Android应用程序（activity）启动过程（二）
16lz
2021-01-23
继 Android应用程序（activity）启动过程（一），主要讲新进程和activity如何启动
yipianfengye_activity启动流程
- 从 第14步骤 调用 ActivityStack resumeTopActivityInnerLocked方法中最后面有一个方法startSpecificActivityLocked()。
if (!next.hasBeenLaunched) { next.hasBeenLaunched = true; } else { if (SHOW_APP_STARTING_PREVIEW) { next.showStartingWindow(null /* prev */, false /* newTask */, false /* taskSwich */); } if (DEBUG_SWITCH) Slog.v(TAG_SWITCH, "Restarting: " + next); } if (DEBUG_STATES) Slog.d(TAG_STATES, "resumeTopActivityLocked: Restarting " + next); // 开始启动新 activity mStackSupervisor.startSpecificActivityLocked(next, true, true);- 在startSpecificActivityLocked()判断当前Activity所需要的应用进程是否已经启动，若启动的话，则直接调用realStartAtivityLocked方法，否则调用startProcessLocked方法，用于启动应用进程
void startSpecificActivityLocked(ActivityRecord r, boolean andResume, boolean checkConfig) { // Is this activity's application already running? ProcessRecord app = mService.getProcessRecordLocked(r.processName, r.info.applicationInfo.uid, true); r.getStack().setLaunchTime(r); if (app != null && app.thread != null) { try { if ((r.info.flags&ActivityInfo.FLAG_MULTIPROCESS) == 0 || !"android".equals(r.info.packageName)) { app.addPackage(r.info.packageName, r.info.applicationInfo.versionCode, mService.mProcessStats); } // 进程已经启动 realStartActivityLocked(r, app, andResume, checkConfig); return; } catch (RemoteException e) { Slog.w(TAG, "Exception when starting activity " + r.intent.getComponent().flattenToShortString(), e); } // If a dead object exception was thrown -- fall through to // restart the application. } mService.startProcessLocked(r.processName, r.info.applicationInfo, true, 0, "activity", r.intent.getComponent(), false, false, true); }- 先查看进程未启动的情况 进入ActivityManagerService.startProcessLocked()
经过两次的方法重写，可以看到下面一段代码，在start()时传入了android.app.ActivityThread字符串，正式启动一个新进程
if (entryPoint == null) entryPoint = "android.app.ActivityThread"; Trace.traceBegin(Trace.TRACE_TAG_ACTIVITY_MANAGER, "Start proc: " + app.processName); checkTime(startTime, "startProcess: asking zygote to start proc"); Process.ProcessStartResult startResult = Process.start(entryPoint, app.processName, uid, uid, gids, debugFlags, mountExternal, app.info.targetSdkVersion, app.info.seinfo, requiredAbi, instructionSet, app.info.dataDir, entryPointArgs);- 在Process.start()中 代码很简单，直接进入到startViaZygote() 翻译：开始孵化？
try { return startViaZygote(processClass, niceName, uid, gid, gids, debugFlags, mountExternal, targetSdkVersion, seInfo, abi, instructionSet, appDataDir, zygoteArgs); } catch (ZygoteStartFailedEx ex) { Log.e(LOG_TAG, "Starting VM process through Zygote failed"); throw new RuntimeException( "Starting VM process through Zygote failed", ex); }- 在startViaZygote()方法中又直接调用了zygoteSendArgsAndGetResult();
private static ProcessStartResult zygoteSendArgsAndGetResult( ZygoteState zygoteState, ArrayList args) throws ZygoteStartFailedEx { try { // Throw early if any of the arguments are malformed. This means we can // avoid writing a partial response to the zygote. int sz = args.size(); for (int i = 0; i < sz; i++) { if (args.get(i).indexOf('\n') >= 0) { throw new ZygoteStartFailedEx("embedded newlines not allowed"); } } final BufferedWriter writer = zygoteState.writer; final DataInputStream inputStream = zygoteState.inputStream; writer.write(Integer.toString(args.size())); writer.newLine(); for (int i = 0; i < sz; i++) { String arg = args.get(i); writer.write(arg); writer.newLine(); } writer.flush(); // Should there be a timeout on this? ProcessStartResult result = new ProcessStartResult(); // Always read the entire result from the input stream to avoid leaving // bytes in the stream for future process starts to accidentally stumble // upon. result.pid = inputStream.readInt(); result.usingWrapper = inputStream.readBoolean(); if (result.pid < 0) { throw new ZygoteStartFailedEx("fork() failed"); } return result; } catch (IOException ex) { zygoteState.close(); throw new ZygoteStartFailedEx(ex); } } 可以发现其最终调用了Zygote并通过socket通信的方式让Zygote进程fork除了一个新的进程，并根据我们刚刚传递的"android.app.ActivityThread"字符串，反射出该对象并执行ActivityThread的main方法。这样我们所要启动的应用进程这时候其实已经启动了，但是还没有执行相应的初始化操作。
43. 通过 openZygoteSocketIfNeeded(）---->ZygoteState.connect()---->zygoteSocket.connect()---->impl.connect(),调用Native方法connectLocal()。具体进程怎么启动的这又是一个话题。。。
44. 当进程启动完成后就进入ActivityThread类的main方法
public static void main(String[] args) { Trace.traceBegin(Trace.TRACE_TAG_ACTIVITY_MANAGER, "ActivityThreadMain");... ... EventLogger.setReporter(new EventLoggingReporter()); ... ... Process.setArgV0(""); Looper.prepareMainLooper(); ActivityThread thread = new ActivityThread(); thread.attach(false); if (sMainThreadHandler == null) { sMainThreadHandler = thread.getHandler(); } if (false) { Looper.myLooper().setMessageLogging(new LogPrinter(Log.DEBUG, "ActivityThread")); } ... ... Looper.loop(); throw new RuntimeException("Main thread loop unexpectedly exited"); } - 在main方法中调用了Looper.prepareMainLooper(); Looper.loop();方法，这就是为什么在activity（主线程）直接new handler，使用handler不报错的原因，在子线程要先调用prepare方法。下面是主要方法 thread.attach(false);
final IActivityManager mgr = ActivityManagerNative.getDefault(); try { mgr.attachApplication(mAppThread); } catch (RemoteException ex) { throw ex.rethrowFromSystemServer(); }- 通过ActivityManagerNative中ActivityManagerProxy的attachApplication方法发送到服务端，ActivityManagerNative的实现类ActivityManagerService中attachApplication()
@Override public final void attachApplication(IApplicationThread thread) { synchronized (this) { int callingPid = Binder.getCallingPid(); final long origId = Binder.clearCallingIdentity(); attachApplicationLocked(thread, callingPid); Binder.restoreCallingIdentity(origId); } }- 代码很简洁，直接进入attachApplicationLocked
// See if the top visible activity is waiting to run in this process... if (normalMode) { try { if (mStackSupervisor.attachApplicationLocked(app)) { didSomething = true; } } catch (Exception e) { Slog.wtf(TAG, "Exception thrown launching activities in " + app, e); badApp = true; } }- 摸索到了这一段代码 mStackSupervisor.attachApplicationLocked(app)
boolean attachApplicationLocked(ProcessRecord app) throws RemoteException { final String processName = app.processName; boolean didSomething = false; for (int displayNdx = mActivityDisplays.size() - 1; displayNdx >= 0; --displayNdx) { ArrayList stacks = mActivityDisplays.valueAt(displayNdx).mStacks; for (int stackNdx = stacks.size() - 1; stackNdx >= 0; --stackNdx) { final ActivityStack stack = stacks.get(stackNdx); if (!isFocusedStack(stack)) { continue; } ActivityRecord hr = stack.topRunningActivityLocked(); if (hr != null) { if (hr.app == null && app.uid == hr.info.applicationInfo.uid && processName.equals(hr.processName)) { try { if (realStartActivityLocked(hr, app, true, true)) { didSomething = true; } } catch (RemoteException e) { Slog.w(TAG, "Exception in new application when starting activity " + hr.intent.getComponent().flattenToShortString(), e); throw e; } } } } } if (!didSomething) { ensureActivitiesVisibleLocked(null, 0, !PRESERVE_WINDOWS); } return didSomething; }- 我又重新看到了realStartActivityLocked()，又找到了组织，重新回到 step.39。这时候就是开始启动activity了
app.thread.scheduleLaunchActivity(new Intent(r.intent), r.appToken, System.identityHashCode(r), r.info, new Configuration(mService.mConfiguration), new Configuration(task.mOverrideConfig), r.compat, r.launchedFromPackage, task.voiceInteractor, app.repProcState, r.icicle, r.persistentState, results, newIntents, !andResume, mService.isNextTransitionForward(), profilerInfo);- 通过IApplicationThread调用了scheduleLaunchActivity，最终实现是在ActivityThread内部类ApplicationThread实现的，然后通过Handler调用handleLaunchActivity()
case LAUNCH_ACTIVITY: { Trace.traceBegin(Trace.TRACE_TAG_ACTIVITY_MANAGER, "activityStart"); final ActivityClientRecord r = (ActivityClientRecord) msg.obj; r.packageInfo = getPackageInfoNoCheck( r.activityInfo.applicationInfo, r.compatInfo); handleLaunchActivity(r, null, "LAUNCH_ACTIVITY"); Trace.traceEnd(Trace.TRACE_TAG_ACTIVITY_MANAGER); } break;- ActivityThread类 handleLaunchActivity 中有performLaunchActivity，handleResumeActivity，performPauseActivityIfNeeded
private void handleLaunchActivity(ActivityClientRecord r, Intent customIntent, String reason) {... ... Activity a = performLaunchActivity(r, customIntent); if (a != null) { r.createdConfig = new Configuration(mConfiguration); reportSizeConfigurations(r); Bundle oldState = r.state; ... ... handleResumeActivity(r.token, false, r.isForward, !r.activity.mFinished && !r.startsNotResumed, r.lastProcessedSeq, reason); if (!r.activity.mFinished && r.startsNotResumed) { ... ... performPauseActivityIfNeeded(r, reason); .. .. if (r.isPreHoneycomb()) { r.state = oldState; } } } else { try { ActivityManagerNative.getDefault() .finishActivity(r.token, Activity.RESULT_CANCELED, null, Activity.DONT_FINISH_TASK_WITH_ACTIVITY); } catch (RemoteException ex) { throw ex.rethrowFromSystemServer(); } } }- performLaunchActivity中主要代码，newActivity(),通过类加载机制创建activity
try { java.lang.ClassLoader cl = r.packageInfo.getClassLoader(); activity = mInstrumentation.newActivity( cl, component.getClassName(), r.intent); StrictMode.incrementExpectedActivityCount(activity.getClass()); r.intent.setExtrasClassLoader(cl); r.intent.prepareToEnterProcess(); if (r.state != null) { r.state.setClassLoader(cl); } } // 创建Activity通过类加载机制 public Activity newActivity(ClassLoader cl, String className, Intent intent) throws InstantiationException, IllegalAccessException, ClassNotFoundException { return (Activity)cl.loadClass(className).newInstance(); }- 还是当前方法，开始activity onCreate方法
activity.mCalled = false; if (r.isPersistable()) { mInstrumentation.callActivityOnCreate(activity, r.state, r.persistentState); } else { mInstrumentation.callActivityOnCreate(activity, r.state); }- 直接进入Instrumentation，
public void callActivityOnCreate(Activity activity, Bundle icicle) { prePerformCreate(activity); activity.performCreate(icicle); postPerformCreate(activity); }// Activity final void performCreate(Bundle icicle) { restoreHasCurrentPermissionRequest(icicle); onCreate(icicle); mActivityTransitionState.readState(icicle); performCreateCommon(); }- 紧接着下面四五行代码，进入onstart()
if (!r.activity.mFinished) { activity.performStart(); r.stopped = false; }- 恢复activity 被回收时保存的数据
if (!r.activity.mFinished) { if (r.isPersistable()) { if (r.state != null || r.persistentState != null) { mInstrumentation.callActivityOnRestoreInstanceState(activity, r.state, r.persistentState); } } else if (r.state != null) { mInstrumentation.callActivityOnRestoreInstanceState(activity, r.state); } } if (!r.activity.mFinished) { activity.mCalled = false; if (r.isPersistable()) { // 活动启动完成时调用(在{@link #onStart}和{@link #onRestoreInstanceState}调用之后)。 应用程序通常不会实现这种方法;它用于系统类在应用程序代码运行之后进行最终初始化。， mInstrumentation.callActivityOnPostCreate(activity, r.state, r.persistentState); } else { mInstrumentation.callActivityOnPostCreate(activity, r.state); } if (!activity.mCalled) { throw new SuperNotCalledException( "Activity " + r.intent.getComponent().toShortString() + " did not call through to super.onPostCreate()"); } }- 返回step 52 进入 handleResumeActivity，流程基本一样我就不往下分析了，现在及完成了activity onDestory到onCreate所有生命周期，祝大家收货满满！
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