_android_graphics_fonts_Font), REG_JNI(register_android_graphics_fonts_FontFamily), 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_graphics_text_MeasuredText), REG_JNI(register_android_graphics_text_LineBreaker), 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_GraphicsEnvironment), 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_os_MemoryFile), REG_JNI(register_android_os_SharedMemory), REG_JNI(register_com_android_internal_os_ClassLoaderFactory), REG_JNI(register_com_android_internal_os_Zygote), REG_JNI(register_com_android_internal_os_ZygoteInit), 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_HardwareBuffer), 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_AudioEffectDescriptor), REG_JNI(register_android_media_AudioSystem), REG_JNI(register_android_media_AudioRecord), REG_JNI(register_android_media_AudioTrack), REG_JNI(register_android_media_AudioAttributes), REG_JNI(register_android_media_AudioProductStrategies), REG_JNI(register_android_media_AudioVolumeGroups), REG_JNI(register_android_media_AudioVolumeGroupChangeHandler), REG_JNI(register_android_media_MicrophoneInfo), REG_JNI(register_android_media_RemoteDisplay), REG_JNI(register_android_media_ToneGenerator), REG_JNI(register_android_media_midi), 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_Activity), REG_JNI(register_android_app_ActivityThread), REG_JNI(register_android_app_NativeActivity), REG_JNI(register_android_util_jar_StrictJarFile), 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_android_security_Scrypt), REG_JNI(register_com_android_internal_content_NativeLibraryHelper), REG_JNI(register_com_android_internal_os_AtomicDirectory), REG_JNI(register_com_android_internal_os_FuseAppLoop), REG_JNI(register_com_android_internal_os_KernelCpuUidBpfMapReader), REG_JNI(register_com_android_internal_os_KernelSingleUidTimeReader), };
其中register_xx其实是一个函数指针,遍历的时候会依次执行这些方法:
static int register_jni_procs(const RegJNIRec array[], size_t count, JNIEnv* env) { for (size_t i = 0; i < count; i++) { if (array[i].mProc(env) < 0) { #ifndef NDEBUG ALOGD("----------!!! %s failed to load\\n", array[i].mName); #endif return -1; } } return 0; }
int register_com_android_internal_os_RuntimeInit(JNIEnv* env) { const JNINativeMethod methods[] = { {"nativeFinishInit", "()V", (void*)com_android_internal_os_RuntimeInit_nativeFinishInit}, {"nativeSetExitWithoutCleanup", "(Z)V", (void*)com_android_internal_os_RuntimeInit_nativeSetExitWithoutCleanup}, }; return jniRegisterNativeMethods(env, "com/android/internal/os/RuntimeInit", methods, NELEM(methods)); }
可以看到需要传入用到JNI方法的Java类名以及用到的Native方法签名.
实际注册操作都是通过jniRegisterNativeMethods方法:
inline int jniRegisterNativeMethods(JNIEnv* env, const char* className, const JNINativeMethod* gMethods, int numMethods) { return jniRegisterNativeMethods(&env->functions, className, gMethods, numMethods); }
实现在libnativehelper/JNIHelp.c中:
int jniRegisterNativeMethods(JNIEnv* env, const char* className, const JNINativeMethod* methods, int numMethods) { ALOGV("Registering %s's %d native methods...", className, numMethods); jclass clazz = (*env)->FindClass(env, className); ALOG_ALWAYS_FATAL_IF(clazz == NULL, "Native registration unable to find class '%s'; aborting...", className); int result = (*env)->RegisterNatives(env, clazz, methods, numMethods); (*env)->DeleteLocalRef(env, clazz); if (result == 0) { return 0; } // Failure to register natives is fatal. Try to report the corresponding exception, // otherwise abort with generic failure message. jthrowable thrown = (*env)->ExceptionOccurred(env); if (thrown != NULL) { struct ExpandableString summary; ExpandableStringInitialize(&summary); if (GetExceptionSummary(env, thrown, &summary)) { ALOGF("%s", summary.data); } ExpandableStringRelease(&summary); (*env)->DeleteLocalRef(env, thrown); } ALOGF("RegisterNatives failed for '%s'; aborting...", className); return result; }
这些要注册的Native方法实现大部分都在frameworks/base/core/jni下.
我门来看一下Canvas中Native方法的注册:
static const JNINativeMethod gMethods[] = { {"nGetNativeFinalizer", "()J", (void*) CanvasJNI::getNativeFinalizer}, {"nFreeCaches", "()V", (void*) CanvasJNI::freeCaches}, {"nFreeTextLayoutCaches", "()V", (void*) CanvasJNI::freeTextLayoutCaches}, {"nSetCompatibilityVersion", "(I)V", (void*) CanvasJNI::setCompatibilityVersion}, // ------------ @FastNative ---------------- {"nInitRaster", "(J)J", (void*) CanvasJNI::initRaster}, {"nSetBitmap", "(JJ)V", (void*) CanvasJNI::setBitmap}, {"nGetClipBounds","(JLandroid/graphics/Rect;)Z", (void*) CanvasJNI::getClipBounds}, // ------------ @CriticalNative ---------------- {"nIsOpaque","(J)Z", (void*) CanvasJNI::isOpaque}, {"nGetWidth","(J)I", (void*) CanvasJNI::getWidth}, {"nGetHeight","(J)I", (void*) CanvasJNI::getHeight}, {"nSave","(JI)I", (void*) CanvasJNI::save}, {"nSaveLayer","(JFFFFJI)I", (void*) CanvasJNI::saveLayer}, {"nSaveLayerAlpha","(JFFFFII)I", (void*) CanvasJNI::saveLayerAlpha}, {"nSaveUnclippedLayer","(JIIII)I", (void*) CanvasJNI::saveUnclippedLayer}, {"nRestoreUnclippedLayer","(JIJ)V", (void*) CanvasJNI::restoreUnclippedLayer}, {"nGetSaveCount","(J)I", (void*) CanvasJNI::getSaveCount}, {"nRestore","(J)Z", (void*) CanvasJNI::restore}, {"nRestoreToCount","(JI)V", (void*) CanvasJNI::restoreToCount}, {"nGetMatrix", "(JJ)V", (void*)CanvasJNI::getMatrix}, {"nSetMatrix","(JJ)V", (void*) CanvasJNI::setMatrix}, {"nConcat","(JJ)V", (void*) CanvasJNI::concat}, {"nRotate","(JF)V", (void*) CanvasJNI::rotate}, {"nScale","(JFF)V", (void*) CanvasJNI::scale}, {"nSkew","(JFF)V", (void*) CanvasJNI::skew}, {"nTranslate","(JFF)V", (void*) CanvasJNI::translate}, {"nQuickReject","(JJ)Z", (void*) CanvasJNI::quickRejectPath}, {"nQuickReject","(JFFFF)Z", (void*)CanvasJNI::quickRejectRect}, {"nClipRect","(JFFFFI)Z", (void*) CanvasJNI::clipRect}, {"nClipPath","(JJI)Z", (void*) CanvasJNI::clipPath}, {"nSetDrawFilter", "(JJ)V", (void*) CanvasJNI::setPaintFilter}, }; // If called from Canvas these are regular JNI // If called from DisplayListCanvas they are @FastNative static const JNINativeMethod gDrawMethods[] = { {"nDrawColor","(JII)V", (void*) CanvasJNI::drawColor}, {"nDrawColor","(JJJI)V", (void*) CanvasJNI::drawColorLong}, {"nDrawPaint","(JJ)V", (void*) CanvasJNI::drawPaint}, {"nDrawPoint", "(JFFJ)V", (void*) CanvasJNI::drawPoint}, {"nDrawPoints", "(J[FIIJ)V", (void*) CanvasJNI::drawPoints}, {"nDrawLine", "(JFFFFJ)V", (void*) CanvasJNI::drawLine}, {"nDrawLines", "(J[FIIJ)V", (void*) CanvasJNI::drawLines}, {"nDrawRect","(JFFFFJ)V", (void*) CanvasJNI::drawRect}, {"nDrawRegion", "(JJJ)V", (void*) CanvasJNI::drawRegion }, {"nDrawRoundRect","(JFFFFFFJ)V", (void*) CanvasJNI::drawRoundRect}, {"nDrawDoubleRoundRect", "(JFFFFFFFFFFFFJ)V", (void*) CanvasJNI::drawDoubleRoundRectXY}, {"nDrawDoubleRoundRect", "(JFFFF[FFFFF[FJ)V", (void*) CanvasJNI::drawDoubleRoundRectRadii}, {"nDrawCircle","(JFFFJ)V", (void*) CanvasJNI::drawCircle}, {"nDrawOval","(JFFFFJ)V", (void*) CanvasJNI::drawOval}, {"nDrawArc","(JFFFFFFZJ)V", (void*) CanvasJNI::drawArc}, {"nDrawPath","(JJJ)V", (void*) CanvasJNI::drawPath}, {"nDrawVertices", "(JII[FI[FI[II[SIIJ)V", (void*)CanvasJNI::drawVertices}, {"nDrawNinePatch", "(JJJFFFFJII)V", (void*)CanvasJNI::drawNinePatch}, {"nDrawBitmapMatrix", "(JJJJ)V", (void*)CanvasJNI::drawBitmapMatrix}, {"nDrawBitmapMesh", "(JJII[FI[IIJ)V", (void*)CanvasJNI::drawBitmapMesh}, {"nDrawBitmap","(JJFFJIII)V", (void*) CanvasJNI::drawBitmap}, {"nDrawBitmap","(JJFFFFFFFFJII)V", (void*) CanvasJNI::drawBitmapRect}, {"nDrawBitmap", "(J[IIIFFIIZJ)V", (void*)CanvasJNI::drawBitmapArray}, {"nDrawText","(J[CIIFFIJ)V", (void*) CanvasJNI::drawTextChars}, {"nDrawText","(JLjava/lang/String;IIFFIJ)V", (void*) CanvasJNI::drawTextString}, {"nDrawTextRun","(J[CIIIIFFZJJ)V", (void*) CanvasJNI::drawTextRunChars}, {"nDrawTextRun","(JLjava/lang/String;IIIIFFZJ)V", (void*) CanvasJNI::drawTextRunString}, {"nDrawTextOnPath","(J[CIIJFFIJ)V", (void*) CanvasJNI::drawTextOnPathChars}, {"nDrawTextOnPath","(JLjava/lang/String;JFFIJ)V", (void*) CanvasJNI::drawTextOnPathString}, }; int register_android_graphics_Canvas(JNIEnv* env) { int ret = 0; ret |= RegisterMethodsOrDie(env, "android/graphics/Canvas", gMethods, NELEM(gMethods)); ret |= RegisterMethodsOrDie(env, "android/graphics/BaseCanvas", gDrawMethods, NELEM(gDrawMethods)); ret |= RegisterMethodsOrDie(env, "android/graphics/BaseRecordingCanvas", gDrawMethods, NELEM(gDrawMethods)); return ret; }
使用JNIEnv的RegisterNatives方法实际上就是在Java的native方法名与C++中的JNI调用方法签名之间建立一个映射关系,从而避免了在C++中必须写那些丑陋的方法名了.
RegisterNatives的使用在JNI开发中还是非常常见的,比如我们经常会在JNI_Onload方法中注册Native方法,还是会使用到RegisterNatives方法.

总结

  1. 灵活使用ReigsterNatives方法,不一定必须在JNI_OnLoad()方法中调用,也可以自行调用
  1. JNI中绝大部分方法都在JNIEnv中;
Android系统启动流程-SystemServer分析Android系统启动流程-ART虚拟机的启动
姜康
姜康
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