本文转载自：http://blog.csdn.net/yangwen123/article/details/8177702

Android系统服务线程都驻留在SystemServer进程中，由SystemServer启动，在SystemServer.init2函数中，通过启动一个线程来启动各种系统服务线程。

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1. public static final void init2() {  
2.         Slog.i(TAG, “Entered the Android system server!”);  
3.         Thread thr = new ServerThread();// 创建一个线程  
4.         thr.setName(“android.server.ServerThread”);//设置线程名称  
5.         thr.start();/启动该线程  
6.     }  

android系统服务都是在thr线程的run函数中启动：

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1. public void run() {  
2.     EventLog.writeEvent(EventLogTags.BOOT_PROGRESS_SYSTEM_RUN,SystemClock.uptimeMillis());  
3.   
4.     Looper.prepare();//创建一个消息循环对象  
5.   
6.     android.os.Process.setThreadPriority(android.os.Process.THREAD_PRIORITY_FOREGROUND);  
7.     BinderInternal.disableBackgroundScheduling(true);  
8.     android.os.Process.setCanSelfBackground(false);  
9.     // Critical services…  
10.     try {  
11.         Slog.i(TAG, “Activity Manager”);  
12.         //①启动ActivityManagerService服务线程  
13.         context = ActivityManagerService.main(factoryTest);  
14.         …………………………………………  
15.         //②向ServiceManager注册自己  
16.         ActivityManagerService.setSystemProcess();  
17.         …………………………………………  
18.         Slog.i(TAG, “System Content Providers”);  
19.         //③安装系统Providers  
20.         ActivityManagerService.installSystemProviders();  
21.         …………………………………………  
22.         //④设置ActivityManagerService的成员变量mWindowManager  
23.         ActivityManagerService.self().setWindowManager(wm);  
24.         …………………………………………  
25.         } catch (RuntimeException e) {  
26.                 Slog.e(“System”, “******************************************”);  
27.                 Slog.e(“System”, “************ Failure starting core service”, e);  
28.                  }  
29.         //⑤调用systemReady函数为系统准备各种服务  
30.         ActivityManagerService.self().systemReady(new Runnable() {  
31.             public void run() {  
32.                 Slog.i(TAG, “Making services ready”);  
33.   
34.                 startSystemUi(contextF);  
35.                 try {  
36.                     if (batteryF != null) batteryF.systemReady();  
37.                 } catch (Throwable e) {  
38.                     reportWtf(“making Battery Service ready”, e);  
39.                 }  
40.                 try {  
41.                     if (networkManagementF != null) networkManagementF.systemReady();  
42.                 } catch (Throwable e) {  
43.                     reportWtf(“making Network Managment Service ready”, e);  
44.                 }  
45.                 try {  
46.                     if (networkStatsF != null) networkStatsF.systemReady();  
47.                 } catch (Throwable e) {  
48.                     reportWtf(“making Network Stats Service ready”, e);  
49.                 }  
50.                 try {  
51.                     if (networkPolicyF != null) networkPolicyF.systemReady();  
52.                 } catch (Throwable e) {  
53.                     reportWtf(“making Network Policy Service ready”, e);  
54.                 }  
55.                 try {  
56.                     if (connectivityF != null) connectivityF.systemReady();  
57.                 } catch (Throwable e) {  
58.                     reportWtf(“making Connectivity Service ready”, e);  
59.                 }  
60.                 try {  
61.                     if (dockF != null) dockF.systemReady();  
62.                 } catch (Throwable e) {  
63.                     reportWtf(“making Dock Service ready”, e);  
64.                 }  
65.                 try {  
66.                     if (usbF != null) usbF.systemReady();  
67.                 } catch (Throwable e) {  
68.                     reportWtf(“making USB Service ready”, e);  
69.                 }  
70.                 try {  
71.                     if (uiModeF != null) uiModeF.systemReady();  
72.                 } catch (Throwable e) {  
73.                     reportWtf(“making UI Mode Service ready”, e);  
74.                 }  
75.                 try {  
76.                     if (recognitionF != null) recognitionF.systemReady();  
77.                 } catch (Throwable e) {  
78.                     reportWtf(“making Recognition Service ready”, e);  
79.                 }  
80.                 Watchdog.getInstance().start();  
81.   
82.                 // It is now okay to let the various system services start their  
83.                 // third party code…  
84.   
85.                 try {  
86.                     if (appWidgetF != null) appWidgetF.systemReady(safeMode);  
87.                 } catch (Throwable e) {  
88.                     reportWtf(“making App Widget Service ready”, e);  
89.                 }  
90.                 try {  
91.                     if (wallpaperF != null) wallpaperF.systemReady();  
92.                 } catch (Throwable e) {  
93.                     reportWtf(“making Wallpaper Service ready”, e);  
94.                 }  
95.                 try {  
96.                     if (immF != null) immF.systemReady(statusBarF);  
97.                 } catch (Throwable e) {  
98.                     reportWtf(“making Input Method Service ready”, e);  
99.                 }  
100.                 try {  
101.                     if (locationF != null) locationF.systemReady();  
102.                 } catch (Throwable e) {  
103.                     reportWtf(“making Location Service ready”, e);  
104.                 }  
105.                 try {  
106.                     if (countryDetectorF != null) countryDetectorF.systemReady();  
107.                 } catch (Throwable e) {  
108.                     reportWtf(“making Country Detector Service ready”, e);  
109.                 }  
110.                 try {  
111.                     if (throttleF != null) throttleF.systemReady();  
112.                 } catch (Throwable e) {  
113.                     reportWtf(“making Throttle Service ready”, e);  
114.                 }  
115.                 try {  
116.                     if (networkTimeUpdaterF != null) networkTimeUpdaterF.systemReady();  
117.                 } catch (Throwable e) {  
118.                     reportWtf(“making Network Time Service ready”, e);  
119.                 }  
120.                 try {  
121.                     if (textServiceManagerServiceF != null) textServiceManagerServiceF.systemReady();  
122.                 } catch (Throwable e) {  
123.                     reportWtf(“making Text Services Manager Service ready”, e);  
124.                 }  
125.             }  
126.         });  
127.     Looper.loop();  
128.     Slog.d(TAG, “System ServerThread is exiting!”);  
129. }  

第一：ActivityManagerService.main(factoryTest)

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1. public static final Context main(int factoryTest) {  
2.     //①启动AThread线程来创建ActivityManagerService实例  
3.     AThread thr = new AThread();  
4.     thr.start();  
5.   
6.     synchronized (thr) {  
7.         while (thr.mService == null) {  
8.             try {  
9.                 thr.wait();  
10.             } catch (InterruptedException e) {  
11.             }  
12.         }  
13.     }  
14.     //将创建的ActivityManagerService实例保存到ActivityManagerService的静态变量mSelf  
15.     ActivityManagerService m = thr.mService;  
16.     mSelf = m;  
17.     //②创建ActivityThread实例并保存到ActivityManagerService的静态变量mSystemThread  
18.     ActivityThread at = ActivityThread.systemMain();  
19.     mSystemThread = at;  
20.     Context context = at.getSystemContext();  
21.     context.setTheme(android.R.style.Theme_Holo);  
22.     m.mContext = context;  
23.     m.mFactoryTest = factoryTest;  
24.     //③创建一个ActivityStack实例，并保存到ActivityManagerService的成员变量mMainStack中  
25.     m.mMainStack = new ActivityStack(m, context, true);  
26.     //④向ServiceManager注册BatteryStatsService服务  
27.     m.mBatteryStatsService.publish(context);  
28.     //⑤向ServiceManager注册UsageStatsService服务  
29.     m.mUsageStatsService.publish(context);  
30.       
31.     synchronized (thr) {  
32.         //取消AThread线程等待，进入消息循环状态  
33.         thr.mReady = true;  
34.         thr.notifyAll();  
35.     }  
36.     //⑥调用startRunning函数  
37.     m.startRunning(null, null, null, null);  
38.       
39.     return context;  
40. }  

①启动AThread线程

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1. static class AThread extends Thread {  
2.     ActivityManagerService mService;  
3.     boolean mReady = false;  
4.   
5.     public AThread() {  
6.         super(“ActivityManager”);  
7.     }  
8.   
9.     public void run() {  
10.         //创建消息循环对象  
11.         Looper.prepare();  
12.         android.os.Process.setThreadPriority(android.os.Process.THREAD_PRIORITY_FOREGROUND);  
13.         android.os.Process.setCanSelfBackground(false);  
14.         ActivityManagerService m = new ActivityManagerService();  
15.         synchronized (this) {  
16.             //创建ActivityManagerService实例  
17.             mService = m;  
18.             notifyAll();  
19.         }  
20.         //mReady = false，所以该线程处于等待  
21.         synchronized (this) {  
22.             while (!mReady) {  
23.                 try {  
24.                     wait();  
25.                 } catch (InterruptedException e) {  
26.                 }  
27.             }  
28.         }  
29.         // For debug builds, log event loop stalls to dropbox for analysis.  
30.         if (StrictMode.conditionallyEnableDebugLogging()) {  
31.             Slog.i(TAG, “Enabled StrictMode logging for AThread’s Looper”);  
32.         }  
33.         //开启该线程的消息循环  
34.         Looper.loop();  
35.     }  
36. }  

②创建ActivityThread实例

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1. public static final ActivityThread systemMain() {  
2.     HardwareRenderer.disable(true);  
3.     ActivityThread thread = new ActivityThread();  
4.     thread.attach(true);  
5.     return thread;  
6. }  

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1. private void attach(boolean system) {  
2.     //本地线程存储  
3.     sThreadLocal.set(this);  
4.     mSystemThread = system;//mSystemThread=true  
5.     if (!system) {  
6.         ViewRootImpl.addFirstDrawHandler(new Runnable() {  
7.             public void run() {  
8.                 ensureJitEnabled();  
9.             }  
10.         });  
11.         android.ddm.DdmHandleAppName.setAppName(“<pre-initialized>”);  
12.         RuntimeInit.setApplicationObject(mAppThread.asBinder());  
13.         IActivityManager mgr = ActivityManagerNative.getDefault();  
14.         try {  
15.             mgr.attachApplication(mAppThread);  
16.         } catch (RemoteException ex) {  
17.             // Ignore  
18.         }  
19.     } else {  
20.         // Don’t set application object here — if the system crashes,  
21.         // we can’t display an alert, we just want to die die die.  
22.         android.ddm.DdmHandleAppName.setAppName(“system_process”);  
23.         try {  
24.             mInstrumentation = new Instrumentation();  
25.             ContextImpl context = new ContextImpl();  
26.             context.init(getSystemContext().mPackageInfo, null, this);  
27.             //创建Application实例，并保存在成员变量mAllApplications中  
28.             Application app = Instrumentation.newApplication(Application.class, context);  
29.             mAllApplications.add(app);  
30.             mInitialApplication = app;  
31.             //调用应用程序的onCreate函数  
32.             app.onCreate();  
33.         } catch (Exception e) {  
34.             throw new RuntimeException(  
35.                     “Unable to instantiate Application():” + e.toString(), e);  
36.         }  
37.     }  
38.       
39.     ViewRootImpl.addConfigCallback(new ComponentCallbacks2() {  
40.         public void onConfigurationChanged(Configuration newConfig) {  
41.             synchronized (mPackages) {  
42.                 // We need to apply this change to the resources  
43.                 // immediately, because upon returning the view  
44.                 // hierarchy will be informed about it.  
45.                 if (applyConfigurationToResourcesLocked(newConfig, null)) {  
46.                     // This actually changed the resources!  Tell  
47.                     // everyone about it.  
48.                     if (mPendingConfiguration == null ||  
49.                             mPendingConfiguration.isOtherSeqNewer(newConfig)) {  
50.                         mPendingConfiguration = newConfig;  
51.                           
52.                         queueOrSendMessage(H.CONFIGURATION_CHANGED, newConfig);  
53.                     }  
54.                 }  
55.             }  
56.         }  
57.         public void onLowMemory() {  
58.         }  
59.         public void onTrimMemory(int level) {  
60.         }  
61.     });  
62. }  

③创建一个ActivityStack实例

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1. ActivityStack(ActivityManagerService service, Context context, boolean mainStack) {  
2.     mService = service;  
3.     mContext = context;  
4.     mMainStack = mainStack;  
5.     PowerManager pm =(PowerManager)context.getSystemService(Context.POWER_SERVICE);  
6.     mGoingToSleep = pm.newWakeLock(PowerManager.PARTIAL_WAKE_LOCK, “ActivityManager-Sleep”);  
7.     mLaunchingActivity = pm.newWakeLock(PowerManager.PARTIAL_WAKE_LOCK, “ActivityManager-Launch”);  
8.     mLaunchingActivity.setReferenceCounted(false);  
9. }  

④注册BatteryStatsService服务

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1. public void publish(Context context) {  
2.     mContext = context;  
3.     ServiceManager.addService(“batteryinfo”, asBinder());  
4.     mStats.setNumSpeedSteps(new PowerProfile(mContext).getNumSpeedSteps());  
5.     mStats.setRadioScanningTimeout(mContext.getResources().getInteger(  
6.             com.android.internal.R.integer.config_radioScanningTimeout)* 1000L);  
7. }  

⑤注册UsageStatsService服务

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1. public void publish(Context context) {  
2.         mContext = context;  
3.         ServiceManager.addService(SERVICE_NAME, asBinder());  
4. }  

⑥调用startRunning函数startRunning(null, null, null, null)

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1. public final void startRunning(String pkg, String cls, String action,String data) {  
2.     synchronized(this) {  
3.         //mStartRunning = false  
4.         if (mStartRunning) {  
5.             return;  
6.         }  
7.         mStartRunning = true;  
8.         //mTopComponent=null  
9.         mTopComponent = pkg != null && cls != null? new ComponentName(pkg, cls) : null;  
10.         //mTopAction=Intent.ACTION_MAIN  
11.         mTopAction = action != null ? action : Intent.ACTION_MAIN;  
12.         //mTopData=null  
13.         mTopData = data;  
14.         if (!mSystemReady) {  
15.             return;  
16.         }  
17.     }  
18.     systemReady(null);  
19. }  

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1. public void systemReady(final Runnable goingCallback) {  
2.     //goingCallback = null  
3.     synchronized(this) {  
4.         //mSystemReady = false  
5.         if (mSystemReady) {  
6.             if (goingCallback != null) goingCallback.run();  
7.             return;  
8.         }  
9.           
10.         // mDidUpdate = false  
11.         if (!mDidUpdate) {  
12.             if (mWaitingUpdate) {  
13.                 return;  
14.             }  
15.             Intent intent = new Intent(Intent.ACTION_PRE_BOOT_COMPLETED);  
16.             List<ResolveInfo> ris = null;  
17.             try {  
18.                 ris = AppGlobals.getPackageManager().queryIntentReceivers(intent, null, 0);  
19.             } catch (RemoteException e) {  
20.             }  
21.             if (ris != null) {  
22.                 for (int i=ris.size()-1; i>=0; i–) {  
23.                     if ((ris.get(i).activityInfo.applicationInfo.flags&ApplicationInfo.FLAG_SYSTEM) == 0) {  
24.                         ris.remove(i);  
25.                     }  
26.                 }  
27.                 intent.addFlags(Intent.FLAG_RECEIVER_BOOT_UPGRADE);  
28.                   
29.                 ArrayList<ComponentName> lastDoneReceivers = readLastDonePreBootReceivers();  
30.                   
31.                 final ArrayList<ComponentName> doneReceivers = new ArrayList<ComponentName>();  
32.                 for (int i=0; i<ris.size(); i++) {  
33.                     ActivityInfo ai = ris.get(i).activityInfo;  
34.                     ComponentName comp = new ComponentName(ai.packageName, ai.name);  
35.                     if (lastDoneReceivers.contains(comp)) {  
36.                         ris.remove(i);  
37.                         i–;  
38.                     }  
39.                 }  
40.   
41.                 for (int i=0; i<ris.size(); i++) {  
42.                     ActivityInfo ai = ris.get(i).activityInfo;  
43.                     ComponentName comp = new ComponentName(ai.packageName, ai.name);  
44.                     doneReceivers.add(comp);  
45.                     intent.setComponent(comp);  
46.                     IIntentReceiver finisher = null;  
47.                     if (i == ris.size()-1) {  
48.                         finisher = new IIntentReceiver.Stub() {  
49.                             public void performReceive(Intent intent, int resultCode,  
50.                                     String data, Bundle extras, boolean ordered,  
51.                                     boolean sticky) {  
52.                                 // The raw IIntentReceiver interface is called  
53.                                 // with the AM lock held, so redispatch to  
54.                                 // execute our code without the lock.  
55.                                 mHandler.post(new Runnable() {  
56.                                     public void run() {  
57.                                         synchronized (ActivityManagerService.this) {  
58.                                             mDidUpdate = true;  
59.                                         }  
60.                                         writeLastDonePreBootReceivers(doneReceivers);  
61.                                         showBootMessage(mContext.getText(  
62.                                                 R.string.android_upgrading_complete),false);  
63.                                         systemReady(goingCallback);  
64.                                     }  
65.                                 });  
66.                             }  
67.                         };  
68.                     }  
69.                     Slog.i(TAG, “Sending system update to: ” + intent.getComponent());  
70.                     broadcastIntentLocked(null, null, intent, null, finisher,  
71.                             0, null, null, null, true, false, MY_PID, Process.SYSTEM_UID);  
72.                     if (finisher != null) {  
73.                         mWaitingUpdate = true;  
74.                     }  
75.                 }  
76.             }  
77.             if (mWaitingUpdate) {  
78.                 return;  
79.             }  
80.             mDidUpdate = true;  
81.         }  
82.           
83.         mSystemReady = true;  
84.         if (!mStartRunning) {  
85.             return;  
86.         }  
87.     }  
88.   
89.     ArrayList<ProcessRecord> procsToKill = null;  
90.     synchronized(mPidsSelfLocked) {  
91.         for (int i=mPidsSelfLocked.size()-1; i>=0; i–) {  
92.             ProcessRecord proc = mPidsSelfLocked.valueAt(i);  
93.             if (!isAllowedWhileBooting(proc.info)){  
94.                 if (procsToKill == null) {  
95.                     procsToKill = new ArrayList<ProcessRecord>();  
96.                 }  
97.                 procsToKill.add(proc);  
98.             }  
99.         }  
100.     }  
101.       
102.     synchronized(this) {  
103.         if (procsToKill != null) {  
104.             for (int i=procsToKill.size()-1; i>=0; i–) {  
105.                 ProcessRecord proc = procsToKill.get(i);  
106.                 Slog.i(TAG, “Removing system update proc: ” + proc);  
107.                 removeProcessLocked(proc, true, false, “system update done”);  
108.             }  
109.         }  
110.           
111.         // Now that we have cleaned up any update processes, we  
112.         // are ready to start launching real processes and know that  
113.         // we won’t trample on them any more.  
114.         mProcessesReady = true;  
115.     }  
116.       
117.     Slog.i(TAG, “System now ready”);  
118.     EventLog.writeEvent(EventLogTags.BOOT_PROGRESS_AMS_READY,SystemClock.uptimeMillis());  
119.   
120.     synchronized(this) {  
121.         // Make sure we have no pre-ready processes sitting around.  
122.           
123.         if (mFactoryTest == SystemServer.FACTORY_TEST_LOW_LEVEL) {  
124.             ResolveInfo ri = mContext.getPackageManager().resolveActivity(new Intent(Intent.ACTION_FACTORY_TEST),STOCK_PM_FLAGS);  
125.             CharSequence errorMsg = null;  
126.             if (ri != null) {  
127.                 ActivityInfo ai = ri.activityInfo;  
128.                 ApplicationInfo app = ai.applicationInfo;  
129.                 if ((app.flags&ApplicationInfo.FLAG_SYSTEM) != 0) {  
130.                     mTopAction = Intent.ACTION_FACTORY_TEST;  
131.                     mTopData = null;  
132.                     mTopComponent = new ComponentName(app.packageName,  
133.                             ai.name);  
134.                 } else {  
135.                     errorMsg = mContext.getResources().getText(com.android.internal.R.string.factorytest_not_system);  
136.                 }  
137.             } else {  
138.                 errorMsg = mContext.getResources().getText(com.android.internal.R.string.factorytest_no_action);  
139.             }  
140.             if (errorMsg != null) {  
141.                 mTopAction = null;  
142.                 mTopData = null;  
143.                 mTopComponent = null;  
144.                 Message msg = Message.obtain();  
145.                 msg.what = SHOW_FACTORY_ERROR_MSG;  
146.                 msg.getData().putCharSequence(“msg”, errorMsg);  
147.                 mHandler.sendMessage(msg);  
148.             }  
149.         }  
150.     }  
151.   
152.     retrieveSettings();  
153.   
154.     if (goingCallback != null) goingCallback.run();  
155.       
156.     synchronized (this) {  
157.         if (mFactoryTest != SystemServer.FACTORY_TEST_LOW_LEVEL) {  
158.             try {  
159.                 List apps = AppGlobals.getPackageManager().getPersistentApplications(STOCK_PM_FLAGS);  
160.                 if (apps != null) {  
161.                     int N = apps.size();  
162.                     int i;  
163.                     for (i=0; i<N; i++) {  
164.                         ApplicationInfo info= (ApplicationInfo)apps.get(i);  
165.                         if (info != null &&!info.packageName.equals(“android”)) {  
166.                             addAppLocked(info);  
167.                         }  
168.                     }  
169.                 }  
170.             } catch (RemoteException ex) {  
171.                 // pm is in same process, this will never happen.  
172.             }  
173.         }  
174.   
175.         // Start up initial activity.  
176.         mBooting = true;  
177.           
178.         try {  
179.             if (AppGlobals.getPackageManager().hasSystemUidErrors()) {  
180.                 Message msg = Message.obtain();  
181.                 msg.what = SHOW_UID_ERROR_MSG;  
182.                 mHandler.sendMessage(msg);  
183.             }  
184.         } catch (RemoteException e) {  
185.         }  
186.   
187.         mMainStack.resumeTopActivityLocked(null);  
188.     }  
189. }  

第二：ActivityManagerService.setSystemProcess()

[java] 
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1. public static void setSystemProcess() {  
2.     try {  
3.         ActivityManagerService m = mSelf;  
4.           
5.         ServiceManager.addService(“activity”, m);  
6.         ServiceManager.addService(“meminfo”, new MemBinder(m));  
7.         ServiceManager.addService(“gfxinfo”, new GraphicsBinder(m));  
8.         if (MONITOR_CPU_USAGE) {  
9.             ServiceManager.addService(“cpuinfo”, new CpuBinder(m));  
10.         }  
11.         ServiceManager.addService(“permission”, new PermissionController(m));  
12.         //把应用程序框架层下面的android包加载进来  
13.         ApplicationInfo info =mSelf.mContext.getPackageManager().getApplicationInfo(“android”, STOCK_PM_FLAGS);  
14.         mSystemThread.installSystemApplicationInfo(info);  
15.      
16.         synchronized (mSelf) {  
17.             ProcessRecord app = mSelf.newProcessRecordLocked(  
18.                     mSystemThread.getApplicationThread(), info,info.processName);  
19.             app.persistent = true;  
20.             app.pid = MY_PID;  
21.             app.maxAdj = ProcessList.SYSTEM_ADJ;  
22.             mSelf.mProcessNames.put(app.processName, app.info.uid, app);  
23.             synchronized (mSelf.mPidsSelfLocked) {  
24.                 mSelf.mPidsSelfLocked.put(app.pid, app);  
25.             }  
26.             mSelf.updateLruProcessLocked(app, true, true);  
27.         }  
28.     } catch (PackageManager.NameNotFoundException e) {  
29.         throw new RuntimeException(  
30.                 “Unable to find android system package”, e);  
31.     }  
32. }  

第三：ActivityManagerService.installSystemProviders()

[java] 
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1. public static final void installSystemProviders() {  
2.         List<ProviderInfo> providers;  
3.         synchronized (mSelf) {  
4.             ProcessRecord app = mSelf.mProcessNames.get(“system”, Process.SYSTEM_UID);  
5.             providers = mSelf.generateApplicationProvidersLocked(app);  
6.             if (providers != null) {  
7.                 for (int i=providers.size()-1; i>=0; i–) {  
8.                     ProviderInfo pi = (ProviderInfo)providers.get(i);  
9.                     if ((pi.applicationInfo.flags&ApplicationInfo.FLAG_SYSTEM) == 0) {  
10.                         Slog.w(TAG, “Not installing system proc provider ” + pi.name  
11.                                 + “: not system .apk”);  
12.                         providers.remove(i);  
13.                     }  
14.                 }  
15.             }  
16.         }  
17.         if (providers != null) {  
18.             mSystemThread.installSystemProviders(providers);  
19.         }  
20.   
21.         mSelf.mCoreSettingsObserver = new CoreSettingsObserver(mSelf);  
22.   
23.         mSelf.mUsageStatsService.monitorPackages();  
24.     }  

第三：ActivityManagerService.systemReady()