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目录
Android之zygote源码剖析（一）
Android之zygote源码剖析（二）
Android之zygote源码剖析（三）
Android之SystemServer介绍（一）
Android之SystemServer介绍（二）
Android之Launcher介绍（一））
c库zygote源码
上文分析了c库的zygote源码，后续调用runtime.start启动虚拟机并进入JAVA部分。
先来看下runtime.start的代码(AndroidRuntime.h)
……
#include <utils/Errors.h>
#include <binder/IBinder.h>
#include <utils/String8.h>
#include <utils/String16.h>
#include <utils/Vector.h>
#include <utils/threads.h>
#include <pthread.h>
#include <nativehelper/jni.h>
namespace android {
class AndroidRuntime
{
public:
……
/**
* Call a class's static main method with the given arguments,
*/
status_t callMain(const String8& className, jclass clazz, const Vector<String8>& args);
/**
* Find a class, with the input either of the form
* "package/class" or "package.class".
*/
static jclass findClass(JNIEnv* env, const char* className);
void start(const char *classname, const Vector<String8>& options, bool zygote);
void exit(int code);
void setExitWithoutCleanup(bool exitWithoutCleanup) {
mExitWithoutCleanup = exitWithoutCleanup;
}
static AndroidRuntime* getRuntime();
/**
* This gets called after the VM has been created, but before we
* run any code. Override it to make any FindClass calls that need
* to use CLASSPATH.
*/
virtual void onVmCreated(JNIEnv* env);
……
};
}
#endif
void AndroidRuntime::start(const char* className, const Vector<String8>& options, bool zygote)
{
ALOGD(">>>>>> START %s uid %d <<<<<<\n",
className != NULL ? className : "(unknown)", getuid());
static const String8 startSystemServer("start-system-server");
// “startSystemServer==true”表示运行时已过时，不能从init.rc中运行，所以我们在这里打印启动事件。
for (size_t i = 0; i < options.size(); ++i) {
if (options[i] == startSystemServer) {
/* 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)));
}
}
// 根据环境变量，设置目录
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);
}
JniInvocation jni_invocation;
jni_invocation.Init(NULL);
JNIEnv* env;
// 启动虚拟机
if (startVm(&mJavaVM, &env, zygote) != 0) {
return;
}
onVmCreated(env);
// 为java虚拟机注册JNI方法
if (startReg(env) < 0) {
ALOGE("Unable to register all android natives\n");
return;
}
jclass stringClass;
jobjectArray strArray;
jstring classNameStr;
// 调用JNI的方法
stringClass = env->FindClass("java/lang/String");
assert(stringClass != NULL);
strArray = env->NewObjectArray(options.size() + 1, stringClass, NULL);
assert(strArray != NULL);
// className == com.android.internal.os.ZygoteInit
classNameStr = env->NewStringUTF(className);
assert(classNameStr != NULL);
env->SetObjectArrayElement(strArray, 0, classNameStr);
for (size_t i = 0; i < options.size(); ++i) {
jstring optionsStr = env->NewStringUTF(options.itemAt(i).string());
assert(optionsStr != NULL);
env->SetObjectArrayElement(strArray, i + 1, optionsStr);
}
// 将com.android.internal.os.ZygoteInit换成com/android/internal/os/ZygoteInit
char* slashClassName = toSlashClassName(className);
jclass startClass = env->FindClass(slashClassName);
if (startClass == NULL) {
ALOGE("JavaVM unable to locate class '%s'\n", slashClassName);
/* keep going */
} else {
// 找到ZygoteInit类的main方法
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 {
// JNI调用JAVA方法，执行ZygoteInit类的main方法
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");
}
代码中有注释解释。
从上面可以看出之后执行到了ZygoteInit类的main方法(ZygoteInit.java)：
public static void main(String argv[]) {
// 创建一个ZygoteServer
ZygoteServer zygoteServer = new ZygoteServer();
// 启动zygote
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);
}
try {
……
// 注册socker，名字为zygote
zygoteServer.registerServerSocket(socketName);
if (!enableLazyPreload) {
bootTimingsTraceLog.traceBegin("ZygotePreload");
EventLog.writeEvent(LOG_BOOT_PROGRESS_PRELOAD_START,
SystemClock.uptimeMillis());
// 预加载类和资源
preload(bootTimingsTraceLog);
EventLog.writeEvent(LOG_BOOT_PROGRESS_PRELOAD_END,
SystemClock.uptimeMillis());
bootTimingsTraceLog.traceEnd(); // ZygotePreload
} else {
Zygote.resetNicePriority();
}
SamplingProfilerIntegration.writeZygoteSnapshot();
bootTimingsTraceLog.traceBegin("PostZygoteInitGC");
gcAndFinalize();
bootTimingsTraceLog.traceEnd();
bootTimingsTraceLog.traceEnd();
Trace.setTracingEnabled(false);
Zygote.nativeUnmountStorageOnInit();
Seccomp.setPolicy();
ZygoteHooks.stopZygoteNoThreadCreation();
// 启动系统服务
if (startSystemServer) {
startSystemServer(abiList, socketName, zygoteServer);
}
Log.i(TAG, "Accepting command socket connections");
// 执行select，等待AMS发过来创建app请求
zygoteServer.runSelectLoop(abiList);
zygoteServer.closeServerSocket();
} catch (Zygote.MethodAndArgsCaller caller) {
caller.run();
} catch (Throwable ex) {
Log.e(TAG, "System zygote died with exception", ex);
zygoteServer.closeServerSocket();
throw ex;
}
}
大致分为四步：
- 创建zygote服务，并注册socket。
- 预加载类和资源。
- 系统SystemService进程。
- 上面注册的服务等待AMS的请求。
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