system_server进程创建流程_systemserver创建过程

system_server 进程是 Zygote 进程 fork 出的第一个进程，它负责管理和启动整个 Framework 层，下面附上android系统启动流程图：

记得上一篇Zygote进程创建里面提到过，forckSystemServer创建system_server进程。

/frameworks/base/core/java/com/android/internal/os/ZygoteInit.java 中代码如下:

下面是forkSystemServer 里面的代码: 

 Zygote.forkSystemServer 返回的是一个int型的pid,如果pid不等于0,代表的是在父进程中执行，即

Zygote进程，如果pid等于0，代表在子进程中执行。

 最终执行handleSystemServerProcess,是在system_server进程中执行。

接下来看handleSystemServerProcess方法

 /**
499       * Finish remaining work for the newly forked system server process.
500       */
501      private static Runnable handleSystemServerProcess(ZygoteArguments parsedArgs) {
502          // set umask to 0077 so new files and directories will default to owner-only permissions.
503          Os.umask(S_IRWXG | S_IRWXO);
504  
505          if (parsedArgs.mNiceName != null) {
506              Process.setArgV0(parsedArgs.mNiceName);
507          }
508  
509          final String systemServerClasspath = Os.getenv("SYSTEMSERVERCLASSPATH");
510          if (systemServerClasspath != null) {
511              performSystemServerDexOpt(systemServerClasspath);
512              // Capturing profiles is only supported for debug or eng builds since selinux normally
513              // prevents it.
514              if (shouldProfileSystemServer() && (Build.IS_USERDEBUG || Build.IS_ENG)) {
515                  try {
516                      Log.d(TAG, "Preparing system server profile");
517                      prepareSystemServerProfile(systemServerClasspath);
518                  } catch (Exception e) {
519                      Log.wtf(TAG, "Failed to set up system server profile", e);
520                  }
521              }
522          }
523  
524          if (parsedArgs.mInvokeWith != null) {
525              String[] args = parsedArgs.mRemainingArgs;
526              // If we have a non-null system server class path, we'll have to duplicate the
527              // existing arguments and append the classpath to it. ART will handle the classpath
528              // correctly when we exec a new process.
529              if (systemServerClasspath != null) {
530                  String[] amendedArgs = new String[args.length + 2];
531                  amendedArgs[0] = "-cp";
532                  amendedArgs[1] = systemServerClasspath;
533                  System.arraycopy(args, 0, amendedArgs, 2, args.length);
534                  args = amendedArgs;
535              }
536  
537              WrapperInit.execApplication(parsedArgs.mInvokeWith,
538                      parsedArgs.mNiceName, parsedArgs.mTargetSdkVersion,
539                      VMRuntime.getCurrentInstructionSet(), null, args);
540  
541              throw new IllegalStateException("Unexpected return from WrapperInit.execApplication");
542          } else {
543              ClassLoader cl = null;
544              if (systemServerClasspath != null) {
545                  cl = createPathClassLoader(systemServerClasspath, parsedArgs.mTargetSdkVersion);
546  
547                  Thread.currentThread().setContextClassLoader(cl);
548              }
549  
550              /*
551               * Pass the remaining arguments to SystemServer.
552               */
553              return ZygoteInit.zygoteInit(parsedArgs.mTargetSdkVersion,
554                      parsedArgs.mDisabledCompatChanges,
555                      parsedArgs.mRemainingArgs, cl);
556          }
557  
558          /* should never reach here */
559      }

 最终执行到ZygoteInit.zygoteInit方法，点进去看一下

     /**
978       * The main function called when started through the zygote process. This could be unified with
979       * main(), if the native code in nativeFinishInit() were rationalized with Zygote startup.<p>
980       *
981       * Current recognized args:
982       * <ul>
983       * <li> <code> [--] &lt;start class name&gt;  &lt;args&gt;
984       * </ul>
985       *
986       * @param targetSdkVersion target SDK version
987       * @param disabledCompatChanges set of disabled compat changes for the process (all others
988       *                              are enabled)
989       * @param argv             arg strings
990       */
991      public static final Runnable zygoteInit(int targetSdkVersion, long[] disabledCompatChanges,
992              String[] argv, ClassLoader classLoader) {
993          if (RuntimeInit.DEBUG) {
994              Slog.d(RuntimeInit.TAG, "RuntimeInit: Starting application from zygote");
995          }
996  
997          Trace.traceBegin(Trace.TRACE_TAG_ACTIVITY_MANAGER, "ZygoteInit");
998          RuntimeInit.redirectLogStreams();
999  
1000          RuntimeInit.commonInit();
1001          ZygoteInit.nativeZygoteInit();
1002          return RuntimeInit.applicationInit(targetSdkVersion, disabledCompatChanges, argv,
1003                  classLoader);
1004      }

再看看RuntimeInit.applicationInit方法

 protected static Runnable applicationInit(int targetSdkVersion, long[] disabledCompatChanges,
405              String[] argv, ClassLoader classLoader) {
406          // If the application calls System.exit(), terminate the process
407          // immediately without running any shutdown hooks.  It is not possible to
408          // shutdown an Android application gracefully.  Among other things, the
409          // Android runtime shutdown hooks close the Binder driver, which can cause
410          // leftover running threads to crash before the process actually exits.
411          nativeSetExitWithoutCleanup(true);
412  
413          VMRuntime.getRuntime().setTargetSdkVersion(targetSdkVersion);
414          VMRuntime.getRuntime().setDisabledCompatChanges(disabledCompatChanges);
415  
416          final Arguments args = new Arguments(argv);
417  
418          // The end of of the RuntimeInit event (see #zygoteInit).
419          Trace.traceEnd(Trace.TRACE_TAG_ACTIVITY_MANAGER);
420  
421          // Remaining arguments are passed to the start class's static main
422          return findStaticMain(args.startClass, args.startArgs, classLoader);
423      }

 最终执行的是findStaticMain方法

 /**
337       * Invokes a static "main(argv[]) method on class "className".
338       * Converts various failing exceptions into RuntimeExceptions, with
339       * the assumption that they will then cause the VM instance to exit.
340       *
341       * @param className Fully-qualified class name
342       * @param argv Argument vector for main()
343       * @param classLoader the classLoader to load {@className} with
344       */
345      protected static Runnable findStaticMain(String className, String[] argv,
346              ClassLoader classLoader) {
347          Class<?> cl;
348  
349          try {
350              cl = Class.forName(className, true, classLoader);
351          } catch (ClassNotFoundException ex) {
352              throw new RuntimeException(
353                      "Missing class when invoking static main " + className,
354                      ex);
355          }
356  
357          Method m;
358          try {
359              m = cl.getMethod("main", new Class[] { String[].class });
360          } catch (NoSuchMethodException ex) {
361              throw new RuntimeException(
362                      "Missing static main on " + className, ex);
363          } catch (SecurityException ex) {
364              throw new RuntimeException(
365                      "Problem getting static main on " + className, ex);
366          }
367  
368          int modifiers = m.getModifiers();
369          if (! (Modifier.isStatic(modifiers) && Modifier.isPublic(modifiers))) {
370              throw new RuntimeException(
371                      "Main method is not public and static on " + className);
372          }
373  
374          /*
375           * This throw gets caught in ZygoteInit.main(), which responds
376           * by invoking the exception's run() method. This arrangement
377           * clears up all the stack frames that were required in setting
378           * up the process.
379           */
380          return new MethodAndArgsCaller(m, argv);
381      }

 再看看 MethodAndArgsCaller

  /**
575       * Helper class which holds a method and arguments and can call them. This is used as part of
576       * a trampoline to get rid of the initial process setup stack frames.
577       */
578      static class MethodAndArgsCaller implements Runnable {
579          /** method to call */
580          private final Method mMethod;
581  
582          /** argument array */
583          private final String[] mArgs;
584  
585          public MethodAndArgsCaller(Method method, String[] args) {
586              mMethod = method;
587              mArgs = args;
588          }
589  
590          public void run() {
591              try {
592                  mMethod.invoke(null, new Object[] { mArgs });
593              } catch (IllegalAccessException ex) {
594                  throw new RuntimeException(ex);
595              } catch (InvocationTargetException ex) {
596                  Throwable cause = ex.getCause();
597                  if (cause instanceof RuntimeException) {
598                      throw (RuntimeException) cause;
599                  } else if (cause instanceof Error) {
600                      throw (Error) cause;
601                  }
602                  throw new RuntimeException(ex);
603              }
604          }
605      }
606  }

这样一看就知道通过反射来调用方法的

最后回过头来看下顶部的代码图片

返回的Runnable对象，执行run, 执行system_server main 方法,然后return了。

接下来我们看SystemServer main 方法

/**
411       * The main entry point from zygote.
412       */
413      public static void main(String[] args) {
414          new SystemServer().run();
415      }

run代码中大致分为11个步骤：

1.设定时间

//
450              // Default the timezone property to GMT if not set.
451              //
452              String timezoneProperty = SystemProperties.get("persist.sys.timezone");
453              if (timezoneProperty == null || timezoneProperty.isEmpty()) {
454                  Slog.w(TAG, "Timezone not set; setting to GMT.");
455                  SystemProperties.set("persist.sys.timezone", "GMT");
456              }
457  

2.设定语言

// If the system has "persist.sys.language" and friends set, replace them with
459              // "persist.sys.locale". Note that the default locale at this point is calculated
460              // using the "-Duser.locale" command line flag. That flag is usually populated by
461              // AndroidRuntime using the same set of system properties, but only the system_server
462              // and system apps are allowed to set them.
463              //
464              // NOTE: Most changes made here will need an equivalent change to
465              // core/jni/AndroidRuntime.cpp
466              if (!SystemProperties.get("persist.sys.language").isEmpty()) {
467                  final String languageTag = Locale.getDefault().toLanguageTag();
468  
469                  SystemProperties.set("persist.sys.locale", languageTag);
470                  SystemProperties.set("persist.sys.language", "");
471                  SystemProperties.set("persist.sys.country", "");
472                  SystemProperties.set("persist.sys.localevar", "");
473              }
474  

3.虚拟机库文件路径

  // In case the runtime switched since last boot (such as when
498              // the old runtime was removed in an OTA), set the system
499              // property so that it is in sync. We can't do this in
500              // libnativehelper's JniInvocation::Init code where we already
501              // had to fallback to a different runtime because it is
502              // running as root and we need to be the system user to set
503              // the property. http://b/11463182
504              SystemProperties.set("persist.sys.dalvik.vm.lib.2", VMRuntime.getRuntime().vmLibrary());

4.清除内存使用上限

 // Mmmmmm... more memory!
507              VMRuntime.getRuntime().clearGrowthLimit();

5.设定指纹使用

             // Some devices rely on runtime fingerprint generation, so make sure
510              // we've defined it before booting further.
511              Build.ensureFingerprintProperty();

6.设定环境变量访问用户条件

             // Within the system server, it is an error to access Environment paths without
514              // explicitly specifying a user.
515              Environment.setUserRequired(true);

7.设定binder服务永远运行在前台

             // Ensure binder calls into the system always run at foreground priority.
525              BinderInternal.disableBackgroundScheduling(true);

8.设定线程池最大线程数

 
527              // Increase the number of binder threads in system_server
528              BinderInternal.setMaxThreads(sMaxBinderThreads);

9.启动各种服务

 // Start services.
594          try {
595              t.traceBegin("StartServices");
596              startBootstrapServices(t);
597              startCoreServices(t);
598              startOtherServices(t);
599          } catch (Throwable ex) {
600              Slog.e("System", "******************************************");
601              Slog.e("System", "************ Failure starting system services", ex);
602              throw ex;
603          } finally {
604              t.traceEnd(); // StartServices
605          }
606  
607          StrictMode.initVmDefaults(null);
608  
609          if (!mRuntimeRestart && !isFirstBootOrUpgrade()) {
610              final long uptimeMillis = SystemClock.elapsedRealtime();
611              FrameworkStatsLog.write(FrameworkStatsLog.BOOT_TIME_EVENT_ELAPSED_TIME_REPORTED,
612                      FrameworkStatsLog.BOOT_TIME_EVENT_ELAPSED_TIME__EVENT__SYSTEM_SERVER_READY,
613                      uptimeMillis);
614              final long maxUptimeMillis = 60 * 1000;
615              if (uptimeMillis > maxUptimeMillis) {
616                  Slog.wtf(SYSTEM_SERVER_TIMING_TAG,
617                          "SystemServer init took too long. uptimeMillis=" + uptimeMillis);
618              }
619          }
620  
621          // Diagnostic to ensure that the system is in a base healthy state. Done here as a common
622          // non-zygote process.
623          if (!VMRuntime.hasBootImageSpaces()) {
624              Slog.wtf(TAG, "Runtime is not running with a boot image!");
625          }
626  

10.服务开启循环

  // Loop forever.
628          Looper.loop();

启动系统上下文

   // Initialize the system context.
556              createSystemContext();

 private void createSystemContext() {
696          ActivityThread activityThread = ActivityThread.systemMain();
697          mSystemContext = activityThread.getSystemContext();
698          mSystemContext.setTheme(DEFAULT_SYSTEM_THEME);
699  
700          final Context systemUiContext = activityThread.getSystemUiContext();
701          systemUiContext.setTheme(DEFAULT_SYSTEM_THEME);
702      }

创建SystemServiceManager

 
561              // Create the system service manager.
562              mSystemServiceManager = new SystemServiceManager(mSystemContext);
563              mSystemServiceManager.setStartInfo(mRuntimeRestart,
564                      mRuntimeStartElapsedTime, mRuntimeStartUptime);
565              LocalServices.addService(SystemServiceManager.class, mSystemServiceManager);
566              // Prepare the thread pool for init tasks that can be parallelized
567              SystemServerInitThreadPool.start();