android开机启动流程简单分析

1、android开机启动流程简单分析android启动当引导程序启动Linux内核后，会加载各种驱动和数据结构，当有了驱动以后，开始启动Android系统同时会加载用户级别的第一个进程init（systemcoreinitinit.cpp）代码如下：int main(int argc, char* argv) . /创建文件夹，挂载 / Get the basic filesystem setup we need put together in the initramdisk / on / and then we'll let the rc file figure out the res

2、t. if (is_first_stage) mount("tmpfs", "/dev", "tmpfs", MS_NOSUID, "mode=0755"); mkdir("/dev/pts", 0755); mkdir("/dev/socket", 0755); mount("devpts", "/dev/pts", "devpts", 0, NULL); #define MAKE_STR(x) _STRING(x

3、) mount("proc", "/proc", "proc", 0, "hidepid=2,gid=" MAKE_STR(AID_READPROC); mount("sysfs", "/sys", "sysfs", 0, NULL); . /打印日志，设置log的级别 klog_init(); klog_set_level(KLOG_NOTICE_LEVEL); . Parser& parser = Parser:GetInstance(); p

4、arser.AddSectionParser("service",std:make_unique<ServiceParser>(); parser.AddSectionParser("on", std:make_unique<ActionParser>(); parser.AddSectionParser("import", std:make_unique<ImportParser>(); / 加载init.rc配置文件 parser.ParseConfig("/init.rc"

5、);加载init.rc文件，会启动一个Zygote进程，此进程是Android系统的一个母进程，用来启动Android的其他服务进程，代码：从Android L开始，在 /system/core/rootdir 目录中有 4 个 zygote 相关的启动脚本如下图：在init.rc文件中，有如下代码：import /init.environ.rcimport /init.usb.rcimport /init.$ro.hardware.rcimport /init.usb.configfs.rcimport /init.$ro.zygote.rc注意到上面的代码import /init.$ro.

6、zygote.rc，这里会读取ro.zygote这个属性，导入相应的init.rc文件。 ro.zygote的属性可为：zygote32、zygote64、zygote32_64、zygote64_32。对于这个属性的解释如下。init.zygote32.rc：zygote 进程对应的执行程序是 app_process (纯 32bit 模式)init.zygote64.rc：zygote 进程对应的执行程序是 app_process64 (纯 64bit 模式)init.zygote32_64.rc：启动两个 zygote 进程 (名为 zygote 和 zygote_secondary)，

7、对应的执行程序分别是 app_process32 (主模式)、app_process64。init.zygote64_32.rc：启动两个 zygote 进程 (名为 zygote 和 zygote_secondary)，对应的执行程序分别是 app_process64 (主模式)、app_process32主流的机型属性都为zygote64_32，我们来看看init.zygote64_32.rc文件：service zygote /system/bin/app_process64 -Xzygote /system/bin -zygote -start-system-server -socke

8、t-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/cpuset/foreground/tasksser

9、vice 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在 Linux 系统中，service 通常是一种被称为守护进程 (daemon) 的程序。它通常在系统启动时启动，并一直运行于后台，直到系统关闭

10、时终止。这里会以service方式来启动zygote进程，app_process的代码位于/frameworks/base/cmds/app_process/路径下，该路径下有一个文件app_main.cpp,入口是main函数。接下来看app_main.cpp函数，这里实现从c+代码调到java代码：int main(int argc, char* const argv) . /android运行时环境 AppRuntime runtime(argv0, computeArgBlockSize(argc, argv); / Process command line arguments / i

11、gnore argv0 argc-; argv+; . if (zygote) /启动java代码 runtime.start("ernal.os.ZygoteInit", args, zygote); else if (className) runtime.start("ernal.os.RuntimeInit", args, zygote); else fprintf(stderr, "Error: no class name or -zygote supplied.n"

12、); app_usage(); LOG_ALWAYS_FATAL("app_process: no class name or -zygote supplied."); return 10; ZygoteInit.java 代码：/frameworks/base/core/Java/com/android/internal/os/ZygoteInit.java public static void main(String argv) . try . boolean startSystemServer = false; String socketName = "zy

13、gote" String abiList = null; for (int i = 1; i < argv.length; i+) if ("start-system-server".equals(argvi) startSystemServer = true; else if (argvi.startsWith(ABI_LIST_ARG) abiList = argvi.substring(ABI_LIST_ARG.length(); else if (argvi.startsWith(SOCKET_NAME_ARG) socketName = argvi

14、.substring(SOCKET_NAME_ARG.length(); else throw new RuntimeException("Unknown command line argument: " + argvi); . /预加载android依赖的文件 preload(); . if (startSystemServer) /启动系统服务 startSystemServer(abiList, socketName); . catch (MethodAndArgsCaller caller) caller.run(); catch (Throwable ex) Lo

15、g.e(TAG, "Zygote died with exception", ex); closeServerSocket(); throw ex; 看这个类的main方法，最上面根据传入的参数判断是否将startSystemServer这个标记设为true，接着预加载android依赖的文件，最后根据上面设置的标记来判断是否能启动系统服务。接着看ZygoteInit.java中main方法在最后调用startSystemServer方法具体内容 private static boolean startSystemServer(String abiList, String

16、socketName) throws MethodAndArgsCaller, RuntimeException . /* Hardcoded command line to start the system server */ String args = "-setuid=1000", "-setgid=1000", "-setgroups=1001,1002,1003,1004,1005,1006,1007,1008,1009,1010,1018,1021,1032,3001,3002,3003,3006,3007,3009,3010&qu

17、ot;, "-capabilities=" + capabilities + "," + capabilities, "-nice-name=system_server", "-runtime-args", "com.android.server.SystemServer", ; . try parsedArgs = new ZygoteConnection.Arguments(args); ZygoteConnection.applyDebuggerSystemProperty(parsedA

18、rgs); ZygoteConnection.applyInvokeWithSystemProperty(parsedArgs); /Zygote进程开始fork子进程，启动SystemServer /* Request to fork the system server process */ pid = Zygote.forkSystemServer( parsedArgs.uid, parsedArgs.gid, parsedArgs.gids, parsedArgs.debugFlags, null, parsedArgs.permittedCapabilities, parsedArg

19、s.effectiveCapabilities); catch (IllegalArgumentException ex) throw new RuntimeException(ex); . SystemServer.java 代码/frameworks/base/services/java/com/android/server/SystemServer.java /* * The main entry point from zygote. */ public static void main(String args) new SystemServer().run(); private voi

20、d run() . / Start services. try Trace.traceBegin(Trace.TRACE_TAG_SYSTEM_SERVER, "StartServices"); startBootstrapServices(); /启动核心Service startCoreServices(); /启动其他Service startOtherServices(); catch (Throwable ex) Slog.e("System", "*"); Slog.e("System", "

21、* Failure starting system services", ex); throw ex; finally Trace.traceEnd(Trace.TRACE_TAG_SYSTEM_SERVER); / Loop forever. Looper.loop(); throw new RuntimeException("Main thread loop unexpectedly exited"); 启动SystemServer.java的startOtherServices方法/* * Starts a miscellaneous grab bag of

22、 stuff that has yet to be refactored * and organized. */private void startOtherServices() . / We now tell the activity manager it is okay to run third party / code. It will call back into us once it has gotten to the state / where third party code can really run (but before it has actually / started

23、 launching the initial applications), for us to complete our / initialization. mActivityManagerService.systemReady(new Runnable() Override public void run() Slog.i(TAG, "Making services ready"); . .ActivityManagerService.java中的mStackSupervisor.resumeFocusedStackTopActivityLocked() public v

24、oid systemReady(final Runnable goingCallback) . Slog.i(TAG, "System now ready"); EventLog.writeEvent(EventLogTags.BOOT_PROGRESS_AMS_READY, SystemClock.uptimeMillis(); . synchronized (this) / Only start up encryption-aware persistent apps; once user is / unlocked we'll come back around

25、and start unaware apps startPersistentApps(PackageManager.MATCH_DIRECT_BOOT_AWARE); . /调用ActivityStackSupervisor中的resumeFocusedStackTopActivityLocked方法 mStackSupervisor.resumeFocusedStackTopActivityLocked(); mUserController.sendUserSwitchBroadcastsLocked(-1, currentUserId); ActivityStackSupervisor.j

26、ava中的resumeFocusedStackTopActivityLocked方法 boolean resumeFocusedStackTopActivityLocked() return resumeFocusedStackTopActivityLocked(null, null, null); boolean resumeFocusedStackTopActivityLocked( ActivityStack targetStack, ActivityRecord target, ActivityOptions targetOptions) if (targetStack != ull

27、&& isFocusedStack(targetStack) return targetStack.resumeTopActivityUncheckedLocked(target, targetOptions); final ActivityRecord r = mFocusedStack.topRunningActivityLocked(); if (r = null | r.state != RESUMED) /调用ActivityStack中的resumeTopActivityUncheckedLocked来保证栈中的顶层Activity被重新启动 mFocusedSta

28、ck.resumeTopActivityUncheckedLocked(null, null); return false; ActivityStack.java中的resumeTopActivityUncheckedLocked方法 boolean resumeTopActivityUncheckedLocked(ActivityRecord prev, ActivityOptions options) . boolean result = false; try / Protect against recursion. mStackSupervisor.inResumeTopActivity

29、 = true; if (mService.mLockScreenShown = ActivityManagerService.LOCK_SCREEN_LEAVING) mService.mLockScreenShown = ActivityManagerService.LOCK_SCREEN_HIDDEN; mService.updateSleepIfNeededLocked(); result = resumeTopActivityInnerLocked(prev, options); finally mStackSupervisor.inResumeTopActivity = false

30、; return result; private boolean resumeTopActivityInnerLocked(ActivityRecord prev, ActivityOptions options) if (DEBUG_LOCKSCREEN) mService.logLockScreen(""); if (!mService.mBooting && !mService.mBooted) / Not ready yet! return false; . if (next = null) / There are no more activitie

31、s! final String reason = "noMoreActivities" final int returnTaskType = prevTask = null | !prevTask.isOverHomeStack() ? HOME_ACTIVITY_TYPE : prevTask.getTaskToReturnTo(); if (!mFullscreen && adjustFocusToNextFocusableStackLocked(returnTaskType, reason) / Try to move focus to the next visible stack with a running activity if this / stack is not covering the entire screen. return mStackSupervisor.resumeFocusedStackTopActivityLocked( mStackSupervisor.getFocusedStack(), prev, null); / Let's just start up the Launcher.