ActivityManagerService（簡稱AMS）是Android系統(tǒng)的核心服務(wù)之一。它的主要作用是管理系統(tǒng)中所有應(yīng)用進程以及應(yīng)用進程中的四大組件。
AMS的啟動過程
接上篇SystemServer run( )方法，AMS的啟動過程主要包含在如下兩個方法中：
private void run() {
...
startBootstrapServices();//創(chuàng)建并啟動AMS服務(wù)，同時執(zhí)行AMS啟動后的一些初始化工作
startOtherServices();// 進入下個階段的一些準備工作
...
}
接下來按這兩個方法來分析
一、startBootstrapServices( )
1.1 創(chuàng)建并啟動AMS服務(wù)
private void startBootstrapServices() {
...
//啟動AMS服務(wù)
mActivityManagerService = mSystemServiceManager.startService(
ActivityManagerService.Lifecycle.class).getService();
//設(shè)置AMS的系統(tǒng)服務(wù)管理器
mActivityManagerService.setSystemServiceManager(mSystemServiceManager);
//設(shè)置AMS的APP安裝器
mActivityManagerService.setInstaller(installer);
//初始化AMS相關(guān)的PMS
mActivityManagerService.initPowerManagement();
...
//想ServiceManager注冊一系列服務(wù),并創(chuàng)建system_server對應(yīng)的ProcessRecord并初始化
mActivityManagerService.setSystemProcess();
}
我們知道SystemServiceManager.startService是通過反射創(chuàng)建服務(wù)對象，并啟動。但是這里傳進去的是AMS的Lifecycle。Lifecycle是AMS中的一個靜態(tài)內(nèi)部類，它繼承SystemService，由它來代理處理AMS的的創(chuàng)建與啟動。
public static final class Lifecycle extends SystemService {
private final ActivityManagerService mService;
public Lifecycle(Context context) {
super(context);
mService = new ActivityManagerService(context);
}
@Override
public void onStart() {
mService.start();
}
public ActivityManagerService getService() {
return mService;
}
}
這樣SystemServiceManager間接通過調(diào)用Lifecycle創(chuàng)建并啟動了AMS服務(wù)。AMS是運行在system_server進程中的Framework服務(wù)，經(jīng)過SystemServiceManager創(chuàng)建的服務(wù)會統(tǒng)一保存在隊列管理。
1.2、AMS初始化工作
1.2.1 ActivityManagerService的構(gòu)造方法：
public ActivityManagerService(Context systemContext) {
mContext = systemContext;
mFactoryTest = FactoryTest.getMode();//默認為FACTORY_TEST_OFF
mSystemThread = ActivityThread.currentActivityThread();
//創(chuàng)建名為"ActivityManager"的前臺線程，并獲取mHandler
mHandlerThread = new ServiceThread(TAG, android.os.Process.THREAD_PRIORITY_FOREGROUND, false);
mHandlerThread.start();
mHandler = new MainHandler(mHandlerThread.getLooper());
//通過UiThread類，創(chuàng)建名為"android.ui"的線程
mUiHandler = new UiHandler();
//前臺廣播接收器，在運行超過10s將放棄執(zhí)行
mFgBroadcastQueue = new BroadcastQueue(this, mHandler,
"foreground", BROADCAST_FG_TIMEOUT, false);
//后臺廣播接收器，在運行超過60s將放棄執(zhí)行
mBgBroadcastQueue = new BroadcastQueue(this, mHandler,
"background", BROADCAST_BG_TIMEOUT, true);
mBroadcastQueues[0] = mFgBroadcastQueue;
mBroadcastQueues[1] = mBgBroadcastQueue;
//創(chuàng)建ActiveServices，其中非低內(nèi)存手機mMaxStartingBackground為8
mServices = new ActiveServices(this);
mProviderMap = new ProviderMap(this);
//創(chuàng)建目錄/data/system
File dataDir = Environment.getDataDirectory();
File systemDir = new File(dataDir, "system");
systemDir.mkdirs();
//創(chuàng)建服務(wù)BatteryStatsService
mBatteryStatsService = new BatteryStatsService(systemDir, mHandler);
mBatteryStatsService.getActiveStatistics().readLocked();
...
//創(chuàng)建進程統(tǒng)計服務(wù)，信息保存在目錄/data/system/procstats，
mProcessStats = new ProcessStatsService(this, new File(systemDir, "procstats"));
mAppOpsService = new AppOpsService(new File(systemDir, "appops.xml"), mHandler);
mGrantFile = new AtomicFile(new File(systemDir, "urigrants.xml"));
// User 0是第一個，也是唯一的一個開機過程中運行的用戶
mStartedUsers.put(UserHandle.USER_OWNER, new UserState(UserHandle.OWNER, true));
mUserLru.add(UserHandle.USER_OWNER);
updateStartedUserArrayLocked();
...
//CPU使用情況的追蹤器執(zhí)行初始化
mProcessCpuTracker.init();
...
mRecentTasks = new RecentTasks(this);
// 創(chuàng)建ActivityStackSupervisor對象
mStackSupervisor = new ActivityStackSupervisor(this, mRecentTasks);
mTaskPersister = new TaskPersister(systemDir, mStackSupervisor, mRecentTasks);
//創(chuàng)建名為"CpuTracker"的線程
mProcessCpuThread = new Thread("CpuTracker") {
public void run() {
while (true) {
try {
try {
synchronized(this) {
final long now = SystemClock.uptimeMillis();
long nextCpuDelay = (mLastCpuTime.get()+MONITOR_CPU_MAX_TIME)-now;
long nextWriteDelay = (mLastWriteTime+BATTERY_STATS_TIME)-now;
if (nextWriteDelay < nextCpuDelay) {
nextCpuDelay = nextWriteDelay;
}
if (nextCpuDelay > 0) {
mProcessCpuMutexFree.set(true);
this.wait(nextCpuDelay);
}
}
} catch (InterruptedException e) {
}
updateCpuStatsNow(); //更新CPU狀態(tài)
} catch (Exception e) {
}
}
}
};
...
}
首先，創(chuàng)建了一個名為“ActivityManager”的消息循環(huán)線程，不斷地接收其他進程發(fā)給AMS的消息；并把該消息循環(huán)線程與MainHandler綁定，這樣，由MainHandler完成消息的具體處理。
然后，創(chuàng)建了一些服務(wù)，并在/data/system目錄下創(chuàng)建該服務(wù)需要的文件或文件夾，具體如下：
| 服務(wù) | 服務(wù)說明 | 文件 | 文件說明 |
|---|---|---|---|
| BatteryStatsService | 電池狀態(tài)管理 | /data/system/batterystats.bin | 記錄包括電壓在內(nèi)的各種電池信息 |
| ProcessStatsService | 進程狀態(tài)管理 | /data/system/procstats | 記錄各個進程的狀態(tài)信息 |
| AppOpsService | 應(yīng)用操作權(quán)限管理 | /data/system/appops.xml | 存儲各個app的權(quán)限設(shè)置和操作信息 |
1.2.2 ActivityManagerService.setSystemProcess
首先，向SystemServiceManager中添加了若干個服務(wù)：
| 服務(wù) | 服務(wù)說明 |
|---|---|
| activity | AMS服務(wù)本身 |
| procstats | 進程狀態(tài)管理 |
| meminfo | 獲取內(nèi)存信息 |
| gfxinfo | 監(jiān)控分析GPU profiling信息 |
| dbinfo | 數(shù)據(jù)庫相關(guān)服務(wù) |
| cpuinfo | 獲取cpu相關(guān)信息 |
| permission | 權(quán)限控制相關(guān)服務(wù) |
然后，調(diào)用PMS的getApplicationInfo接口，獲取名為”android”的應(yīng)用程序信息。包名為”android”的apk即/system/framework/framework-res.apk，里面保存著系統(tǒng)GUI美化的相關(guān)文件，包括圖標，彈出對話框的樣式，動作特效，界面布局等。調(diào)用installSystemApplicationInfo加載framework-res.apk文件。
接著，調(diào)用newProcessRecordLocked新建一個ProcessRecord 對象app。ProcessRecord用來描述一個進程的所有信息，包括該進程的所有activity和service等。在這里就是system_server（AMS就是在system_server進程中運行的）。創(chuàng)建后，對app的一些成員變量進行初始化，包括設(shè)置為常駐內(nèi)存運行；設(shè)置system_server的pid等。
最后，調(diào)用mProcessNames.put()將創(chuàng)建的ProcessRecord 對象app加入到ProcessMap< ProcessRecord >類型的成員變量mProcessNames中。這里，app.processName=“system”。
這樣，AMS就得到了system_server的ProcessRecord，以后AMS也可以管理system_server了。
二、startOtherServices( )
2.1 systemServer觸發(fā)的AMS準備工作：
private void startOtherServices() {
...
//移除非系統(tǒng)的provider,安裝所有的系統(tǒng)provider,創(chuàng)建核心Settings Observer，用于監(jiān)控Settings的改變。
mActivityManagerService.installSystemProviders();
…
//保存WMS對象
mActivityManagerService.setWindowManager(wm);
…
//系統(tǒng)啟動前的準備工作，啟動SystemUI和Home界面等
mActivityManagerService.systemReady(new Runnable() {...});
}
2.2 mActivityManagerService.systemReady()
主要分三個階段來講：
public void systemReady(final Runnable goingCallback) {
before goingCallback.run()
goingCallback.run()
after goingCallback.run()
}
2.2.1 before goingCallback.run()
public void systemReady(final Runnable goingCallback){
if (mSystemReady) {//首次為false，不進入
if (goingCallback != null) {
goingCallback.run();
}
return;
}
mLocalDeviceIdleController = LocalServices.getService(DeviceIdleController.LocalService.class);
//用戶管理、最近任務(wù)、應(yīng)用程序操作權(quán)限管理相關(guān)驗證和準備工作。
mUserController.onSystemReady();
mRecentTasks.onSystemReadyLocked();
mAppOpsService.systemReady();
mSystemReady = true; //完成之后mSystemReady置為true
}
ArrayList<ProcessRecord> procsToKill = null;
synchronized(mPidsSelfLocked) {
for (int i=mPidsSelfLocked.size()-1; i>=0; i--) {
ProcessRecord proc = mPidsSelfLocked.valueAt(i);
//非persistent進程,加入procsToKill
if (!isAllowedWhileBooting(proc.info)){
if (procsToKill == null) {
procsToKill = new ArrayList<ProcessRecord>();
}
procsToKill.add(proc);
}
}
}
//殺掉procsToKill中的進程, 殺掉進程且不允許重啟
synchronized(this) {
if (procsToKill != null) {
for (int i=procsToKill.size()-1; i>=0; i--) {
ProcessRecord proc = procsToKill.get(i);
Slog.i(TAG, "Removing system update proc: " + proc);
removeProcessLocked(proc, true, false, "system update done");
}
}
mProcessesReady = true; //已經(jīng)為啟動進程做好準備
}
Slog.i(TAG, "System now ready");
EventLog.writeEvent(EventLogTags.BOOT_PROGRESS_AMS_READY,
SystemClock.uptimeMillis());
...
}
retrieveSettings();
final int currentUserId;
synchronized (this) {
currentUserId = mUserController.getCurrentUserIdLocked();
readGrantedUriPermissionsLocked();
}
}
此階段主要工作總結(jié)：
- 在當前運行的進程中，查找在systemReady之前不允許啟動的進程，然后調(diào)用removeProcessLocked()終止該進程并釋放資源。
- 讓系統(tǒng)和進程都處于ready狀態(tài) 即：
mSystemReady = true;
mProcessesReady = true;
關(guān)于mProcessesReady的解讀：
startProcessLocked()過程對于非persistent進程必須等待mProcessesReady = true才會真正創(chuàng)建進程，否則進程放入mProcessesOnHold隊列。 由此可見，mProcessesReady為沒有處于ready狀態(tài)之前則基本沒有其他進程。
2.2.2 goingCallback.run()
if (goingCallback != null) goingCallback.run();
這部分是回調(diào)到systemServer startOtherServices中完成的：
private void startOtherServices() {
mActivityManagerService.systemReady(new Runnable() {
@Override
public void run() {
Slog.i(TAG, "Making services ready");
mSystemServiceManager.startBootPhase(
SystemService.PHASE_ACTIVITY_MANAGER_READY);
Trace.traceBegin(Trace.TRACE_TAG_SYSTEM_SERVER, "PhaseActivityManagerReady");
Trace.traceBegin(Trace.TRACE_TAG_SYSTEM_SERVER, "StartObservingNativeCrashes");
try {
mActivityManagerService.startObservingNativeCrashes();
} catch (Throwable e) {
reportWtf("observing native crashes", e);
}
Trace.traceEnd(Trace.TRACE_TAG_SYSTEM_SERVER);
if (!mOnlyCore) {
Slog.i(TAG, "WebViewFactory preparation");
Trace.traceBegin(Trace.TRACE_TAG_SYSTEM_SERVER, "WebViewFactoryPreparation");
mWebViewUpdateService.prepareWebViewInSystemServer();
Trace.traceEnd(Trace.TRACE_TAG_SYSTEM_SERVER);
}
Trace.traceBegin(Trace.TRACE_TAG_SYSTEM_SERVER, "StartSystemUI");
try {
startSystemUi(context);
} catch (Throwable e) {
reportWtf("starting System UI", e);
}
Trace.traceEnd(Trace.TRACE_TAG_SYSTEM_SERVER);
Trace.traceBegin(Trace.TRACE_TAG_SYSTEM_SERVER, "MakeNetworkScoreReady");
try {
if (networkScoreF != null) networkScoreF.systemReady();
} catch (Throwable e) {
reportWtf("making Network Score Service ready", e);
}
Trace.traceEnd(Trace.TRACE_TAG_SYSTEM_SERVER);
Trace.traceBegin(Trace.TRACE_TAG_SYSTEM_SERVER, "MakeNetworkManagementServiceReady");
try {
if (networkManagementF != null) networkManagementF.systemReady();
} catch (Throwable e) {
reportWtf("making Network Managment Service ready", e);
}
Trace.traceEnd(Trace.TRACE_TAG_SYSTEM_SERVER);
Trace.traceBegin(Trace.TRACE_TAG_SYSTEM_SERVER, "MakeNetworkStatsServiceReady");
try {
if (networkStatsF != null) networkStatsF.systemReady();
} catch (Throwable e) {
reportWtf("making Network Stats Service ready", e);
}
Trace.traceEnd(Trace.TRACE_TAG_SYSTEM_SERVER);
Trace.traceBegin(Trace.TRACE_TAG_SYSTEM_SERVER, "MakeNetworkPolicyServiceReady");
try {
if (networkPolicyF != null) networkPolicyF.systemReady();
} catch (Throwable e) {
reportWtf("making Network Policy Service ready", e);
}
Trace.traceEnd(Trace.TRACE_TAG_SYSTEM_SERVER);
Trace.traceBegin(Trace.TRACE_TAG_SYSTEM_SERVER, "MakeConnectivityServiceReady");
try {
if (connectivityF != null) connectivityF.systemReady();
} catch (Throwable e) {
reportWtf("making Connectivity Service ready", e);
}
Trace.traceEnd(Trace.TRACE_TAG_SYSTEM_SERVER);
Watchdog.getInstance().start();
// It is now okay to let the various system services start their
// third party code...
Trace.traceEnd(Trace.TRACE_TAG_SYSTEM_SERVER);
Trace.traceBegin(Trace.TRACE_TAG_SYSTEM_SERVER, "PhaseThirdPartyAppsCanStart");
mSystemServiceManager.startBootPhase(
SystemService.PHASE_THIRD_PARTY_APPS_CAN_START);
try {
if (locationF != null) locationF.systemRunning();
} catch (Throwable e) {
reportWtf("Notifying Location Service running", e);
}
try {
if (countryDetectorF != null) countryDetectorF.systemRunning();
} catch (Throwable e) {
reportWtf("Notifying CountryDetectorService running", e);
}
try {
if (networkTimeUpdaterF != null) networkTimeUpdaterF.systemRunning();
} catch (Throwable e) {
reportWtf("Notifying NetworkTimeService running", e);
}
try {
if (commonTimeMgmtServiceF != null) {
commonTimeMgmtServiceF.systemRunning();
}
} catch (Throwable e) {
reportWtf("Notifying CommonTimeManagementService running", e);
}
try {
if (atlasF != null) atlasF.systemRunning();
} catch (Throwable e) {
reportWtf("Notifying AssetAtlasService running", e);
}
try {
// TODO(BT) Pass parameter to input manager
if (inputManagerF != null) inputManagerF.systemRunning();
} catch (Throwable e) {
reportWtf("Notifying InputManagerService running", e);
}
try {
if (telephonyRegistryF != null) telephonyRegistryF.systemRunning();
} catch (Throwable e) {
reportWtf("Notifying TelephonyRegistry running", e);
}
try {
if (mediaRouterF != null) mediaRouterF.systemRunning();
} catch (Throwable e) {
reportWtf("Notifying MediaRouterService running", e);
}
try {
if (mmsServiceF != null) mmsServiceF.systemRunning();
} catch (Throwable e) {
reportWtf("Notifying MmsService running", e);
}
try {
if (networkScoreF != null) networkScoreF.systemRunning();
} catch (Throwable e) {
reportWtf("Notifying NetworkScoreService running", e);
}
Trace.traceEnd(Trace.TRACE_TAG_SYSTEM_SERVER);
}
});
}
}
此階段主要工作總結(jié)：
- startBootPhase：550（PHASE_ACTIVITY_MANAGER_READY），回調(diào)相應(yīng)onBootPhase()方法；
- 啟動WebView；
- 啟動systemui服務(wù)；
- startBootPhase：600（PHASE_THIRD_PARTY_APPS_CAN_START），回調(diào)相應(yīng)onBootPhase()方法；
- 執(zhí)行一系列服務(wù)的systemReady方法；
- 執(zhí)行一系列服務(wù)的systemRunning方法；
2.2.3 after goingCallback.run()
mSystemServiceManager.startUser(currentUserId);//回調(diào)所有SystemService的onStartUser()方法
public void systemReady(final Runnable goingCallback){
synchronized (this) {
//啟動persistent進程
startPersistentApps(PackageManager.MATCH_DIRECT_BOOT_AWARE);
// Start up initial activity.
mBooting = true;
// Enable home activity for system user, so that the system can always boot
if (UserManager.isSplitSystemUser()) {
ComponentName cName = new ComponentName(mContext, SystemUserHomeActivity.class);
try {
AppGlobals.getPackageManager().setComponentEnabledSetting(cName,
[PackageManager.COMPONENT_ENABLED_STATE_ENABLED](http://PackageManager.COMPONENT_ENABLED_STATE_ENABLED), 0,
UserHandle.USER_SYSTEM);
} catch (RemoteException e) {
throw e.rethrowAsRuntimeException();
}
}
//啟動桌面activity
startHomeActivityLocked(currentUserId, "systemReady");
try {
if (AppGlobals.getPackageManager().hasSystemUidErrors()) {
Slog.e(TAG, "UIDs on the system are inconsistent, you need to wipe your"
+ " data partition or your device will be unstable.");
mUiHandler.obtainMessage(SHOW_UID_ERROR_UI_MSG).sendToTarget();
}
} catch (RemoteException e) {
}
if (!Build.isBuildConsistent()) {
Slog.e(TAG, "Build fingerprint is not consistent, warning user");
mUiHandler.obtainMessage(SHOW_FINGERPRINT_ERROR_UI_MSG).sendToTarget();
}
long ident = Binder.clearCallingIdentity();
try {
//system發(fā)送廣播USER_STARTED
Intent intent = new Intent(Intent.ACTION_USER_STARTED);
intent.addFlags(Intent.FLAG_RECEIVER_REGISTERED_ONLY
| Intent.FLAG_RECEIVER_FOREGROUND);
intent.putExtra(Intent.EXTRA_USER_HANDLE, currentUserId);
broadcastIntentLocked(null, null, intent,
null, null, 0, null, null, null, AppOpsManager.OP_NONE,
null, false, false, MY_PID, Process.SYSTEM_UID,
currentUserId);
//system發(fā)送廣播USER_STARTING
intent = new Intent(Intent.ACTION_USER_STARTING);
intent.addFlags(Intent.FLAG_RECEIVER_REGISTERED_ONLY);
intent.putExtra(Intent.EXTRA_USER_HANDLE, currentUserId);
broadcastIntentLocked(null, null, intent,
null, new IIntentReceiver.Stub() {
@Override
public void performReceive(Intent intent, int resultCode, String data,
Bundle extras, boolean ordered, boolean sticky, int sendingUser)
throws RemoteException {
}
}, 0, null, null,
new String[] {INTERACT_ACROSS_USERS}, AppOpsManager.OP_NONE,
null, true, false, MY_PID, Process.SYSTEM_UID, UserHandle.USER_ALL);
} catch (Throwable t) {
Slog.wtf(TAG, "Failed sending first user broadcasts", t);
} finally {
Binder.restoreCallingIdentity(ident);
}
mStackSupervisor.resumeFocusedStackTopActivityLocked();
mUserController.sendUserSwitchBroadcastsLocked(-1, currentUserId);
}
}
此階段主要工作總結(jié)：
- 回調(diào)所有SystemService的onStartUser()方法；
- 啟動persistent進程；
- 啟動home Activity;
- 發(fā)送廣播USER_STARTED和USER_STARTING；
- 發(fā)送廣播USER_SWITCHED；
最后畫了個簡單時序圖總結(jié)下AMS啟動流程：
參考：
https://blog.csdn.net/u010753159/article/details/51581113
http://gityuan.com/2016/02/21/activity-manager-service/
系列文章：
Android系統(tǒng)啟動（一）-開篇
Android系統(tǒng)啟動（二）-Init篇
Android系統(tǒng)啟動（三）-Zygote篇
Android系統(tǒng)啟動（四）-SystemServer篇
Android系統(tǒng)啟動（五）-ActivityManagerService篇
Android系統(tǒng)啟動（六）-Launcher篇
