1.前言
- 最近一直在看 《Android進階解密》 的一本書，這本書編寫邏輯、流程都非常好，而且很容易看懂，非常推薦大家去看看（沒有收廣告費，單純覺得作者寫的很好）。
- 上一篇簡單的介紹了Android進階（二）： 應用進程啟動過程，最終知道了ActivityThread就是代表應用進程。
- 今天就介紹ActivityThread啟動之后，是如何啟動
Application（基于Android 8.0 系統(tǒng)）。 - 文章中實例 linhaojian的Github
2.Application啟動過程的時序圖
Application啟動流程.png
3.源碼分析
3.1 ActivityThread初始化：
public static void main(String[] args) {
//...
//創(chuàng)建ActivityThread對象 & 調用attach()
ActivityThread thread = new ActivityThread();
thread.attach(false, startSeq);
//創(chuàng)建主線程的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);
//創(chuàng)建主線程的Looper
Looper.loop();
}
- 主要做了2件事，實例化ActivityThread & 創(chuàng)建主線程Handler與Looper接收信息；
3.2 ActivityThread的attach函數(shù)：
private void attach(boolean system, long startSeq) {
//...
RuntimeInit.setApplicationObject(mAppThread.asBinder());
// 獲取ActivityManagerService的代理對象
final IActivityManager mgr = ActivityManager.getService();// 1
try {
//通知AMS進行application的初始化
mgr.attachApplication(mAppThread, startSeq);// 2
} catch (RemoteException ex) {
throw ex.rethrowFromSystemServer();
}
}
- 注釋1：獲取ActivityManagerService的代理對象；
- 注釋2：通過代理對象調用attachApplication()，獲取啟動application所需信息(應用進程相關數(shù)據)；
3.3 ActivityManagerService的attachApplication函數(shù)：
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);
}
}
- 注釋1：調用attachApplicationLocked()；
3.4 ActivityManagerService的attachApplicationLocked函數(shù)：
private final boolean attachApplicationLocked(IApplicationThread thread,
int pid, int callingUid, long startSeq) {
// 根據pid獲取存儲在AMS中，對應進程的相關信息
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);
// ...
}
- 注釋1：根據pid獲取存儲在AMS中，對應應用進程的相關信息；
- 注釋2：通知ActivityThread啟動application（IApplicationThread是ActivityThread的內部類，負責與ActivityManagerService通訊）；
3.5 ActivityThread的handleBindApplication函數(shù)：
- AMS中調用了ActivityThread的bindApplication函數(shù)，其內部其實是完成了Handler切換到主線程，并且最后活調用handleBindApplication(),下面我們看看其內部源碼;
private void handleBindApplication(AppBindData data) {
// 將UI線程注冊為運行時的虛擬機.
VMRuntime.registerSensitiveThread();
if (data.trackAllocation) {
DdmVmInternal.enableRecentAllocations(true);
}
// ...
// 創(chuàng)建上下文對象
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類
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 {
//調用Applcation的OnCreate函數(shù)
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();
}
}
}
- 注釋1：創(chuàng)建Instrumentation，負責跟蹤Application還在Activity的生命周期；
- 注釋2：創(chuàng)建Application對象 & 調用其attach()；
- 注釋3：調用Instrumentation的onCreate()，內部是空實現(xiàn)；
- 注釋4：調用Instrumentation的callApplicationOnCreate()，內部是調用application的onCreate，如下代碼；
public class Instrumentation {
public void callApplicationOnCreate(Application app) {
app.onCreate();
}
}
4.類關系
Application啟動類結構.png
- ActivityThread ：通過IActivityManager類，通知AMS準備application啟動所需進程數(shù)據 ；
- ActivityManagerService ：獲取application啟動所需進程數(shù)據 ；
- Instrumentation ：創(chuàng)建&啟動Application；跟蹤Application的生命周期；
5.總結
- 到此，
Application啟動過程介紹完畢。 - 如果喜歡我的分享，可以點擊 關注 或者 贊，你們支持是我分享的最大動力 。
- linhaojian的Github
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