Android系统启动-SystemServer下篇
2016-06-18 14:36
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Android系统启动-SystemServer下篇
2016-05-31 15:43 18人阅读 评论(0) 收藏 举报
分类：
Services/Binder/Callbacks学习（3）
目录(?)[+]
转自：http://gityuan.com/2016/02/20/Android-system-server-2/
基于Android 6.0的源码剖析， 分析Android启动过程的system_server进程
<code class="hljs cs" style="display: block; padding: 0.5em; color: rgb(0, 0, 0); background: rgb(255, 255, 255);">frameworks/<span class="hljs-keyword" style="color: rgb(0, 0, 136);">base</span>/core/java/android/app/ActivityThread.java frameworks/<span class="hljs-keyword" style="color: rgb(0, 0, 136);">base</span>/core/java/android/app/LoadedApk.java frameworks/<span class="hljs-keyword" style="color: rgb(0, 0, 136);">base</span>/core/java/android/app/ContextImpl.java frameworks/<span class="hljs-keyword" style="color: rgb(0, 0, 136);">base</span>/core/java/com/android/server/LocalServices.java frameworks/<span class="hljs-keyword" style="color: rgb(0, 0, 136);">base</span>/services/java/com/android/server/SystemServer.java frameworks/<span class="hljs-keyword" style="color: rgb(0, 0, 136);">base</span>/services/core/java/com/android/server/SystemServiceManager.java frameworks/<span class="hljs-keyword" style="color: rgb(0, 0, 136);">base</span>/services/core/java/com/android/server/ServiceThread.java frameworks/<span class="hljs-keyword" style="color: rgb(0, 0, 136);">base</span>/services/core/java/com/android/server/pm/Installer.java frameworks/<span class="hljs-keyword" style="color: rgb(0, 0, 136);">base</span>/services/core/java/com/android/server/am/ActivityManagerService.java </code>
一、启动调用栈
System_server启动函数调用类的栈关系：<code class="hljs css" style="display: block; padding: 0.5em; color: rgb(0, 0, 0); background: rgb(255, 255, 255);"><span class="hljs-selector-tag">SystemServer</span><span class="hljs-selector-class">.main</span> <span class="hljs-selector-tag">SystemServer</span><span class="hljs-selector-class">.run</span> <span class="hljs-selector-tag">createSystemContext</span> <span class="hljs-selector-tag">ActivityThread</span><span class="hljs-selector-class">.systemMain</span> <span class="hljs-selector-tag">ActivityThread</span><span class="hljs-selector-class">.attach</span> <span class="hljs-selector-tag">LoadedApk</span><span class="hljs-selector-class">.makeApplication</span> <span class="hljs-selector-tag">ActivityThread</span><span class="hljs-selector-class">.getSystemContext</span> <span class="hljs-selector-tag">ContextImpl</span><span class="hljs-selector-class">.createSystemContext</span> <span class="hljs-selector-tag">startBootstrapServices</span>(); <span class="hljs-selector-tag">startCoreServices</span>(); <span class="hljs-selector-tag">startOtherServices</span>(); <span class="hljs-selector-tag">Looper</span><span class="hljs-selector-class">.loop</span>(); </code>
二、 SystemServer分析
上一篇文章Android系统启动-systemServer上篇讲解了从Zygote一路启动到SystemServer的过程，本文重要是讲述system_server所承载的java framework的系统服务框架，是如何一路路启动的。Step 1. SystemServer.main
<code class="hljs java" style="display: block; padding: 0.5em; color: rgb(0, 0, 0); background: rgb(255, 255, 255);"><span class="hljs-function"><span class="hljs-keyword" style="color: rgb(0, 0, 136);">public</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136);">static</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136);">void</span> <span class="hljs-title">main</span><span class="hljs-params" style="color: rgb(102, 0, 102);">(String[] args)</span> </span>{
<span class="hljs-comment" style="color: rgb(136, 0, 0);">//先初始化SystemServer对象，再调用对象的run()方法， 【见Step 2】</span>
<span class="hljs-keyword" style="color: rgb(0, 0, 136);">new</span> SystemServer().run();
}
</code>Step 2. SystemServer.run
<code class="hljs java" style="display: block; padding: 0.5em; color: rgb(0, 0, 0); background: rgb(255, 255, 255);"><span class="hljs-function"><span class="hljs-keyword" style="color: rgb(0, 0, 136);">private</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136);">void</span> <span class="hljs-title">run</span><span class="hljs-params" style="color: rgb(102, 0, 102);">()</span> </span>{
<span class="hljs-comment" style="color: rgb(136, 0, 0);">//当系统时间比1970年更早，就设置当前系统时间为1970年</span>
<span class="hljs-keyword" style="color: rgb(0, 0, 136);">if</span> (System.currentTimeMillis() < EARLIEST_SUPPORTED_TIME) {
SystemClock.setCurrentTimeMillis(EARLIEST_SUPPORTED_TIME);
}
<span class="hljs-comment" style="color: rgb(136, 0, 0);">//变更虚拟机的库文件，对于Android 6.0默认采用的是libart.so</span>
SystemProperties.set(<span class="hljs-string" style="color: rgb(0, 136, 0);">"persist.sys.dalvik.vm.lib.2"</span>, VMRuntime.getRuntime().vmLibrary());
<span class="hljs-comment" style="color: rgb(136, 0, 0);">//isEnabled()为true，则开启采用分析器</span>
<span class="hljs-keyword" style="color: rgb(0, 0, 136);">if</span> (SamplingProfilerIntegration.isEnabled()) {
SamplingProfilerIntegration.start();
mProfilerSnapshotTimer = <span class="hljs-keyword" style="color: rgb(0, 0, 136);">new</span> Timer();
<span class="hljs-comment" style="color: rgb(136, 0, 0);">//system_server每隔1小时采用一次，并保存结果到system_server文件</span>
mProfilerSnapshotTimer.schedule(<span class="hljs-keyword" style="color: rgb(0, 0, 136);">new</span> TimerTask() {
<span class="hljs-meta">@Override</span>
<span class="hljs-function"><span class="hljs-keyword" style="color: rgb(0, 0, 136);">public</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136);">void</span> <span class="hljs-title">run</span><span class="hljs-params" style="color: rgb(102, 0, 102);">()</span> </span>{
SamplingProfilerIntegration.writeSnapshot(<span class="hljs-string" style="color: rgb(0, 136, 0);">"system_server"</span>, <span class="hljs-keyword" style="color: rgb(0, 0, 136);">null</span>);
}
}, SNAPSHOT_INTERVAL, SNAPSHOT_INTERVAL);
}
<span class="hljs-comment" style="color: rgb(136, 0, 0);">//清除vm内存增长上限，由于启动过程需要较多的虚拟机内存空间</span>
VMRuntime.getRuntime().clearGrowthLimit();
<span class="hljs-comment" style="color: rgb(136, 0, 0);">//设置内存的可能有效使用率为0.8</span>
VMRuntime.getRuntime().setTargetHeapUtilization(<span class="hljs-number" style="color: rgb(0, 102, 102);">0.8f</span>);
<span class="hljs-comment" style="color: rgb(136, 0, 0);">// 针对部分设备依赖于运行时就产生指纹信息，因此需要在开机完成前已经定义</span>
Build.ensureFingerprintProperty();
<span class="hljs-comment" style="color: rgb(136, 0, 0);">//访问环境变量前，需要明确地指定用户</span>
Environment.setUserRequired(<span class="hljs-keyword" style="color: rgb(0, 0, 136);">true</span>);
<span class="hljs-comment" style="color: rgb(136, 0, 0);">//确保当前系统进程的binder调用，总是运行在前台优先级(foreground priority)</span>
BinderInternal.disableBackgroundScheduling(<span class="hljs-keyword" style="color: rgb(0, 0, 136);">true</span>);
android.os.Process.setThreadPriority(android.os.Process.THREAD_PRIORITY_FOREGROUND);
android.os.Process.setCanSelfBackground(<span class="hljs-keyword" style="color: rgb(0, 0, 136);">false</span>);
<span class="hljs-comment" style="color: rgb(136, 0, 0);">// 主线程looper就在当前线程运行</span>
Looper.prepareMainLooper();
<span class="hljs-comment" style="color: rgb(136, 0, 0);">//加载android_servers.so库，该库包含的源码在frameworks/base/services/目录下</span>
System.loadLibrary(<span class="hljs-string" style="color: rgb(0, 136, 0);">"android_servers"</span>);
<span class="hljs-comment" style="color: rgb(136, 0, 0);">//检测上次关机过程是否失败，该方法可能不会返回</span>
performPendingShutdown();
<span class="hljs-comment" style="color: rgb(136, 0, 0);">//初始化系统上下文 【见Step 3】</span>
createSystemContext();
<span class="hljs-comment" style="color: rgb(136, 0, 0);">//创建系统服务管理</span>
mSystemServiceManager = <span class="hljs-keyword" style="color: rgb(0, 0, 136);">new</span> SystemServiceManager(mSystemContext);
<span class="hljs-comment" style="color: rgb(136, 0, 0);">//将mSystemServiceManager添加到本地服务的成员sLocalServiceObjects</span>
LocalServices.addService(SystemServiceManager.class, mSystemServiceManager);
<span class="hljs-comment" style="color: rgb(136, 0, 0);">//启动各种系统服务</span>
<span class="hljs-keyword" style="color: rgb(0, 0, 136);">try</span> {
startBootstrapServices(); <span class="hljs-comment" style="color: rgb(136, 0, 0);">// 启动引导服务【见Step 4】</span>
startCoreServices(); <span class="hljs-comment" style="color: rgb(136, 0, 0);">// 启动核心服务【见Step 5】</span>
startOtherServices(); <span class="hljs-comment" style="color: rgb(136, 0, 0);">// 启动其他服务【见Step 6】</span>
} <span class="hljs-keyword" style="color: rgb(0, 0, 136);">catch</span> (Throwable ex) {
Slog.e(<span class="hljs-string" style="color: rgb(0, 136, 0);">"System"</span>, <span class="hljs-string" style="color: rgb(0, 136, 0);">"************ Failure starting system services"</span>, ex);
<span class="hljs-keyword" style="color: rgb(0, 0, 136);">throw</span> ex;
}
<span class="hljs-comment" style="color: rgb(136, 0, 0);">//用于debug版本，将log事件不断循环地输出到dropbox（用于分析）</span>
<span class="hljs-keyword" style="color: rgb(0, 0, 136);">if</span> (StrictMode.conditionallyEnableDebugLogging()) {
Slog.i(TAG, <span class="hljs-string" style="color: rgb(0, 136, 0);">"Enabled StrictMode for system server main thread."</span>);
}
<span class="hljs-comment" style="color: rgb(136, 0, 0);">//一直循环执行</span>
Looper.loop();
<span class="hljs-keyword" style="color: rgb(0, 0, 136);">throw</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136);">new</span> RuntimeException(<span class="hljs-string" style="color: rgb(0, 136, 0);">"Main thread loop unexpectedly exited"</span>);
}
</code>LocalServices通过用静态Map变量sLocalServiceObjects，来保存以服务类名为key，以具体服务对象为value的Map结构。
Step 3. SystemServer.createSystemContext
<code class="hljs java" style="display: block; padding: 0.5em; color: rgb(0, 0, 0); background: rgb(255, 255, 255);"><span class="hljs-function"><span class="hljs-keyword" style="color: rgb(0, 0, 136);">private</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136);">void</span> <span class="hljs-title">createSystemContext</span><span class="hljs-params" style="color: rgb(102, 0, 102);">()</span> </span>{
<span class="hljs-comment" style="color: rgb(136, 0, 0);">//创建ActivityThread对象【见Step 3-1】</span>
ActivityThread activityThread = ActivityThread.systemMain();
<span class="hljs-comment" style="color: rgb(136, 0, 0);">//创建ContextImpl、LoadedApk对象【见Step 3-2】</span>
mSystemContext = activityThread.getSystemContext();
<span class="hljs-comment" style="color: rgb(136, 0, 0);">//设置主题</span>
mSystemContext.setTheme(android.R.style.Theme_DeviceDefault_Light_DarkActionBar);
}
</code>Step 3-1. ActivityThread.systemMain
<code class="hljs java" style="display: block; padding: 0.5em; color: rgb(0, 0, 0); background: rgb(255, 255, 255);"><span class="hljs-function"><span class="hljs-keyword" style="color: rgb(0, 0, 136);">public</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136);">static</span> ActivityThread <span class="hljs-title">systemMain</span><span class="hljs-params" style="color: rgb(102, 0, 102);">()</span> </span>{
<span class="hljs-comment" style="color: rgb(136, 0, 0);">//对于低内存的设备，禁用硬件加速</span>
<span class="hljs-keyword" style="color: rgb(0, 0, 136);">if</span> (!ActivityManager.isHighEndGfx()) {
HardwareRenderer.disable(<span class="hljs-keyword" style="color: rgb(0, 0, 136);">true</span>);
} <span class="hljs-keyword" style="color: rgb(0, 0, 136);">else</span> {
HardwareRenderer.enableForegroundTrimming();
}
<span class="hljs-comment" style="color: rgb(136, 0, 0);">// 创建ActivityThread</span>
ActivityThread thread = <span class="hljs-keyword" style="color: rgb(0, 0, 136);">new</span> ActivityThread();
<span class="hljs-comment" style="color: rgb(136, 0, 0);">// 创建Application以及调用其onCreate()方法【见Step 3-1-1】</span>
thread.attach(<span class="hljs-keyword" style="color: rgb(0, 0, 136);">true</span>);
<span class="hljs-keyword" style="color: rgb(0, 0, 136);">return</span> thread;
}
</code>Step 3-1-1. ActivityThread.attach
<code class="hljs java" style="display: block; padding: 0.5em; color: rgb(0, 0, 0); background: rgb(255, 255, 255);"><span class="hljs-function"><span class="hljs-keyword" style="color: rgb(0, 0, 136);">private</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136);">void</span> <span class="hljs-title">attach</span><span class="hljs-params" style="color: rgb(102, 0, 102);">(<span class="hljs-keyword" style="color: rgb(0, 0, 136);">boolean</span> system)</span> </span>{
sCurrentActivityThread = <span class="hljs-keyword" style="color: rgb(0, 0, 136);">this</span>;
mSystemThread = system;
<span class="hljs-keyword" style="color: rgb(0, 0, 136);">if</span> (!system) {
...
} <span class="hljs-keyword" style="color: rgb(0, 0, 136);">else</span> {
<span class="hljs-comment" style="color: rgb(136, 0, 0);">//system=true,进入此分支</span>
android.ddm.DdmHandleAppName.setAppName(<span class="hljs-string" style="color: rgb(0, 136, 0);">"system_process"</span>,
UserHandle.myUserId());
<span class="hljs-keyword" style="color: rgb(0, 0, 136);">try</span> {
mInstrumentation = <span class="hljs-keyword" style="color: rgb(0, 0, 136);">new</span> Instrumentation();
<span class="hljs-comment" style="color: rgb(136, 0, 0);">// 创建应用上下文</span>
ContextImpl context = ContextImpl.createAppContext(
<span class="hljs-keyword" style="color: rgb(0, 0, 136);">this</span>, getSystemContext().mPackageInfo);
<span class="hljs-comment" style="color: rgb(136, 0, 0);">//创建Application 【见Step 3-1-1-1】</span>
mInitialApplication = context.mPackageInfo.makeApplication(<span class="hljs-keyword" style="color: rgb(0, 0, 136);">true</span>, <span class="hljs-keyword" style="color: rgb(0, 0, 136);">null</span>);
<span class="hljs-comment" style="color: rgb(136, 0, 0);">//调用Application.onCreate()方法</span>
mInitialApplication.onCreate();
} <span class="hljs-keyword" style="color: rgb(0, 0, 136);">catch</span> (Exception e) {
<span class="hljs-keyword" style="color: rgb(0, 0, 136);">throw</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136);">new</span> RuntimeException(
<span class="hljs-string" style="color: rgb(0, 136, 0);">"Unable to instantiate Application():"</span> + e.toString(), e);
}
}
<span class="hljs-comment" style="color: rgb(136, 0, 0);">//添加dropbox log信息到libcore</span>
DropBox.setReporter(<span class="hljs-keyword" style="color: rgb(0, 0, 136);">new</span> DropBoxReporter());
<span class="hljs-comment" style="color: rgb(136, 0, 0);">// 设置回调方法</span>
ViewRootImpl.addConfigCallback(<span class="hljs-keyword" style="color: rgb(0, 0, 136);">new</span> ComponentCallbacks2() {
<span class="hljs-meta">@Override</span>
<span class="hljs-function"><span class="hljs-keyword" style="color: rgb(0, 0, 136);">public</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136);">void</span> <span class="hljs-title">onConfigurationChanged</span><span class="hljs-params" style="color: rgb(102, 0, 102);">(Configuration newConfig)</span> </span>{
<span class="hljs-keyword" style="color: rgb(0, 0, 136);">synchronized</span> (mResourcesManager) {
<span class="hljs-keyword" style="color: rgb(0, 0, 136);">if</span> (mResourcesManager.applyConfigurationToResourcesLocked(newConfig, <span class="hljs-keyword" style="color: rgb(0, 0, 136);">null</span>)) {
<span class="hljs-keyword" style="color: rgb(0, 0, 136);">if</span> (mPendingConfiguration == <span class="hljs-keyword" style="color: rgb(0, 0, 136);">null</span> ||
mPendingConfiguration.isOtherSeqNewer(newConfig)) {
mPendingConfiguration = newConfig;
sendMessage(H.CONFIGURATION_CHANGED, newConfig);
}
}
}
}
<span class="hljs-meta">@Override</span>
<span class="hljs-function"><span class="hljs-keyword" style="color: rgb(0, 0, 136);">public</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136);">void</span> <span class="hljs-title">onLowMemory</span><span class="hljs-params" style="color: rgb(102, 0, 102);">()</span> </span>{
}
<span class="hljs-meta">@Override</span>
<span class="hljs-function"><span class="hljs-keyword" style="color: rgb(0, 0, 136);">public</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136);">void</span> <span class="hljs-title">onTrimMemory</span><span class="hljs-params" style="color: rgb(102, 0, 102);">(<span class="hljs-keyword" style="color: rgb(0, 0, 136);">int</span> level)</span> </span>{
}
});
}
</code>主要工作是创建应用上下文ContextImpl，创建Application以及调用其onCreate()方法，设置DropBox以及ComponentCallbacks2回调方法。
Step 3-1-1-1. LoadedApk.makeApplication
<code class="hljs java" style="display: block; padding: 0.5em; color: rgb(0, 0, 0); background: rgb(255, 255, 255);"><span class="hljs-function"><span class="hljs-keyword" style="color: rgb(0, 0, 136);">public</span> Application <span class="hljs-title">makeApplication</span><span class="hljs-params" style="color: rgb(102, 0, 102);">(<span class="hljs-keyword" style="color: rgb(0, 0, 136);">boolean</span> forceDefaultAppClass,
Instrumentation instrumentation)</span> </span>{
<span class="hljs-keyword" style="color: rgb(0, 0, 136);">if</span> (mApplication != <span class="hljs-keyword" style="color: rgb(0, 0, 136);">null</span>) {
<span class="hljs-keyword" style="color: rgb(0, 0, 136);">return</span> mApplication;
}
Application app = <span class="hljs-keyword" style="color: rgb(0, 0, 136);">null</span>;
String appClass = mApplicationInfo.className;
<span class="hljs-keyword" style="color: rgb(0, 0, 136);">if</span> (forceDefaultAppClass || (appClass == <span class="hljs-keyword" style="color: rgb(0, 0, 136);">null</span>)) {
appClass = <span class="hljs-string" style="color: rgb(0, 136, 0);">"android.app.Application"</span>; <span class="hljs-comment" style="color: rgb(136, 0, 0);">//设置class名</span>
}
<span class="hljs-keyword" style="color: rgb(0, 0, 136);">try</span> {
java.lang.ClassLoader cl = getClassLoader();
<span class="hljs-keyword" style="color: rgb(0, 0, 136);">if</span> (!mPackageName.equals(<span class="hljs-string" style="color: rgb(0, 136, 0);">"android"</span>)) {
initializeJavaContextClassLoader(); <span class="hljs-comment" style="color: rgb(136, 0, 0);">//不进入该分支</span>
}
ContextImpl appContext = ContextImpl.createAppContext(mActivityThread, <span class="hljs-keyword" style="color: rgb(0, 0, 136);">this</span>);
<span class="hljs-comment" style="color: rgb(136, 0, 0);">// 创建Application</span>
app = mActivityThread.mInstrumentation.newApplication(
cl, appClass, appContext);
appContext.setOuterContext(app);
} <span class="hljs-keyword" style="color: rgb(0, 0, 136);">catch</span> (Exception e) {
...
}
<span class="hljs-comment" style="color: rgb(136, 0, 0);">// 将前面创建的app添加到应用列表。</span>
mActivityThread.mAllApplications.add(app);
mApplication = app;
...
<span class="hljs-keyword" style="color: rgb(0, 0, 136);">return</span> app;
}
</code>在该方法调用之前，已经创建了LoadedApk对象，该对象的成员变量mPackageName=”android”; mClassLoader = ClassLoader.getSystemClassLoader();
Step 3-2. ActivityThread.getSystemContext
<code class="hljs java" style="display: block; padding: 0.5em; color: rgb(0, 0, 0); background: rgb(255, 255, 255);"><span class="hljs-function"><span class="hljs-keyword" style="color: rgb(0, 0, 136);">public</span> ContextImpl <span class="hljs-title">getSystemContext</span><span class="hljs-params" style="color: rgb(102, 0, 102);">()</span> </span>{
<span class="hljs-keyword" style="color: rgb(0, 0, 136);">synchronized</span> (<span class="hljs-keyword" style="color: rgb(0, 0, 136);">this</span>) {
<span class="hljs-keyword" style="color: rgb(0, 0, 136);">if</span> (mSystemContext == <span class="hljs-keyword" style="color: rgb(0, 0, 136);">null</span>) {
<span class="hljs-comment" style="color: rgb(136, 0, 0);">//创建ContextImpl对象【见Step 3-2-1】</span>
mSystemContext = ContextImpl.createSystemContext(<span class="hljs-keyword" style="color: rgb(0, 0, 136);">this</span>);
}
<span class="hljs-keyword" style="color: rgb(0, 0, 136);">return</span> mSystemContext;
}
}
</code>Step 3-2-1. ContextImpl.createSystemContext
<code class="hljs java" style="display: block; padding: 0.5em; color: rgb(0, 0, 0); background: rgb(255, 255, 255);"><span class="hljs-function"><span class="hljs-keyword" style="color: rgb(0, 0, 136);">static</span> ContextImpl <span class="hljs-title">createSystemContext</span><span class="hljs-params" style="color: rgb(102, 0, 102);">(ActivityThread mainThread)</span> </span>{
<span class="hljs-comment" style="color: rgb(136, 0, 0);">//创建LoadedApk对象</span>
LoadedApk packageInfo = <span class="hljs-keyword" style="color: rgb(0, 0, 136);">new</span> LoadedApk(mainThread);
<span class="hljs-comment" style="color: rgb(136, 0, 0);">//创建ContextImpl对象</span>
ContextImpl context = <span class="hljs-keyword" style="color: rgb(0, 0, 136);">new</span> ContextImpl(<span class="hljs-keyword" style="color: rgb(0, 0, 136);">null</span>, mainThread,
packageInfo, <span class="hljs-keyword" style="color: rgb(0, 0, 136);">null</span>, <span class="hljs-keyword" style="color: rgb(0, 0, 136);">null</span>, <span class="hljs-keyword" style="color: rgb(0, 0, 136);">false</span>, <span class="hljs-keyword" style="color: rgb(0, 0, 136);">null</span>, <span class="hljs-keyword" style="color: rgb(0, 0, 136);">null</span>, Display.INVALID_DISPLAY);
context.mResources.updateConfiguration(context.mResourcesManager.getConfiguration(),
context.mResourcesManager.getDisplayMetricsLocked());
<span class="hljs-keyword" style="color: rgb(0, 0, 136);">return</span> context;
}
</code>运行到这里，system_server的准备环境基本完成，接下来开始system_server中最为核心的过程，启动系统服务。通过
startBootstrapServices(),
startCoreServices(),
startOtherServices()3个方法。
Step 4. startBootstrapServices
[–>SystemServer.java]
<code class="hljs cpp" style="display: block; padding: 0.5em; color: rgb(0, 0, 0); background: rgb(255, 255, 255);"><span class="hljs-function"><span class="hljs-keyword" style="color: rgb(0, 0, 136);">private</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136);">void</span> <span class="hljs-title">startBootstrapServices</span><span class="hljs-params" style="color: rgb(102, 0, 102);">()</span> </span>{
<span class="hljs-comment" style="color: rgb(136, 0, 0);">//阻塞等待与installd建立socket通道</span>
Installer installer = mSystemServiceManager.startService(Installer.class);
<span class="hljs-comment" style="color: rgb(136, 0, 0);">//启动服务ActivityManagerService</span>
mActivityManagerService = mSystemServiceManager.startService(
ActivityManagerService.Lifecycle.class).getService();
mActivityManagerService.setSystemServiceManager(mSystemServiceManager);
mActivityManagerService.setInstaller(installer);
<span class="hljs-comment" style="color: rgb(136, 0, 0);">//启动服务PowerManagerService</span>
mPowerManagerService = mSystemServiceManager.startService(PowerManagerService.class);
<span class="hljs-comment" style="color: rgb(136, 0, 0);">//初始化power management</span>
mActivityManagerService.initPowerManagement();
<span class="hljs-comment" style="color: rgb(136, 0, 0);">//启动服务LightsService </span>
mSystemServiceManager.startService(LightsService.<span class="hljs-keyword" style="color: rgb(0, 0, 136);">class</span>);
<span class="hljs-comment" style="color: rgb(136, 0, 0);">//启动服务DisplayManagerService</span>
mDisplayManagerService = mSystemServiceManager.startService(DisplayManagerService.class);
<span class="hljs-comment" style="color: rgb(136, 0, 0);">//在初始化package manager之前，需要默认的显示</span>
mSystemServiceManager.startBootPhase(SystemService.PHASE_WAIT_FOR_DEFAULT_DISPLAY);
<span class="hljs-comment" style="color: rgb(136, 0, 0);">//当设备正在加密时，仅运行核心</span>
String cryptState = SystemProperties.get(<span class="hljs-string" style="color: rgb(0, 136, 0);">"vold.decrypt"</span>);
<span class="hljs-keyword" style="color: rgb(0, 0, 136);">if</span> (ENCRYPTING_STATE.equals(cryptState)) {
mOnlyCore = <span class="hljs-literal" style="color: rgb(0, 102, 102);">true</span>;
} <span class="hljs-keyword" style="color: rgb(0, 0, 136);">else</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136);">if</span> (ENCRYPTED_STATE.equals(cryptState)) {
mOnlyCore = <span class="hljs-literal" style="color: rgb(0, 102, 102);">true</span>;
}
<span class="hljs-comment" style="color: rgb(136, 0, 0);">//启动服务PackageManagerService</span>
mPackageManagerService = PackageManagerService.main(mSystemContext, installer,
mFactoryTestMode != FactoryTest.FACTORY_TEST_OFF, mOnlyCore);
mFirstBoot = mPackageManagerService.isFirstBoot();
mPackageManager = mSystemContext.getPackageManager();
<span class="hljs-comment" style="color: rgb(136, 0, 0);">//启动服务UserManagerService，新建目录/data/user/</span>
ServiceManager.addService(Context.USER_SERVICE, UserManagerService.getInstance());
AttributeCache.init(mSystemContext);
<span class="hljs-comment" style="color: rgb(136, 0, 0);">//设置AMS</span>
mActivityManagerService.setSystemProcess();
<span class="hljs-comment" style="color: rgb(136, 0, 0);">//启动传感器服务</span>
startSensorService();
}
</code>该方法所创建的服务：ActivityManagerService, PowerManagerService, LightsService, DisplayManagerService， PackageManagerService， UserManagerService， sensor服务.
Step 5. startCoreServices
<code class="hljs cpp" style="display: block; padding: 0.5em; color: rgb(0, 0, 0); background: rgb(255, 255, 255);"><span class="hljs-function"><span class="hljs-keyword" style="color: rgb(0, 0, 136);">private</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136);">void</span> <span class="hljs-title">startCoreServices</span><span class="hljs-params" style="color: rgb(102, 0, 102);">()</span> </span>{
<span class="hljs-comment" style="color: rgb(136, 0, 0);">//启动服务BatteryService，用于统计电池电量，需要LightService.</span>
mSystemServiceManager.startService(BatteryService.<span class="hljs-keyword" style="color: rgb(0, 0, 136);">class</span>);
<span class="hljs-comment" style="color: rgb(136, 0, 0);">//启动服务UsageStatsService，用于统计应用使用情况</span>
mSystemServiceManager.startService(UsageStatsService.<span class="hljs-keyword" style="color: rgb(0, 0, 136);">class</span>);
mActivityManagerService.setUsageStatsManager(
LocalServices.getService(UsageStatsManagerInternal.class));
mPackageManagerService.getUsageStatsIfNoPackageUsageInfo();
<span class="hljs-comment" style="color: rgb(136, 0, 0);">//启动服务WebViewUpdateService</span>
mSystemServiceManager.startService(WebViewUpdateService.<span class="hljs-keyword" style="color: rgb(0, 0, 136);">class</span>);
}
</code>启动服务BatteryService，UsageStatsService，WebViewUpdateService。
Step 6. startOtherServices
该方法比较长，有近千行代码，逻辑很简单，主要是启动一系列的服务，这里就不列举源码了，在第四节直接对其中的服务进行一个简单分类。
三、Service启动过程
接下来，开始正式进入启动系统服务的过程。启动方式
system_server进程中的服务启动方式有两种，一种是通过SystemServiceManager的
startService()，该方法用于启动继承于SystemService的服务。主要功能：创建serviceClass类的对象，将刚创建对象添加到SystemServiceManager的成员变量mServices，再调用刚创建对象的onStart()方法。对于服务启动到一定阶段，进入相应的Phase时，会调用SystemServiceManager的
startBootPhase()回调方法，该方法会循环遍历所有向
SystemServiceManager注册过的service的
onBootPhase()方法。
另一种是通过ServiceManager的
addService(String name, IBinder service)，该方法用于初始化继承于IBinder的服务。主要功能将该服务向Native层的service
Manager注册服务。
启动流程
SystemServiceManager的startBootPhase(）方法贯穿整个阶段，启动阶段从
PHASE_WAIT_FOR_DEFAULT_DISPLAY到
PHASE_BOOT_COMPLETED，如下图：
启动流程分析：
PHASE_WAIT_FOR_DEFAULT_DISPLAY=100，该阶段等待Display有默认显示;
PHASE_LOCK_SETTINGS_READY=480，进入该阶段服务能获取锁屏设置的数据;
PHASE_SYSTEM_SERVICES_READY=500，进入该阶段服务能安全地调用核心系统服务，如PMS;
PHASE_ACTIVITY_MANAGER_READY=550，进入该阶段服务能广播Intent;
PHASE_THIRD_PARTY_APPS_CAN_START=600，进入该阶段服务能start/bind第三方apps，app能通过BInder调用service;
PHASE_BOOT_COMPLETED=1000，该阶段是发生在Boot完成和home应用启动完毕。系统服务更倾向于监听该阶段，而不是注册广播ACTION_BOOT_COMPLETED，从而降低系统延迟。
Phase 100
创建ActivityManagerService、PowerManagerService、LightsService、DisplayManagerService共4项服务；
接着则进入阶段
100，该阶段调用DisplayManagerService的
onBootPhase()方法。
Phase 480&&500
创建PackageManagerService、WindowManagerService、InputManagerService、NetworkManagerService、DropBoxManagerService/FingerprintService等服务
接着则进入阶段
480，该阶段调用DevicePolicyManagerService的
onBootPhase()方法；紧接着进入阶段
500，实现该阶段的回调方法的服务较多。
Phase 550
WindowManagerService、PowerManagerService、PackageManagerService、DisplayManagerService分别依次执行
systemReady()方法；然后ActivityManagerService进入
systemReady()方法;
接着则进入阶段
550，实现该阶段的回调方法的服务较多。
Phase 600
AMS启动native crash监控,，加载WebView，启动SystemUi；然后是NetworkScoreService、NetworkManagementService、NetworkStatsService、NetworkPolicyManagerService、ConnectivityService、AudioService分别依次执行
systemReady()方法，然后是启动Watchdog。
接着则进入阶段
600，实现该阶段的回调方法的服务较多。
Phase 1000
WallpaperManagerService、InputMethodManagerService、LocationManagerService、CountryDetectorService、NetworkTimeUpdateService、CommonTimeManagementService、TextServicesManagerService、AssetAtlasService、InputManagerService、TelephonyRegistry、MediaRouterService、MmsServiceBroker这些服务依次执行其
systemRunning()方法。经过一定流程，当ActivityManagerServer进入
finishBooting()时，则启动流程进入阶段
PHASE_BOOT_COMPLETED=1000。
到此所有服务启动完成，system_server进程启动完成，则进入
Looper.loop()状态，随时待命，等待MessageQueue中的消息到来，则马上进入执行状态。
四、服务分类
system_server进程，从源码角度划分为引导服务、核心服务、其他服务3类。引导服务：ActivityManagerService、PowerManagerService、LightsService、DisplayManagerService、PackageManagerService、UserManagerService、SensorService共7项服务；
核心服务：BatteryService、UsageStatsService、WebViewUpdateService共3项服务；
其他服务：AlarmManagerService、VibratorService等共70多项服务
合计总大约80多个服务，下面只是简单地对所有服务分类（个人划分，便于后期分析）：
重量级服务：ActivityManagerService、PackageManagerService、WindowManagerService
功耗相关：PowerManagerService、BatteryService、BatteryStatsService、DreamManagerService
统计调度相关：DropBoxManagerService、SamplingProfilerService、UsageStatsService、DiskStatsService、SchedulingPolicyService、DeviceStorageMonitorService、AlarmManagerService、DeviceIdleController、DockObserver、ThermalObserver、JobSchedulerService、AccessibilityManagerService
UI相关：DisplayManagerService、LightsService、GraphicsStatsService、StatusBarManagerService、NotificationManagerService、WallpaperManagerService、UiModeManagerService、AppWidgetService、LauncherAppsService、TextServicesManagerService、ContentService、LockSettingsService、InputManagerService、InputMethodManagerServiceMountService、FingerprintService、TvInputManagerService
网络相关：NetworkManagementService、NetworkScoreService、NetworkStatsService、NetworkPolicyManagerService、ConnectivityService、BluetoothService、WifiP2pService、WifiService、WifiScanningService、EthernetService、WebViewUpdateService
Media相关：AudioService、MediaRouterService、VoiceInteractionManagerService、MediaProjectionManagerService、MediaSessionService、
设备相关：DevicePolicyManagerService、PrintManagerService、BackupManagerService、UserManagerService、AccountManagerService、TrustManagerService、SensorService、LocationManagerService、VibratorService、CountryDetectorService、GestureLauncherService、PersistentDataBlockService、ClipboardService
其他：TelephonyRegistry、TelecomLoaderService、NsdService、UpdateLockService、SerialService、SearchManagerService、CommonTimeManagementService、AssetAtlasService、ConsumerIrService、MidiServiceCameraService、TwilightService、RestrictionsManagerService、MmsServiceBroker、RttService、UsbService。
后续，会针对其中比较重要的服务进行展开详解。
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