Android Zygote系统进程启动过程分析Android N.docx

1、Android Zygote系统进程启动过程分析Android NAndroid Zygote系统进程启动过程分析(Android N) 在Android系统中，所有的应用程序进程以及系统服务进程SystemServer都是由Zygote进程孕育（fork）出来的，因为Android系统是基于Linux内核的，而在Linux系统中，所有的进程都是init进程的子孙进程，也就是说，所有的进程都是直接或者间接地由init进程fork出来的。Zygote进程也不例外，它是在系统启动的过程，由init进程创建的，在系统启动脚本system/core/rootdir/init.rc文件中，我们可以看到启

2、动Zygote进程的脚本命令：cpp view plain copy 在CODE上查看代码片派生到我的代码片import /init.$ro.zygote.rc 从上面的代码可以看出，在system/core/rootdir目录下系统不止一个zygote*.rc文件每个文件里的启动zygote方式差不多，下面就以init.zygote64_32.rc为例看下里面的代码cpp view plain copy 在CODE上查看代码片派生到我的代码片service zygote /system/bin/app_process64 -Xzygote /system/bin -zygote -start

3、-system-server -socket-name=zygote class main socket zygote stream 660 root system onrestart write /sys/android_power/request_state wake onrestart write /sys/power/state on onrestart restart audioserver onrestart restart cameraserver onrestart restart media onrestart restart netd writepid /dev/cpuse

4、t/foreground/tasks service zygote_secondary /system/bin/app_process32 -Xzygote /system/bin -zygote -socket-name=zygote_secondary class main socket zygote_secondary stream 660 root system onrestart restart zygote writepid /dev/cpuset/foreground/tasks 看到上面的代码估计你也能猜出来另外三个zygote*.rc是怎样的，具体选择哪个文件和编译时定义的r

5、o.zygote值有关。前面的关键字service告诉init进程创建一个名为zygote的进程，这个zygote进程要执行的程序是/system/bin/app_process64，后面是要传给app_process64的参数。 接下来的class main表示执行system/bin/app_process64后调用main方法，socket关键字表示这个zygote进程需要一个名称为zygote的socket资源，这样，系统启动后，我们就可以在/dev/socket目录下看到有一个名为zygote的文件，onrestart关键字表示这个zygote进程重启时需要执行的命令，最后一个wri

6、tepid关键字表示需要重写系统pid。 通过上面我们知道Zygote进程要执行的程序便是app_process64了，它位于frameworks/base/cmds/app_process/app_main.cpp文件中，入口函数是main。（app_process64 or app_process32 都是通过frameworks/base/cmds/app_process编译出来的，只是由编译环境来决定生成那个文件），在分析zygote进程启动之前，来看看它启动的时序图下面就看看从app_process64到Zygote启动具体流程：1、在app_main.cpp的main函数中利用An

7、droidRuntime启动Zygotejava view plain copy 在CODE上查看代码片派生到我的代码片int main(int argc, char* const argv) if (prctl(PR_SET_NO_NEW_PRIVS, 1, 0, 0, 0) 0) / Older kernels dont understand PR_SET_NO_NEW_PRIVS and return / EINVAL. Dont die on such kernels. if (errno != EINVAL) LOG_ALWAYS_FATAL(PR_SET_NO_NEW_PRIVS

8、failed: %s, strerror(errno); return 12; AppRuntime runtime(argv0, computeArgBlockSize(argc, argv); / Process command line arguments / ignore argv0 argc-; argv+; / Everything up to - or first non - arg goes to the vm. / / The first argument after the VM args is the parent dir, which / is currently un

9、used. / / After the parent dir, we expect one or more the following internal / arguments : / / -zygote : Start in zygote mode / -start-system-server : Start the system server. / -application : Start in application (stand alone, non zygote) mode. / -nice-name : The nice name for this process. / / For

10、 non zygote starts, these arguments will be followed by / the main class name. All remaining arguments are passed to / the main method of this class. / / For zygote starts, all remaining arguments are passed to the zygote. / main function. / / Note that we must copy argument string values since we w

11、ill rewrite the / entire argument block when we apply the nice name to argv0. int i; for (i = 0; i argc; i+) if (argvi0 != -) break; if (argvi1 = - & argvi2 = 0) +i; / Skip -. break; runtime.addOption(strdup(argvi); / Parse runtime arguments. Stop at first unrecognized option. bool zygote = false; b

12、ool startSystemServer = false; bool application = false; String8 niceName; String8 className; +i; / Skip unused parent dir argument. while (i argc) const char* arg = argvi+; if (strcmp(arg, -zygote) = 0) zygote = true; niceName = ZYGOTE_NICE_NAME; else if (strcmp(arg, -start-system-server) = 0) star

13、tSystemServer = true; else if (strcmp(arg, -application) = 0) application = true; else if (strncmp(arg, -nice-name=, 12) = 0) niceName.setTo(arg + 12); else if (strncmp(arg, -, 2) != 0) className.setTo(arg); break; else -i; break; Vector args; if (!className.isEmpty() / Were not in zygote mode, the

14、only argument we need to pass / to RuntimeInit is the application argument. / / The Remainder of args get passed to startup class main(). Make / copies of them before we overwrite them with the process name. args.add(application ? String8(application) : String8(tool); runtime.setClassNameAndArgs(cla

15、ssName, argc - i, argv + i); else / Were in zygote mode. maybeCreateDalvikCache(); if (startSystemServer) args.add(String8(start-system-server); char propPROP_VALUE_MAX; if (property_get(ABI_LIST_PROPERTY, prop, NULL) = 0) LOG_ALWAYS_FATAL(app_process: Unable to determine ABI list from property %s.,

16、 ABI_LIST_PROPERTY); return 11; String8 abiFlag(-abi-list=); abiFlag.append(prop); args.add(abiFlag); / In zygote mode, pass all remaining arguments to the zygote / main() method. for (; i argc; +i) args.add(String8(argvi); if (!niceName.isEmpty() runtime.setArgv0(niceName.string(); set_process_name

17、(niceName.string(); if (zygote) runtime.start(com.android.internal.os.ZygoteInit, args, zygote);/启动ZygoteInit else if (className) runtime.start(com.android.internal.os.RuntimeInit, args, zygote); else fprintf(stderr, Error: no class name or -zygote supplied.n); app_usage(); LOG_ALWAYS_FATAL(app_proc

18、ess: no class name or -zygote supplied.); return 10; main函数的主要作用就是创建一个AppRuntime变量，然后调用它的start成员函数，AppRuntime这个类同样是在frameworks/base/cmds/app_process/app_main.cpp文件中定义：java view plain copy 在CODE上查看代码片派生到我的代码片class AppRuntime : public AndroidRuntime public: AppRuntime(char* argBlockStart, const size_t

19、 argBlockLength) : AndroidRuntime(argBlockStart, argBlockLength) , mClass(NULL) void setClassNameAndArgs(const String8& className, int argc, char * const *argv) mClassName = className; for (int i = 0; i FindClass(slashClassName); if (mClass = NULL) ALOGE(ERROR: could not find class %sn, mClassName.s

20、tring(); free(slashClassName); mClass = reinterpret_cast(env-NewGlobalRef(mClass); virtual void onStarted() sp proc = ProcessState:self(); ALOGV(App process: starting thread pool.n); proc-startThreadPool(); AndroidRuntime* ar = AndroidRuntime:getRuntime(); ar-callMain(mClassName, mClass, mArgs); IPC

21、ThreadState:self()-stopProcess(); virtual void onZygoteInit() sp proc = ProcessState:self(); ALOGV(App process: starting thread pool.n); proc-startThreadPool(); virtual void onExit(int code) if (mClassName.isEmpty() / if zygote IPCThreadState:self()-stopProcess(); AndroidRuntime:onExit(code); String

22、8 mClassName; Vector mArgs; jclass mClass; ; 回到上面的main函数中，由于我们在init.zygote64_32.rc文件中，设置了app_process启动参数-zygote和-start-system-server，因此，在main函数里面，最终会执行下面语句：java view plain copy 在CODE上查看代码片派生到我的代码片runtime.start(com.android.internal.os.ZygoteInit, args, zygote); args参数，在上面main函数里定义的，从main函数可以看出还需要启动st

23、art-system-server，这个方法的实现具体如下java view plain copy 在CODE上查看代码片派生到我的代码片frameworks/base/core/jni/AndroidRuntime.cpp void AndroidRuntime:start(const char* className, const Vector& options, bool zygote) ALOGD( START %s uid %d n, className != NULL ? className : (unknown), getuid(); static const String8 st

24、artSystemServer(start-system-server); /* * startSystemServer = true means runtime is obsolete and not run from * init.rc anymore, so we print out the boot start event here. */ for (size_t i = 0; i options.size(); +i) if (optionsi = startSystemServer) /* track our progress through the boot sequence *

25、/ 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.); r

26、eturn; setenv(ANDROID_ROOT, rootDir, 1); /const char* kernelHack = getenv(LD_ASSUME_KERNEL); /ALOGD(Found LD_ASSUME_KERNEL=%sn, kernelHack); /* start the virtual machine */ JniInvocation jni_invocation; jni_invocation.Init(NULL); JNIEnv* env; if (startVm(&mJavaVM, &env, zygote) != 0) return; onVmCreated(env); /* * Register android functions. */ if (startReg(env) FindClass(java/lang/String); assert(stringClass != NULL); strArray = env-NewObjectArray(options.size() + 1, stringClass, NULL); assert(strArray != NULL); classNameStr = env-NewStringUTF(className); assert(classNameStr !=