1.前言
- 最近一直在看 《Android进阶解密》 的一本书，这本书编写逻辑、流程都非常好，而且很容易看懂，非常推荐大家去看看（没有收广告费，单纯觉得作者写的很好）。
- 上一篇简单的介绍了Android进阶（二）： 应用进程启动过程，最终知道了ActivityThread就是代表应用进程。
- 今天就介绍ActivityThread启动之后，是如何启动
Application （基于Android 8.0 系统）。
- 文章中实例 linhaojian的Github
2.Application启动过程的时序图
Application启动流程.png
3.源码分析
3.1 ActivityThread初始化：
public static void main(String[] args) {
//...
//创建ActivityThread对象 & 调用attach()
ActivityThread thread = new ActivityThread();
thread.attach(false, startSeq);
//创建主线程的Handler
if (sMainThreadHandler == null) {
sMainThreadHandler = thread.getHandler();
}
if (false) {
Looper.myLooper().setMessageLogging(new
LogPrinter(Log.DEBUG, "ActivityThread"));
}
// End of event ActivityThreadMain.
Trace.traceEnd(Trace.TRACE_TAG_ACTIVITY_MANAGER);
//创建主线程的Looper
Looper.loop();
}
- 主要做了2件事，实例化ActivityThread & 创建主线程Handler与Looper接收信息；
3.2 ActivityThread的attach函数：
private void attach(boolean system, long startSeq) {
//...
RuntimeInit.setApplicationObject(mAppThread.asBinder());
// 获取ActivityManagerService的代理对象
final IActivityManager mgr = ActivityManager.getService();// 1
try {
//通知AMS进行application的初始化
mgr.attachApplication(mAppThread, startSeq);// 2
} catch (RemoteException ex) {
throw ex.rethrowFromSystemServer();
}
}
- 注释1：获取ActivityManagerService的代理对象；
- 注释2：通过代理对象调用attachApplication()，获取启动application所需信息(应用进程相关数据)；
3.3 ActivityManagerService的attachApplication函数：
public final void attachApplication(IApplicationThread thread, long startSeq) {
synchronized (this) {
int callingPid = Binder.getCallingPid();
final int callingUid = Binder.getCallingUid();
final long origId = Binder.clearCallingIdentity();
attachApplicationLocked(thread, callingPid, callingUid, startSeq);// 1
Binder.restoreCallingIdentity(origId);
}
}
- 注释1：调用attachApplicationLocked()；
3.4 ActivityManagerService的attachApplicationLocked函数：
private final boolean attachApplicationLocked(IApplicationThread thread,
int pid, int callingUid, long startSeq) {
// 根据pid获取存储在AMS中，对应进程的相关信息
ProcessRecord app;
long startTime = SystemClock.uptimeMillis();
if (pid != MY_PID && pid >= 0) {
synchronized (mPidsSelfLocked) {
app = mPidsSelfLocked.get(pid);// 1
}
} else {
app = null;
}
// ...
thread.bindApplication(processName, appInfo, providers, null, profilerInfo, // 2
null, null, null, testMode,
mBinderTransactionTrackingEnabled, enableTrackAllocation,
isRestrictedBackupMode || !normalMode, app.persistent,
new Configuration(getGlobalConfiguration()), app.compat,
getCommonServicesLocked(app.isolated),
mCoreSettingsObserver.getCoreSettingsLocked(),
buildSerial, isAutofillCompatEnabled);
// ...
}
- 注释1：根据pid获取存储在AMS中，对应应用进程的相关信息；
- 注释2：通知ActivityThread启动application（IApplicationThread是ActivityThread的内部类，负责与ActivityManagerService通讯）；
3.5 ActivityThread的handleBindApplication函数：
- AMS中调用了ActivityThread的bindApplication函数，其内部其实是完成了Handler切换到主线程，并且最后活调用handleBindApplication(),下面我们看看其内部源码;
private void handleBindApplication(AppBindData data) {
// 将UI线程注册为运行时的虚拟机.
VMRuntime.registerSensitiveThread();
if (data.trackAllocation) {
DdmVmInternal.enableRecentAllocations(true);
}
// ...
// 创建上下文对象
final ContextImpl appContext = ContextImpl.createAppContext(this, data.info);
updateLocaleListFromAppContext(appContext,
mResourcesManager.getConfiguration().getLocales());
if (!Process.isIsolated()) {
final int oldMask = StrictMode.allowThreadDiskWritesMask();
try {
setupGraphicsSupport(appContext);
} finally {
StrictMode.setThreadPolicyMask(oldMask);
}
} else {
ThreadedRenderer.setIsolatedProcess(true);
}
// Continue loading instrumentation.
if (ii != null) {
// ...
} else {
mInstrumentation = new Instrumentation();// 1
mInstrumentation.basicInit(this);
}
Application app;
final StrictMode.ThreadPolicy savedPolicy = StrictMode.allowThreadDiskWrites();
final StrictMode.ThreadPolicy writesAllowedPolicy = StrictMode.getThreadPolicy();
try {
// If the app is being launched for full backup or restore, bring it up in
// a restricted environment with the base application class.
// 初始化Applcation类
app = data.info.makeApplication(data.restrictedBackupMode, null); // 2
// Propagate autofill compat state
app.setAutofillCompatibilityEnabled(data.autofillCompatibilityEnabled);
mInitialApplication = app;
// don't bring up providers in restricted mode; they may depend on the
// app's custom Application class
if (!data.restrictedBackupMode) {
if (!ArrayUtils.isEmpty(data.providers)) {
installContentProviders(app, data.providers);
// For process that contains content providers, we want to
// ensure that the JIT is enabled "at some point".
mH.sendEmptyMessageDelayed(H.ENABLE_JIT, 10*1000);
}
}
// Do this after providers, since instrumentation tests generally start their
// test thread at this point, and we don't want that racing.
try {
mInstrumentation.onCreate(data.instrumentationArgs); // 3
}
catch (Exception e) {
throw new RuntimeException(
"Exception thrown in onCreate() of "
+ data.instrumentationName + ": " + e.toString(), e);
}
try {
//调用Applcation的OnCreate函数
mInstrumentation.callApplicationOnCreate(app); // 4
} catch (Exception e) {
if (!mInstrumentation.onException(app, e)) {
throw new RuntimeException(
"Unable to create application " + app.getClass().getName()
+ ": " + e.toString(), e);
}
}
} finally {
// If the app targets < O-MR1, or doesn't change the thread policy
// during startup, clobber the policy to maintain behavior of b/36951662
if (data.appInfo.targetSdkVersion < Build.VERSION_CODES.O_MR1
|| StrictMode.getThreadPolicy().equals(writesAllowedPolicy)) {
StrictMode.setThreadPolicy(savedPolicy);
}
}
// Preload fonts resources
FontsContract.setApplicationContextForResources(appContext);
if (!Process.isIsolated()) {
try {
final ApplicationInfo info =
getPackageManager().getApplicationInfo(
data.appInfo.packageName,
PackageManager.GET_META_DATA /*flags*/,
UserHandle.myUserId());
if (info.metaData != null) {
final int preloadedFontsResource = info.metaData.getInt(
ApplicationInfo.METADATA_PRELOADED_FONTS, 0);
if (preloadedFontsResource != 0) {
data.info.getResources().preloadFonts(preloadedFontsResource);
}
}
} catch (RemoteException e) {
throw e.rethrowFromSystemServer();
}
}
}
- 注释1：创建Instrumentation，负责跟踪Application还在Activity的生命周期；
- 注释2：创建Application对象 & 调用其attach()；
- 注释3：调用Instrumentation的onCreate()，内部是空实现；
- 注释4：调用Instrumentation的callApplicationOnCreate()，内部是调用application的onCreate，如下代码；
public class Instrumentation {
public void callApplicationOnCreate(Application app) {
app.onCreate();
}
}
4.类关系
Application启动类结构.png
-
ActivityThread ：通过IActivityManager类，通知AMS准备application启动所需进程数据 ；
-
ActivityManagerService ：获取application启动所需进程数据 ；
-
Instrumentation ：创建&启动Application；跟踪Application的生命周期；
5.总结
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