Dalvik虚拟机的启动过程
文章出处：http://blog.csdn.net/shift_wwx Zygote进程在启动的过程中，除了会创建一个Dalvik虚拟机实例之外，还会将Java运行时库加载到进程中来，以及注册一些Android核心类的JNI方法来前面创建的Dalvik虚拟机实例中去。注意，一个应用程序进程被Zygote进程孵化出来的时候，不仅会获得Zygote进程中的Dalvik虚拟机实例拷贝，还会与
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文章出处：http://blog.csdn.net/shift_wwx
Zygote进程在启动的过程中，除了会创建一个Dalvik虚拟机实例之外，还会将Java运行时库加载到进程中来，以及注册一些Android核心类的JNI方法来前面创建的Dalvik虚拟机实例中去。注意，一个应用程序进程被Zygote进程孵化出来的时候，不仅会获得Zygote进程中的Dalvik虚拟机实例拷贝，还会与Zygote一起共享Java运行时库，这完全得益于Linux内核的进程创建机制（fork）。这种Zygote孵化机制的优点是不仅可以快速地启动一个应用程序进程，还可以节省整体的内存消耗，缺点是会影响开机速度，毕竟Zygote是在开机过程中启动的。不过，总体来说，是利大于弊的，毕竟整个系统只有一个Zygote进程，而可能有无数个应用程序进程，而且我们不会经常去关闭手机，大多数情况下只是让它进入休眠状态。
在启动zygote（android zygote之启动过程分析 ）的时候，会创建虚拟机，做个详细的记录。
@/frameworks/base/cmds/app_process/app_main.cpp
int main(int argc, char* const argv[])
{
#ifdef __arm__
/*
* b/7188322 - Temporarily revert to the compat memory layout
* to avoid breaking third party apps.
*
* THIS WILL GO AWAY IN A FUTURE ANDROID RELEASE.
*
* http://git.kernel.org/?p=linux/kernel/git/torvalds/linux-2.6.git;a=commitdiff;h=7dbaa466
* changes the kernel mapping from bottom up to top-down.
* This breaks some programs which improperly embed
* an out of date copy of Android's linker.
*/
char value[PROPERTY_VALUE_MAX];
property_get("ro.kernel.qemu", value, "");
bool is_qemu = (strcmp(value, "1") == 0);
if ((getenv("NO_ADDR_COMPAT_LAYOUT_FIXUP") == NULL) && !is_qemu) {
int current = personality(0xFFFFFFFF);
if ((current & ADDR_COMPAT_LAYOUT) == 0) {
personality(current | ADDR_COMPAT_LAYOUT);
setenv("NO_ADDR_COMPAT_LAYOUT_FIXUP", "1", 1);
execv("/system/bin/app_process", argv);
return -1;
}
}
unsetenv("NO_ADDR_COMPAT_LAYOUT_FIXUP");
#endif
// These are global variables in ProcessState.cpp
mArgC = argc;
mArgV = argv;
mArgLen = 0;
for (int i=0; i<argc; i++) {
mArgLen += strlen(argv[i]) + 1;
}
mArgLen--;
AppRuntime runtime;
const char* argv0 = argv[0];
// Process command line arguments
// ignore argv[0]
argc--;
argv++;
// Everything up to '--' or first non '-' arg goes to the vm
int i = runtime.addVmArguments(argc, argv);
// Parse runtime arguments. Stop at first unrecognized option.
bool zygote = false;
bool startSystemServer = false;
bool application = false;
const char* parentDir = NULL;
const char* niceName = NULL;
const char* className = NULL;
// YUNOS CODEBASE BEGIN 2014-03-14 peisi.cps@alibaba-inc.com
char system_server_firstboot[PROPERTY_VALUE_MAX];
// YUNOS CODEBASE END
while (i < argc) {
const char* arg = argv[i++];
if (!parentDir) {
parentDir = arg;
} else if (strcmp(arg, "--zygote") == 0) {
zygote = true;
niceName = "zygote";
} else if (strcmp(arg, "--start-system-server") == 0) {
// YUNOS CODEBASE BEGIN 2014-03-14 peisi.cps@alibaba-inc.com
property_get("sys.systemserver.firstboot", system_server_firstboot, "0");
if (strcmp(system_server_firstboot, "1") == 0) {
ALOGE(">>>>>>>>>>>>>>>>>>>>>ANDROID DIED---REBOOT KERNEL<<<<<<<<<<<<<<<<<<<<<<<<<\n");
sync();
usleep(3000*1000L);
__reboot(LINUX_REBOOT_MAGIC1, LINUX_REBOOT_MAGIC2,
LINUX_REBOOT_CMD_RESTART2, (void*)"ANDROID");
} else {
property_set("sys.systemserver.firstboot", "1");
}
// YUNOS CODEBASE END
startSystemServer = true;
} else if (strcmp(arg, "--application") == 0) {
application = true;
} else if (strncmp(arg, "--nice-name=", 12) == 0) {
niceName = arg + 12;
} else {
className = arg;
break;
}
}
if (niceName && *niceName) {
setArgv0(argv0, niceName);
set_process_name(niceName);
}
runtime.mParentDir = parentDir;
if (zygote) {
runtime.start("com.android.internal.os.ZygoteInit",
startSystemServer ? "start-system-server" : "");
} else if (className) {
// Remainder of args get passed to startup class main()
runtime.mClassName = className;
runtime.mArgC = argc - i;
runtime.mArgV = argv + i;
runtime.start("com.android.internal.os.RuntimeInit",
application ? "application" : "tool");
} 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;
}
}
1）变量runtime
AppRuntime runtime;class AppRuntime : public AndroidRuntime
{
public:
AppRuntime()
: mParentDir(NULL)
, mClassName(NULL)
, mClass(NULL)
, mArgC(0)
, mArgV(NULL)
{
}
...
...
const char* getClassName() const
{
return mClassName;
}
virtual void onVmCreated(JNIEnv* env)
{
if (mClassName == NULL) {
return; // Zygote. Nothing to do here.
}
/*
* This is a little awkward because the JNI FindClass call uses the
* class loader associated with the native method we're executing in.
* If called in onStarted (from RuntimeInit.finishInit because we're
* launching "am", for example), FindClass would see that we're calling
* from a boot class' native method, and so wouldn't look for the class
* we're trying to look up in CLASSPATH. Unfortunately it needs to,
* because the "am" classes are not boot classes.
*
* The easiest fix is to call FindClass here, early on before we start
* executing boot class Java code and thereby deny ourselves access to
* non-boot classes.
*/
char* slashClassName = toSlashClassName(mClassName);
mClass = env->FindClass(slashClassName);
if (mClass == NULL) {
ALOGE("ERROR: could not find class '%s'\n", mClassName);
}
free(slashClassName);
mClass = reinterpret_cast<jclass>(env->NewGlobalRef(mClass));
}
virtual void onStarted()
{
sp<ProcessState> proc = ProcessState::self();
ALOGV("App process: starting thread pool.\n");
proc->startThreadPool();
AndroidRuntime* ar = AndroidRuntime::getRuntime();
ar->callMain(mClassName, mClass, mArgC, mArgV);
IPCThreadState::self()->stopProcess();
}
virtual void onZygoteInit()
{
// Re-enable tracing now that we're no longer in Zygote.
atrace_set_tracing_enabled(true);
sp<ProcessState> proc = ProcessState::self();
ALOGV("App process: starting thread pool.\n");
proc->startThreadPool();
}
virtual void onExit(int code)
{
if (mClassName == NULL) {
// if zygote
IPCThreadState::self()->stopProcess();
}
AndroidRuntime::onExit(code);
}
const char* mParentDir;
const char* mClassName;
jclass mClass;
int mArgC;
const char* const* mArgV;
};2）runtime.start
if (zygote) {
runtime.start("com.android.internal.os.ZygoteInit",
startSystemServer ? "start-system-server" : "");
@/frameworks/vase/core/jni/AndroidRuntime.cpp
/*
* Start the Android runtime. This involves starting the virtual machine
* and calling the "static void main(String[] args)" method in the class
* named by "className".
*
* Passes the main function two arguments, the class name and the specified
* options string.
*/
void AndroidRuntime::start(const char* className, const char* options)
{
ALOGD("\n>>>>>> AndroidRuntime START %s <<<<<<\n",
className != NULL ? className : "(unknown)");
/*
* 'startSystemServer == true' means runtime is obsolete and not run from
* init.rc anymore, so we print out the boot start event here.
*/
if (strcmp(options, "start-system-server") == 0) {
/* track our progress through the boot sequence */
const int LOG_BOOT_PROGRESS_START = 3000;
LOG_EVENT_LONG(LOG_BOOT_PROGRESS_START,
ns2ms(systemTime(SYSTEM_TIME_MONOTONIC)));
}
const char* rootDir = getenv("ANDROID_ROOT");
if (rootDir == NULL) {
rootDir = "/system";
if (!hasDir("/system")) {
LOG_FATAL("No root directory specified, and /android does not exist.");
return;
}
setenv("ANDROID_ROOT", rootDir, 1);
}
//const char* kernelHack = getenv("LD_ASSUME_KERNEL");
//ALOGD("Found LD_ASSUME_KERNEL='%s'\n", kernelHack);
/* start the virtual machine */
JniInvocation jni_invocation;
jni_invocation.Init(NULL);
JNIEnv* env;
if (startVm(&mJavaVM, &env) != 0) {
return;
}
onVmCreated(env);
/*
* Register android functions.
*/
if (startReg(env) < 0) {
ALOGE("Unable to register all android natives\n");
return;
}
/*
* We want to call main() with a String array with arguments in it.
* At present we have two arguments, the class name and an option string.
* Create an array to hold them.
*/
jclass stringClass;
jobjectArray strArray;
jstring classNameStr;
jstring optionsStr;
stringClass = env->FindClass("java/lang/String");
assert(stringClass != NULL);
strArray = env->NewObjectArray(2, stringClass, NULL);
assert(strArray != NULL);
classNameStr = env->NewStringUTF(className);
assert(classNameStr != NULL);
env->SetObjectArrayElement(strArray, 0, classNameStr);
optionsStr = env->NewStringUTF(options);
env->SetObjectArrayElement(strArray, 1, optionsStr);
/*
* Start VM. This thread becomes the main thread of the VM, and will
* not return until the VM exits.
*/
char* slashClassName = toSlashClassName(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 {
env->CallStaticVoidMethod(startClass, startMeth, strArray);
#if 0
if (env->ExceptionCheck())
threadExitUncaughtException(env);
#endif
}
}
free(slashClassName);
ALOGD("Shutting down VM\n");
if (mJavaVM->DetachCurrentThread() != JNI_OK)
ALOGW("Warning: unable to detach main thread\n");
if (mJavaVM->DestroyJavaVM() != 0)
ALOGW("Warning: VM did not shut down cleanly\n");
}1）刚开始会打印>>>>>> AndroidRuntime START %s <<<<<<，这里的%s就是zygote，所以logcat的时候都会看到这句话，说明这个时候已经开始启动zygote
2）判断第一次启动的时候options会等于start-system-server
3）设置android_root路径为/system
4）创建虚拟机
/* start the virtual machine */
JniInvocation jni_invocation;
jni_invocation.Init(NULL);
JNIEnv* env;
if (startVm(&mJavaVM, &env) != 0) {
return;
}
onVmCreated(env);JniInvocation::JniInvocation() :
handle_(NULL),
JNI_GetDefaultJavaVMInitArgs_(NULL),
JNI_CreateJavaVM_(NULL),
JNI_GetCreatedJavaVMs_(NULL) {
LOG_ALWAYS_FATAL_IF(jni_invocation_ != NULL, "JniInvocation instance already initialized");
jni_invocation_ = this;
}
JniInvocation::~JniInvocation() {
jni_invocation_ = NULL;
if (handle_ != NULL) {
dlclose(handle_);
}
}
bool JniInvocation::Init(const char* library) {
#ifdef HAVE_ANDROID_OS
char default_library[PROPERTY_VALUE_MAX];
property_get(kLibrarySystemProperty, default_library, kLibraryFallback);
#else
const char* default_library = kLibraryFallback;
#endif
if (library == NULL) {
library = default_library;
}
handle_ = dlopen(library, RTLD_NOW);
if (handle_ == NULL) {
if (strcmp(library, kLibraryFallback) == 0) {
// Nothing else to try.
ALOGE("Failed to dlopen %s: %s", library, dlerror());
return false;
}
// Note that this is enough to get something like the zygote
// running, we can't property_set here to fix this for the future
// because we are root and not the system user. See
// RuntimeInit.commonInit for where we fix up the property to
// avoid future fallbacks. http://b/11463182
ALOGW("Falling back from %s to %s after dlopen error: %s",
library, kLibraryFallback, dlerror());
library = kLibraryFallback;
handle_ = dlopen(library, RTLD_NOW);
if (handle_ == NULL) {
ALOGE("Failed to dlopen %s: %s", library, dlerror());
return false;
}
}
if (!FindSymbol(reinterpret_cast<void**>(&JNI_GetDefaultJavaVMInitArgs_),
"JNI_GetDefaultJavaVMInitArgs")) {
return false;
}
if (!FindSymbol(reinterpret_cast<void**>(&JNI_CreateJavaVM_),
"JNI_CreateJavaVM")) {
return false;
}
if (!FindSymbol(reinterpret_cast<void**>(&JNI_GetCreatedJavaVMs_),
"JNI_GetCreatedJavaVMs")) {
return false;
}
return true;
}当然这里是libdvm.so
startVm函数不做过多的解释，需要注意的是：
char stackTraceFileBuf[PROPERTY_VALUE_MAX];
char dexoptFlagsBuf[PROPERTY_VALUE_MAX];
char enableAssertBuf[sizeof("-ea:")-1 + 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 heaptargetutilizationOptsBuf[sizeof("-XX:HeapTargetUtilization=")-1 + PROPERTY_VALUE_MAX];
char jitcodecachesizeOptsBuf[sizeof("-Xjitcodecachesize:")-1 + PROPERTY_VALUE_MAX];
char extraOptsBuf[PROPERTY_VALUE_MAX];字符串的长度都做了一个PROPERTY_VALUE_MAX的限制。
看一下这个宏定义的地方就知道了：
@system/core/include/cutils/properties.h/* System properties are *small* name value pairs managed by the
** property service. If your data doesn't fit in the provided
** space it is not appropriate for a system property.
**
** WARNING: system/bionic/include/sys/system_properties.h also defines
** these, but with different names. (TODO: fix that)
*/
#define PROPERTY_KEY_MAX PROP_NAME_MAX
#define PROPERTY_VALUE_MAX PROP_VALUE_MAX@/bionic/include/sys/system_properties.h
#define PROP_NAME_MAX 32
#define PROP_VALUE_MAX 92通过串口getprop | grep dalvik
[dalvik.vm.heapgrowthlimit]: [64m]
[dalvik.vm.heapmaxfree]: [8m]
[dalvik.vm.heapminfree]: [512k]
[dalvik.vm.heapsize]: [384m]
[dalvik.vm.heapstartsize]: [8m]
[dalvik.vm.heaptargetutilization]: [0.75]
[dalvik.vm.stack-trace-file]: [/data/anr/traces.txt]
[persist.sys.dalvik.vm.lib]: [libdvm.so] /*
* Initialize the VM.
*
* The JavaVM* is essentially per-process, and the JNIEnv* is per-thread.
* If this call succeeds, the VM is ready, and we can start issuing
* JNI calls.
*/
if (JNI_CreateJavaVM(pJavaVM, pEnv, &initArgs) < 0) {
ALOGE("JNI_CreateJavaVM failed\n");
goto bail;
} JNI_CreateJavaVM主要完成以下四件事情。
1. 为当前进程创建一个Dalvik虚拟机实例，即一个JavaVMExt对象。
2. 为当前线程创建和初始化一个JNI环境，即一个JNIEnvExt对象，这是通过调用函数dvmCreateJNIEnv来完成的。
3. 将参数vm_args所描述的Dalvik虚拟机启动选项拷贝到变量argv所描述的一个字符串数组中去，并且调用函数dvmStartup来初始化前面所创建的Dalvik虚拟机实例。
4. 调用函数dvmChangeStatus将当前线程的状态设置为正在执行NATIVE代码，并且将面所创建和初始化好的JavaVMExt对象和JNIEnvExt对象通过输出参数p_vm和p_env返回给调用者。
gDvm是一个类型为DvmGlobals的全局变量，用来收集当前进程所有虚拟机相关的信息，其中，它的成员变量vmList指向的就是当前进程中的Dalvik虚拟机实例，即一个JavaVMExt对象。以后每当需要访问当前进程中的Dalvik虚拟机实例时，就可以通过全局变量gDvm的成员变量vmList来获得，避免了在函数之间传递该Dalvik虚拟机实例。
每一个Dalvik虚拟机实例都有一个函数表，保存在对应的JavaVMExt对象的成员变量funcTable中，而这个函数表又被指定为gInvokeInterface。gInvokeInterface是一个类型为JNIInvokeInterface的结构体，它定义在文件dalvik/vm/Jni.c中，如下所示：
static const struct JNIInvokeInterface gInvokeInterface = {
NULL,
NULL,
NULL,
DestroyJavaVM,
AttachCurrentThread,
DetachCurrentThread,
GetEnv,
AttachCurrentThreadAsDaemon,
};
具体的可以参考 Dalvik虚拟机启动过程分析，讲的特别详细。
5）注册Android核心类的JNI方法
/*
* Register android functions.
*/
if (startReg(env) < 0) {
ALOGE("Unable to register all android natives\n");
return;
}/*
* Register android native functions with the VM.
*/
/*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 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;
}AndroidRuntime类的成员函数startReg接着调用函数register_jni_procs来注册Android核心类的JNI方法。在注册JNI方法的过程中，需要在Native代码中引用到一些Java对象，这些Java对象引用需要记录在当前线程的一个Native堆栈中。但是此时Dalvik虚拟机还没有真正运行起来，也就是当前线程的Native堆栈还没有准备就绪。在这种情况下，就需要在注册JNI方法之前，手动地将在当前线程的Native堆栈中压入一个帧（Frame），并且在注册JNI方法之后，手动地将该帧弹出来。
当前线程的JNI环境是由参数env所指向的一个JNIEnv对象来描述的，通过调用它的成员函数PushLocalFrame和PopLocalFrame就可以手动地往当前线程的Native堆栈压入和弹出一个帧。注意，这个帧是一个本地帧，只可以用来保存Java对象在Native代码中的本地引用
函数register_jni_procs如下：
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;
}通过观察全局变量gRegJNI所描述的JNI方法注册函数表，我们就可以看出注册了哪些Android核心类的JNI方法，如下所示：
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_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_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_view_DisplayEventReceiver),
REG_JNI(register_android_nio_utils),
REG_JNI(register_android_graphics_Graphics),
REG_JNI(register_android_view_GraphicBuffer),
REG_JNI(register_android_view_GLES20DisplayList),
REG_JNI(register_android_view_GLES20Canvas),
REG_JNI(register_android_view_HardwareRenderer),
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_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_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_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_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_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_net_ethernet_EthernetManager),
REG_JNI(register_android_net_pppoe_PppoeManager),
REG_JNI(register_android_net_wifi_WifiNative),
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_camera2_CameraMetadata),
REG_JNI(register_android_hardware_SensorManager),
REG_JNI(register_android_hardware_SerialPort),
REG_JNI(register_android_hardware_UsbDevice),
REG_JNI(register_android_hardware_UsbDeviceConnection),
REG_JNI(register_android_hardware_UsbRequest),
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_server_Watchdog),
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),
};6）启动zygote main函数
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 {
env->CallStaticVoidMethod(startClass, startMeth, strArray);
总结：
我们就分析完成Dalvik虚拟机在Zygote进程中的启动过程，这个启动过程主要就是完成了以下四个事情：
1. 创建了一个Dalvik虚拟机实例；
2. 加载了Java核心类及其JNI方法；
3. 为主线程的设置了一个JNI环境；
4. 注册了Android核心类的JNI方法。
换句话说，就是Zygote进程为Android系统准备好了一个Dalvik虚拟机实例，以后Zygote进程在创建Android应用程序进程的时候，就可以将它自身的Dalvik虚拟机实例复制到新创建Android应用程序进程中去，从而加快了Android应用程序进程的启动过程。此外，Java核心类和Android核心类（位于dex文件中），以及它们的JNI方法（位于so文件中），都是以内存映射的方式来读取的，因此，Zygote进程在创建Android应用程序进程的时候，除了可以将自身的Dalvik虚拟机实例复制到新创建的Android应用程序进程之外，还可以与新创建的Android应用程序进程共享Java核心类和Android核心类，以及它们的JNI方法，这样就可以节省内存消耗。
同时，我们也应该看到，Zygote进程为了加快Android应用程序进程的启动过程，牺牲了自己的启动速度，因为它需要加载大量的Java核心类，以及注册大量的Android核心类JNI方法。Dalvik虚拟机在加载Java核心类的时候，还需要对它们进行验证以及优化，这些通常都是比较耗时的。又由于Zygote进程是由init进程启动的，也就是说Zygote进程在是开机的时候进行启动的，因此，Zygote进程的牺牲是比较大的。不过毕竟我们在玩手机的时候，很少会关机，也就是很少开机，因此，牺牲Zygote进程的启动速度是值得的，换来的是Android应用程序的快速启动。而且，Android系统为了加快Java类的加载速度，还会想方设法地提前对Dex文件进行验证和优化，这些措施具体参考Dalvik Optimization and Verification With dexopt一文。
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