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Android进阶宝典 — 史上最详细Android系统启动全流程分析
在本篇文章开始之前，我们先看一张老图，相信伙伴们非常熟悉：
这是从Launcher点击App到App首页展示的一个流程图，如果之前总是记不住这张图中形形色色流程，相信看过前两篇文章之后，就非常熟悉其中的流程了，那么我根据上一篇文章中，关于App进程的启动整理出一张关系图：
当Application执行onCreate方法之后，App进程算是已经启动了，这个时候，我们看下Activity是如何启动的？
1 Activity的启动流程分析
当我们启动一个Activity的时候，通常都是采用显示意图，创建一个Intent对象，调用startActivity方法启动，那么其内部是如何完成Activity的启动的呢？
fun open(context: Context, url: String) {
val intent = Intent()
intent.setClass(context, WebActivity::class.java)
intent.putExtra("url", url)
context.startActivity(intent)
}
1.1 Intent意图解析
既然我们要启动一个Activity，那么首先需要知道我们要跳转到哪里？这些包括目的地，以及参数都是封装在了Intent中，首先我们跟进startActivity源码，看下Intent意图是如何被解析的。
try {
intent.migrateExtraStreamToClipData(who);
intent.prepareToLeaveProcess(who);
int result = ActivityTaskManager.getService().startActivity(whoThread,
who.getOpPackageName(), who.getAttributionTag(), intent,
intent.resolveTypeIfNeeded(who.getContentResolver()), token,
target != null ? target.mEmbeddedID : null, requestCode, 0, null, options);
checkStartActivityResult(result, intent);
} catch (RemoteException e) {
throw new RuntimeException("Failure from system", e);
}
当我们在上层调用startActivity启动的时候，其实最终还是调用了ATSM的startActivity方法，从源码中便能看出端倪，所以Activity的启动，最终还是得先进入到system_server进程当中。
ActivityManagerService # startActivity
public int startActivity(IApplicationThread caller, String callingPackage,
Intent intent, String resolvedType, IBinder resultTo, String resultWho, int requestCode,
int startFlags, ProfilerInfo profilerInfo, Bundle bOptions) {
return mActivityTaskManager.startActivity(caller, callingPackage, null, intent,
resolvedType, resultTo, resultWho, requestCode, startFlags, profilerInfo, bOptions);
}
我们看到，在AMS中的startActivity方法，最终是调用到了ATMS的startActivity，所以进入ATMS。
ATMS # startActivity
@Override
public final int startActivity(IApplicationThread caller, String callingPackage,
String callingFeatureId, Intent intent, String resolvedType, IBinder resultTo,
String resultWho, int requestCode, int startFlags, ProfilerInfo profilerInfo,
Bundle bOptions) {
return startActivityAsUser(caller, callingPackage, callingFeatureId, intent, resolvedType,
resultTo, resultWho, requestCode, startFlags, profilerInfo, bOptions,
UserHandle.getCallingUserId());
}
ATMS # startActivityAsUser
private int startActivityAsUser(IApplicationThread caller, String callingPackage,
@Nullable String callingFeatureId, Intent intent, String resolvedType,
IBinder resultTo, String resultWho, int requestCode, int startFlags,
ProfilerInfo profilerInfo, Bundle bOptions, int userId, boolean validateIncomingUser) {
assertPackageMatchesCallingUid(callingPackage);
enforceNotIsolatedCaller("startActivityAsUser");
userId = getActivityStartController().checkTargetUser(userId, validateIncomingUser,
Binder.getCallingPid(), Binder.getCallingUid(), "startActivityAsUser");
// TODO: Switch to user app stacks here.
return getActivityStartController().obtainStarter(intent, "startActivityAsUser")
.setCaller(caller)
.setCallingPackage(callingPackage)
.setCallingFeatureId(callingFeatureId)
.setResolvedType(resolvedType)
.setResultTo(resultTo)
.setResultWho(resultWho)
.setRequestCode(requestCode)
.setStartFlags(startFlags)
.setProfilerInfo(profilerInfo)
.setActivityOptions(bOptions)
.setUserId(userId)
.execute();
}
我们看到，最终调用startActivityAsUser，首先获取一个ActivityStartController，那么这个是干什么的呢？
ActivityStartController getActivityStartController() {
return mActivityStartController;
}
ActivityStartController，顾名思义是Activity启动的一个管理类，主要是用来管理Activity启动中需要用到的Intent信息和flag标识，它的初始化是在ATMS初始化时创建的。
ActivityStartController(ActivityTaskManagerService service) {
this(service, service.mTaskSupervisor,
new DefaultFactory(service, service.mTaskSupervisor,
new ActivityStartInterceptor(service, service.mTaskSupervisor)));
}
ActivityStarter obtainStarter(Intent intent, String reason) {
return mFactory.obtain().setIntent(intent).setReason(reason);
}
而且通过ActivityStartController可以获取一个ActivityStarter对象，获取对象时是通过mFactory获取，而mFactory是在ActivityStartController初始化时创建的，为DefaultFactory。
static class DefaultFactory implements Factory {
/**
* The maximum count of starters that should be active at one time:
* 1. last ran starter (for logging and post activity processing)
* 2. current running starter
* 3. starter from re-entry in (2)
*/
private final int MAX_STARTER_COUNT = 3;
private ActivityStartController mController;
private ActivityTaskManagerService mService;
private ActivityTaskSupervisor mSupervisor;
private ActivityStartInterceptor mInterceptor;
private SynchronizedPool<ActivityStarter> mStarterPool =
new SynchronizedPool<>(MAX_STARTER_COUNT);
DefaultFactory(ActivityTaskManagerService service,
ActivityTaskSupervisor supervisor, ActivityStartInterceptor interceptor) {
mService = service;
mSupervisor = supervisor;
mInterceptor = interceptor;
}
@Override
public void setController(ActivityStartController controller) {
mController = controller;
}
@Override
public ActivityStarter obtain() {
ActivityStarter starter = mStarterPool.acquire();
if (starter == null) {
if (mService.mRootWindowContainer == null) {
throw new IllegalStateException("Too early to start activity.");
}
starter = new ActivityStarter(mController, mService, mSupervisor, mInterceptor);
}
return starter;
}
@Override
public void recycle(ActivityStarter starter) {
starter.reset(true /* clearRequest*/);
mStarterPool.release(starter);
}
}
ActivityStarter对象就是用来解析Intent意图中的信息。在startActivityAsUser方法中，我们看到在拿到ActivityStarter之后，采用的建造者设计模式给某个对象赋值，包括像setIntent，都是给Request对象赋值；
ActivityStarter setIntent(Intent intent) {
mRequest.intent = intent;
return this;
}
最终调用了execute方法，这个方法是ActivityStarter的核心方法，也是在启动Activity之前做的准备工作。
ActivityStarter # execute
所以前面的过程相当于一直在构建Request对象，最后一步执行请求。
/**
* Resolve necessary information according the request parameters provided earlier, and execute
* the request which begin the journey of starting an activity.
* @return The starter result.
*/
int execute() {
try {
// Refuse possible leaked file descriptors
if (mRequest.intent != null && mRequest.intent.hasFileDescriptors()) {
throw new IllegalArgumentException("File descriptors passed in Intent");
}
final LaunchingState launchingState;
synchronized (mService.mGlobalLock) {
final ActivityRecord caller = ActivityRecord.forTokenLocked(mRequest.resultTo);
final int callingUid = mRequest.realCallingUid == Request.DEFAULT_REAL_CALLING_UID
? Binder.getCallingUid() : mRequest.realCallingUid;
launchingState = mSupervisor.getActivityMetricsLogger().notifyActivityLaunching(
mRequest.intent, caller, callingUid);
}
// If the caller hasn't already resolved the activity, we're willing
// to do so here. If the caller is already holding the WM lock here,
// and we need to check dynamic Uri permissions, then we're forced
// to assume those permissions are denied to avoid deadlocking.
if (mRequest.activityInfo == null) {
mRequest.resolveActivity(mSupervisor);
}
// Add checkpoint for this shutdown or reboot attempt, so we can record the original
// intent action and package name.
if (mRequest.intent != null) {
String intentAction = mRequest.intent.getAction();
String callingPackage = mRequest.callingPackage;
if (intentAction != null && callingPackage != null
&& (Intent.ACTION_REQUEST_SHUTDOWN.equals(intentAction)
|| Intent.ACTION_SHUTDOWN.equals(intentAction)
|| Intent.ACTION_REBOOT.equals(intentAction))) {
ShutdownCheckPoints.recordCheckPoint(intentAction, callingPackage, null);
}
}
int res;
synchronized (mService.mGlobalLock) {
final boolean globalConfigWillChange = mRequest.globalConfig != null
&& mService.getGlobalConfiguration().diff(mRequest.globalConfig) != 0;
final Task rootTask = mRootWindowContainer.getTopDisplayFocusedRootTask();
if (rootTask != null) {
rootTask.mConfigWillChange = globalConfigWillChange;
}
ProtoLog.v(WM_DEBUG_CONFIGURATION, "Starting activity when config "
+ "will change = %b", globalConfigWillChange);
final long origId = Binder.clearCallingIdentity();
res = resolveToHeavyWeightSwitcherIfNeeded();
if (res != START_SUCCESS) {
return res;
}
//核心代码 1
res = executeRequest(mRequest);
Binder.restoreCallingIdentity(origId);
if (globalConfigWillChange) {
// If the caller also wants to switch to a new configuration, do so now.
// This allows a clean switch, as we are waiting for the current activity
// to pause (so we will not destroy it), and have not yet started the
// next activity.
mService.mAmInternal.enforceCallingPermission(
android.Manifest.permission.CHANGE_CONFIGURATION,
"updateConfiguration()");
if (rootTask != null) {
rootTask.mConfigWillChange = false;
}
ProtoLog.v(WM_DEBUG_CONFIGURATION,
"Updating to new configuration after starting activity.");
mService.updateConfigurationLocked(mRequest.globalConfig, null, false);
}
// The original options may have additional info about metrics. The mOptions is not
// used here because it may be cleared in setTargetRootTaskIfNeeded.
final ActivityOptions originalOptions = mRequest.activityOptions != null
? mRequest.activityOptions.getOriginalOptions() : null;
// If the new record is the one that started, a new activity has created.
final boolean newActivityCreated = mStartActivity == mLastStartActivityRecord;
// Notify ActivityMetricsLogger that the activity has launched.
// ActivityMetricsLogger will then wait for the windows to be drawn and populate
// WaitResult.
mSupervisor.getActivityMetricsLogger().notifyActivityLaunched(launchingState, res,
newActivityCreated, mLastStartActivityRecord, originalOptions);
if (mRequest.waitResult != null) {
mRequest.waitResult.result = res;
res = waitResultIfNeeded(mRequest.waitResult, mLastStartActivityRecord,
launchingState);
}
return getExternalResult(res);
}
} finally {
onExecutionComplete();
}
}
其实前面都是在做一系列的判断，最终是调用了executeRequest方法，把Request传进去了。
private int executeRequest(Request request) {
// ...... 前面一系列的判断，权限检测等，不是关注的重点
final ActivityRecord r = new ActivityRecord.Builder(mService)
.setCaller(callerApp)
.setLaunchedFromPid(callingPid)
.setLaunchedFromUid(callingUid)
.setLaunchedFromPackage(callingPackage)
.setLaunchedFromFeature(callingFeatureId)
.setIntent(intent)
.setResolvedType(resolvedType)
.setActivityInfo(aInfo)
.setConfiguration(mService.getGlobalConfiguration())
.setResultTo(resultRecord)
.setResultWho(resultWho)
.setRequestCode(requestCode)
.setComponentSpecified(request.componentSpecified)
.setRootVoiceInteraction(voiceSession != null)
.setActivityOptions(checkedOptions)
.setSourceRecord(sourceRecord)
.build();
mLastStartActivityRecord = r;
if (r.appTimeTracker == null && sourceRecord != null) {
// If the caller didn't specify an explicit time tracker, we want to continue
// tracking under any it has.
r.appTimeTracker = sourceRecord.appTimeTracker;
}
// Only allow app switching to be resumed if activity is not a restricted background
// activity and target app is not home process, otherwise any background activity
// started in background task can stop home button protection mode.
// As the targeted app is not a home process and we don't need to wait for the 2nd
// activity to be started to resume app switching, we can just enable app switching
// directly.
WindowProcessController homeProcess = mService.mHomeProcess;
boolean isHomeProcess = homeProcess != null
&& aInfo.applicationInfo.uid == homeProcess.mUid;
if (!restrictedBgActivity && !isHomeProcess) {
mService.resumeAppSwitches();
}
mLastStartActivityResult = startActivityUnchecked(r, sourceRecord, voiceSession,
request.voiceInteractor, startFlags, true /* doResume */, checkedOptions,
inTask, inTaskFragment, restrictedBgActivity, intentGrants);
if (request.outActivity != null) {
request.outActivity[0] = mLastStartActivityRecord;
}
return mLastStartActivityResult;
}
通常在启动Activity的时候，是从ActivityA跳转到ActivityB，所以Activity在ATMS中都是以ActivityRecord的形式存在的，所以当执行Request的请求的时候，也是创建了要启动的Activity的ActivityRecord对象，调用startActivityUnchecked方法。
因为在调用startActivityUnchecked，大部分的检查都已经完成了，而且调用方也有足够的权限启动Activity，所以这个方法就是真正去启动Activity了。
ActivityStarter # startActivityUnchecked
private int startActivityUnchecked(final ActivityRecord r, ActivityRecord sourceRecord,
IVoiceInteractionSession voiceSession, IVoiceInteractor voiceInteractor,
int startFlags, boolean doResume, ActivityOptions options, Task inTask,
TaskFragment inTaskFragment, boolean restrictedBgActivity,
NeededUriGrants intentGrants) {
int result = START_CANCELED;
boolean startResultSuccessful = false;
final Task startedActivityRootTask;
// ......
try {
//
result = startActivityInner(r, sourceRecord, voiceSession, voiceInteractor,
startFlags, doResume, options, inTask, inTaskFragment, restrictedBgActivity,
intentGrants);
startResultSuccessful = ActivityManager.isStartResultSuccessful(result);
final boolean taskAlwaysOnTop = options != null && options.getTaskAlwaysOnTop();
// Apply setAlwaysOnTop when starting an Activity is successful regardless of creating
// a new Activity or recycling the existing Activity.
if (taskAlwaysOnTop && startResultSuccessful) {
final Task targetRootTask =
mTargetRootTask != null ? mTargetRootTask : mTargetTask.getRootTask();
targetRootTask.setAlwaysOnTop(true);
}
}
postStartActivityProcessing(r, result, startedActivityRootTask);
return result;
}
ActivityStarter # startActivityInner
/**
* @params r 要启动的Activity
* @params sourceRecord 当前Activity
*/
int startActivityInner(final ActivityRecord r, ActivityRecord sourceRecord,
IVoiceInteractionSession voiceSession, IVoiceInteractor voiceInteractor,
int startFlags, boolean doResume, ActivityOptions options, Task inTask,
TaskFragment inTaskFragment, boolean restrictedBgActivity,
NeededUriGrants intentGrants) {
setInitialState(r, options, inTask, inTaskFragment, doResume, startFlags, sourceRecord,
voiceSession, voiceInteractor, restrictedBgActivity);
//计算启动模式
computeLaunchingTaskFlags();
//计算源Activity所在的任务栈
computeSourceRootTask();
//设置Launche Flag
mIntent.setFlags(mLaunchFlags);
// ......
//启动黑白屏
mTargetRootTask.startActivityLocked(mStartActivity,
topRootTask != null ? topRootTask.getTopNonFinishingActivity() : null, newTask,
isTaskSwitch, mOptions, sourceRecord);
if (mDoResume) {
final ActivityRecord topTaskActivity = startedTask.topRunningActivityLocked();
if (!mTargetRootTask.isTopActivityFocusable()
|| (topTaskActivity != null && topTaskActivity.isTaskOverlay()
&& mStartActivity != topTaskActivity)) {
// If the activity is not focusable, we can't resume it, but still would like to
// make sure it becomes visible as it starts (this will also trigger entry
// animation). An example of this are PIP activities.
// Also, we don't want to resume activities in a task that currently has an overlay
// as the starting activity just needs to be in the visible paused state until the
// over is removed.
// Passing {@code null} as the start parameter ensures all activities are made
// visible.
mTargetRootTask.ensureActivitiesVisible(null /* starting */,
0 /* configChanges */, !PRESERVE_WINDOWS);
// Go ahead and tell window manager to execute app transition for this activity
// since the app transition will not be triggered through the resume channel.
mTargetRootTask.mDisplayContent.executeAppTransition();
} else {
// If the target root-task was not previously focusable (previous top running
// activity on that root-task was not visible) then any prior calls to move the
// root-task to the will not update the focused root-task. If starting the new
// activity now allows the task root-task to be focusable, then ensure that we
// now update the focused root-task accordingly.
if (mTargetRootTask.isTopActivityFocusable()
&& !mRootWindowContainer.isTopDisplayFocusedRootTask(mTargetRootTask)) {
mTargetRootTask.moveToFront("startActivityInner");
}
mRootWindowContainer.resumeFocusedTasksTopActivities(
mTargetRootTask, mStartActivity, mOptions, mTransientLaunch);
}
}
mRootWindowContainer.updateUserRootTask(mStartActivity.mUserId, mTargetRootTask);
// Update the recent tasks list immediately when the activity starts
mSupervisor.mRecentTasks.add(startedTask);
mSupervisor.handleNonResizableTaskIfNeeded(startedTask,
mPreferredWindowingMode, mPreferredTaskDisplayArea, mTargetRootTask);
return START_SUCCESS;
}
我们看这个方法中有两个参数分别为：r和sourceRecord，其中r代表要启动的ActivityRecord，sourceRecord代表源Activity，所以在startActivityInner方法中，首先
- 判断当前要启动的Activity的启动模式；
- 有了要启动Activity的启动模式，那么就需要获取源Activity的任务栈，判断要启动的Activity要放在哪个任务栈，还是需要另起一个任务栈。
- 当我们点击Launcher icon时，这个时候其实也是启动Activity的过程，但是这个时候进程还未创建完成，那么就会展示一个黑白屏占位，等到Activity真正启动之后，再显示。
1.2 Activity栈管理
当计算完成任务栈的各种信息之后，就会调用RootWindowContainer的resumeFocusedTasksTopActivities方法。RootWindowContainer是一个窗口管理器，用于管理全部的窗口展示，对于窗口是否可见也是由RootWindowContainer来控制的。
RootWindowContainer # resumeFocusedTasksTopActivities
boolean resumeFocusedTasksTopActivities(
Task targetRootTask, ActivityRecord target, ActivityOptions targetOptions,
boolean deferPause) {
if (!mTaskSupervisor.readyToResume()) {
return false;
}
boolean result = false;
if (targetRootTask != null && (targetRootTask.isTopRootTaskInDisplayArea()
|| getTopDisplayFocusedRootTask() == targetRootTask)) {
result = targetRootTask.resumeTopActivityUncheckedLocked(target, targetOptions,
deferPause);
}
for (int displayNdx = getChildCount() - 1; displayNdx >= 0; --displayNdx) {
final DisplayContent display = getChildAt(displayNdx);
final boolean curResult = result;
boolean[] resumedOnDisplay = new boolean[1];
display.forAllRootTasks(rootTask -> {
final ActivityRecord topRunningActivity = rootTask.topRunningActivity();
if (!rootTask.isFocusableAndVisible() || topRunningActivity == null) {
return;
}
if (rootTask == targetRootTask) {
// Simply update the result for targetRootTask because the targetRootTask
// had already resumed in above. We don't want to resume it again,
// especially in some cases, it would cause a second launch failure
// if app process was dead.
resumedOnDisplay[0] |= curResult;
return;
}
if (rootTask.getDisplayArea().isTopRootTask(rootTask)
&& topRunningActivity.isState(RESUMED)) {
// Kick off any lingering app transitions form the MoveTaskToFront
// operation, but only consider the top task and root-task on that
// display.
rootTask.executeAppTransition(targetOptions);
} else {
resumedOnDisplay[0] |= topRunningActivity.makeActiveIfNeeded(target);
}
});
result |= resumedOnDisplay[0];
if (!resumedOnDisplay[0]) {
// In cases when there are no valid activities (e.g. device just booted or launcher
// crashed) it's possible that nothing was resumed on a display. Requesting resume
// of top activity in focused root task explicitly will make sure that at least home
// activity is started and resumed, and no recursion occurs.
final Task focusedRoot = display.getFocusedRootTask();
if (focusedRoot != null) {
result |= focusedRoot.resumeTopActivityUncheckedLocked(target, targetOptions);
} else if (targetRootTask == null) {
result |= resumeHomeActivity(null /* prev */, "no-focusable-task",
display.getDefaultTaskDisplayArea());
}
}
}
return result;
}
因为对于Activity来说是存在任务栈的这个概念的，通常存储在FocusedTasks，当前台的Activity展示的时候是放在栈顶的，所以是否需要显示这个Activity，也是由RootWindowContainer来决定的。
接下来就到了Activity任务栈的处理，调用了Task的resumeTopActivityUncheckedLocked方法，最终
调用了resumeTopActivityInnerLocked方法。
Task # resumeTopActivityInnerLocked
private boolean resumeTopActivityInnerLocked(ActivityRecord prev, ActivityOptions options,
boolean deferPause) {
if (!mAtmService.isBooting() && !mAtmService.isBooted()) {
// Not ready yet!
return false;
}
final ActivityRecord topActivity = topRunningActivity(true /* focusableOnly */);
if (topActivity == null) {
// There are no activities left in this task, let's look somewhere else.
return resumeNextFocusableActivityWhenRootTaskIsEmpty(prev, options);
}
final boolean[] resumed = new boolean[1];
final TaskFragment topFragment = topActivity.getTaskFragment();
resumed[0] = topFragment.resumeTopActivity(prev, options, deferPause);
forAllLeafTaskFragments(f -> {
if (topFragment == f) {
return;
}
if (!f.canBeResumed(null /* starting */)) {
return;
}
resumed[0] |= f.resumeTopActivity(prev, options, deferPause);
}, true);
return resumed[0];
}
其实这个方法从名字上看，应该就是将栈顶的Activity置为可见可交互的状态，所以这里执行了TaskFragment的resumeTopActivity，我们看下具体的实现逻辑。
TaskFragment # resumeTopActivity
final boolean resumeTopActivity(ActivityRecord prev, ActivityOptions options,
boolean deferPause) {
//要启动的Activity
ActivityRecord next = topRunningActivity(true /* focusableOnly */);
// ......
boolean pausing = !deferPause && taskDisplayArea.pauseBackTasks(next);
if (mResumedActivity != null) {
ProtoLog.d(WM_DEBUG_STATES, "resumeTopActivity: Pausing %s", mResumedActivity);
//将当前展示Activity置为Pause
pausing |= startPausing(mTaskSupervisor.mUserLeaving, false /* uiSleeping */,
next, "resumeTopActivity");
}
// .......
// 判断要启动的ACtivity进程是否存在
if (next.attachedToProcess()) {
if (DEBUG_SWITCH) {
Slog.v(TAG_SWITCH, "Resume running: " + next + " stopped=" + next.stopped
+ " visibleRequested=" + next.mVisibleRequested);
}
// If the previous activity is translucent, force a visibility update of
// the next activity, so that it's added to WM's opening app list, and
// transition animation can be set up properly.
// For example, pressing Home button with a translucent activity in focus.
// Launcher is already visible in this case. If we don't add it to opening
// apps, maybeUpdateTransitToWallpaper() will fail to identify this as a
// TRANSIT_WALLPAPER_OPEN animation, and run some funny animation.
final boolean lastActivityTranslucent = inMultiWindowMode()
|| mLastPausedActivity != null && !mLastPausedActivity.occludesParent();
// This activity is now becoming visible.
if (!next.mVisibleRequested || next.stopped || lastActivityTranslucent) {
next.setVisibility(true);
}
// schedule launch ticks to collect information about slow apps.
next.startLaunchTickingLocked();
ActivityRecord lastResumedActivity =
lastFocusedRootTask == null ? null
: lastFocusedRootTask.getTopResumedActivity();
final ActivityRecord.State lastState = next.getState();
mAtmService.updateCpuStats();
ProtoLog.v(WM_DEBUG_STATES, "Moving to RESUMED: %s (in existing)", next);
next.setState(RESUMED, "resumeTopActivity");
// Have the window manager re-evaluate the orientation of
// the screen based on the new activity order.
boolean notUpdated = true;
// Activity should also be visible if set mLaunchTaskBehind to true (see
// ActivityRecord#shouldBeVisibleIgnoringKeyguard()).
if (shouldBeVisible(next)) {
// We have special rotation behavior when here is some active activity that
// requests specific orientation or Keyguard is locked. Make sure all activity
// visibilities are set correctly as well as the transition is updated if needed
// to get the correct rotation behavior. Otherwise the following call to update
// the orientation may cause incorrect configurations delivered to client as a
// result of invisible window resize.
// TODO: Remove this once visibilities are set correctly immediately when
// starting an activity.
notUpdated = !mRootWindowContainer.ensureVisibilityAndConfig(next, getDisplayId(),
true /* markFrozenIfConfigChanged */, false /* deferResume */);
}
if (notUpdated) {
// The configuration update wasn't able to keep the existing
// instance of the activity, and instead started a new one.
// We should be all done, but let's just make sure our activity
// is still at the top and schedule another run if something
// weird happened.
ActivityRecord nextNext = topRunningActivity();
ProtoLog.i(WM_DEBUG_STATES, "Activity config changed during resume: "
+ "%s, new next: %s", next, nextNext);
if (nextNext != next) {
// Do over!
mTaskSupervisor.scheduleResumeTopActivities();
}
if (!next.mVisibleRequested || next.stopped) {
next.setVisibility(true);
}
next.completeResumeLocked();
return true;
}
try {
final ClientTransaction transaction =
ClientTransaction.obtain(next.app.getThread(), next.appToken);
// Deliver all pending results.
ArrayList<ResultInfo> a = next.results;
if (a != null) {
final int size = a.size();
if (!next.finishing && size > 0) {
if (DEBUG_RESULTS) {
Slog.v(TAG_RESULTS, "Delivering results to " + next + ": " + a);
}
transaction.addCallback(ActivityResultItem.obtain(a));
}
}
if (next.newIntents != null) {
transaction.addCallback(
NewIntentItem.obtain(next.newIntents, true /* resume */));
}
// Well the app will no longer be stopped.
// Clear app token stopped state in window manager if needed.
next.notifyAppResumed(next.stopped);
EventLogTags.writeWmResumeActivity(next.mUserId, System.identityHashCode(next),
next.getTask().mTaskId, next.shortComponentName);
mAtmService.getAppWarningsLocked().onResumeActivity(next);
next.app.setPendingUiCleanAndForceProcessStateUpTo(mAtmService.mTopProcessState);
next.abortAndClearOptionsAnimation();
transaction.setLifecycleStateRequest(
ResumeActivityItem.obtain(next.app.getReportedProcState(),
dc.isNextTransitionForward()));
mAtmService.getLifecycleManager().scheduleTransaction(transaction);
ProtoLog.d(WM_DEBUG_STATES, "resumeTopActivity: Resumed %s", next);
} catch (Exception e) {
// Whoops, need to restart this activity!
ProtoLog.v(WM_DEBUG_STATES, "Resume failed; resetting state to %s: "
+ "%s", lastState, next);
next.setState(lastState, "resumeTopActivityInnerLocked");
// lastResumedActivity being non-null implies there is a lastStack present.
if (lastResumedActivity != null) {
lastResumedActivity.setState(RESUMED, "resumeTopActivityInnerLocked");
}
Slog.i(TAG, "Restarting because process died: " + next);
if (!next.hasBeenLaunched) {
next.hasBeenLaunched = true;
} else if (SHOW_APP_STARTING_PREVIEW && lastFocusedRootTask != null
&& lastFocusedRootTask.isTopRootTaskInDisplayArea()) {
next.showStartingWindow(false /* taskSwitch */);
}
mTaskSupervisor.startSpecificActivity(next, true, false);
return true;
}
// From this point on, if something goes wrong there is no way
// to recover the activity.
try {
next.completeResumeLocked();
} catch (Exception e) {
// If any exception gets thrown, toss away this
// activity and try the next one.
Slog.w(TAG, "Exception thrown during resume of " + next, e);
next.finishIfPossible("resume-exception", true /* oomAdj */);
return true;
}
} else {
// Whoops, need to restart this activity!
if (!next.hasBeenLaunched) {
next.hasBeenLaunched = true;
} else {
if (SHOW_APP_STARTING_PREVIEW) {
next.showStartingWindow(false /* taskSwich */);
}
if (DEBUG_SWITCH) Slog.v(TAG_SWITCH, "Restarting: " + next);
}
ProtoLog.d(WM_DEBUG_STATES, "resumeTopActivity: Restarting %s", next);
mTaskSupervisor.startSpecificActivity(next, true, true);
}
return true;
}
- 首先判断mResumedActivity是否为空，如果不为空，那么说明当前存在Activity在前台展示，其实就是sourceRecord源Activity，所以这时会执行startPausing方法，将当前Activity的生命周期更新为Pause。
void schedulePauseActivity(ActivityRecord prev, boolean userLeaving,
boolean pauseImmediately, String reason) {
ProtoLog.v(WM_DEBUG_STATES, "Enqueueing pending pause: %s", prev);
try {
EventLogTags.writeWmPauseActivity(prev.mUserId, System.identityHashCode(prev),
prev.shortComponentName, "userLeaving=" + userLeaving, reason);
mAtmService.getLifecycleManager().scheduleTransaction(prev.app.getThread(),
prev.appToken, PauseActivityItem.obtain(prev.finishing, userLeaving,
prev.configChangeFlags, pauseImmediately));
} catch (Exception e) {
// Ignore exception, if process died other code will cleanup.
Slog.w(TAG, "Exception thrown during pause", e);
mPausingActivity = null;
mLastPausedActivity = null;
mTaskSupervisor.mNoHistoryActivities.remove(prev);
}
}
在startPausing方法中，会通过ATMS向App进程发送消息，将Activity的生命周期置为Pause。
- 判断当前要启动的Activity是否与当前app进程绑定，是通过attachedToProcess方法判断，如果进程存在，那么就直接封装ClientTransaction进行app通信；如果进程不存在，例如点击Launcher icon启动Activity，那么就会调用ActivityTaskSupervsor的startSpecificActivity启动Activity。
ActivityTaskSupervsor # startSpecificActivity
注意从上传下来的参数，andResume = true，checkConfig = true。
void startSpecificActivity(ActivityRecord r, boolean andResume, boolean checkConfig) {
// Is this activity's application already running?
final WindowProcessController wpc =
mService.getProcessController(r.processName, r.info.applicationInfo.uid);
boolean knownToBeDead = false;
// 进程已经创建
if (wpc != null && wpc.hasThread()) {
try {
realStartActivityLocked(r, wpc, 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.
knownToBeDead = true;
}
r.notifyUnknownVisibilityLaunchedForKeyguardTransition();
final boolean isTop = andResume && r.isTopRunningActivity();
// 再次创建一个app进程
mService.startProcessAsync(r, knownToBeDead, isTop, isTop ? "top-activity" : "activity");
}
ActivityTaskSupervisor # realStartActivityLocked
boolean realStartActivityLocked(ActivityRecord r, WindowProcessController proc,
boolean andResume, boolean checkConfig) throws RemoteException {
// ......
try {
// ......
try {
// ......
// Create activity launch transaction.
//创建与APP通信的ClientTransaction事务
final ClientTransaction clientTransaction = ClientTransaction.obtain(
proc.getThread(), r.appToken);
final boolean isTransitionForward = r.isTransitionForward();
//往callback中添加LaunchActivityItem
clientTransaction.addCallback(LaunchActivityItem.obtain(new Intent(r.intent),
System.identityHashCode(r), r.info,
// TODO: Have this take the merged configuration instead of separate global
// and override configs.
mergedConfiguration.getGlobalConfiguration(),
mergedConfiguration.getOverrideConfiguration(), r.compat,
r.getFilteredReferrer(r.launchedFromPackage), task.voiceInteractor,
proc.getReportedProcState(), r.getSavedState(), r.getPersistentSavedState(),
results, newIntents, r.takeOptions(), isTransitionForward,
proc.createProfilerInfoIfNeeded(), r.assistToken, activityClientController,
r.createFixedRotationAdjustmentsIfNeeded(), r.shareableActivityToken,
r.getLaunchedFromBubble()));
// Set desired final state.
final ActivityLifecycleItem lifecycleItem;
if (andResume) {
lifecycleItem = ResumeActivityItem.obtain(isTransitionForward);
} else {
lifecycleItem = PauseActivityItem.obtain();
}
//添加ResumeActivityItem
clientTransaction.setLifecycleStateRequest(lifecycleItem);
// Schedule transaction.
//执行事务
mService.getLifecycleManager().scheduleTransaction(clientTransaction);
// ......
} catch (RemoteException e) {
// ......
} finally {
endDeferResume();
proc.resumeConfigurationDispatch();
}
//......
return true;
}
总结流程图：
1.3 APP通信流程分析
当执行ActivityTaskSupervisor的realStartActivityLocked方法时，就开启建立与App通信的事务，就是创建一个ClientTransaction。
public void addCallback(ClientTransactionItem activityCallback) {
if (mActivityCallbacks == null) {
mActivityCallbacks = new ArrayList<>();
}
mActivityCallbacks.add(activityCallback);
}
其中有几个核心方法，我们着重看下，首先是addCallback方法，可以传入一个ClientTransactionItem对象，所有传入的对象都放在mActivityCallbacks集合中，例如LaunchActivityItem，用于发起创建Activity的请求。
public void setLifecycleStateRequest(ActivityLifecycleItem stateRequest) {
mLifecycleStateRequest = stateRequest;
}
setLifecycleStateRequest方法，用于设置生命周期的请求，当前启动的Activity生命周期要到哪个生命周期方法，例如ResumeActivityItem。
当创建完成ClientTransaction之后，就会调用ATMS中ClientLifecycleManager执行事务，其实最终执行的就是App的scheduleTransaction方法，传值就是ClientTransaction对象。
ClientTransaction # scheduleTransaction
public void schedule() throws RemoteException {
mClient.scheduleTransaction(this);
}
ClientTransactionHandler # scheduleTransaction
void scheduleTransaction(ClientTransaction transaction) {
transaction.preExecute(this);
sendMessage(ActivityThread.H.EXECUTE_TRANSACTION, transaction);
}
我们看到，进入APP进程之后，就是通过Handler来发送消息，看下EXECUTE_TRANSACTION这个key对应的处理方式。
case EXECUTE_TRANSACTION:
final ClientTransaction transaction = (ClientTransaction) msg.obj;
mTransactionExecutor.execute(transaction);
if (isSystem()) {
// Client transactions inside system process are recycled on the client side
// instead of ClientLifecycleManager to avoid being cleared before this
// message is handled.
transaction.recycle();
}
// TODO(lifecycler): Recycle locally scheduled transactions.
break;
TransactionExecutor # execute
public void execute(ClientTransaction transaction) {
if (DEBUG_RESOLVER) Slog.d(TAG, tId(transaction) + "Start resolving transaction");
// ......
if (DEBUG_RESOLVER) Slog.d(TAG, transactionToString(transaction, mTransactionHandler));
executeCallbacks(transaction);
executeLifecycleState(transaction);
mPendingActions.clear();
if (DEBUG_RESOLVER) Slog.d(TAG, tId(transaction) + "End resolving transaction");
}
所以在执行execute方法时，有两个重要的方法，分别是executeCallbacks和executeLifecycleState，从这两个方法名我们就能知道，其实就是在创建ClientTransaction时，通过addCallback以及setLifecycleStateRequest方法设置的值。
TransactionExecutor # executeCallbacks
public void executeCallbacks(ClientTransaction transaction) {
final List<ClientTransactionItem> callbacks = transaction.getCallbacks();
if (callbacks == null || callbacks.isEmpty()) {
// No callbacks to execute, return early.
return;
}
// ......
final int size = callbacks.size();
for (int i = 0; i < size; ++i) {
final ClientTransactionItem item = callbacks.get(i);
// ......
//执行ClientTransactionItem的execute函数
item.execute(mTransactionHandler, token, mPendingActions);
item.postExecute(mTransactionHandler, token, mPendingActions);
if (r == null) {
// Launch activity request will create an activity record.
r = mTransactionHandler.getActivityClient(token);
}
if (postExecutionState != UNDEFINED && r != null) {
// Skip the very last transition and perform it by explicit state request instead.
final boolean shouldExcludeLastTransition =
i == lastCallbackRequestingState && finalState == postExecutionState;
cycleToPath(r, postExecutionState, shouldExcludeLastTransition, transaction);
}
}
}
首先在executeCallbacks方法中，是拿到了在创建ClientTransaction时传入的全部Callback，并遍历全部，其实就传入了1个LaunchActivityItem，因此就会执行其execute方法，所以看下方法内部实现。
LaunchActivityItem # execute
@Override
public void execute(ClientTransactionHandler client, IBinder token,
PendingTransactionActions pendingActions) {
Trace.traceBegin(TRACE_TAG_ACTIVITY_MANAGER, "activityStart");
ActivityClientRecord r = client.getLaunchingActivity(token);
client.handleLaunchActivity(r, pendingActions, null /* customIntent */);
Trace.traceEnd(TRACE_TAG_ACTIVITY_MANAGER);
}
在这个方法中，最终执行了ClientTransactionHandler的handleLaunchActivity方法，这个类我们在前面见到过，就是执行scheduleTransaction方法时，通过Handler发送了消息，但是我们去看代码时，发现这个方法是一个抽象方法，因为ActivityThread也实现了ClientTransactionHandler，所以去子类看实现。
ActivityThread # handleLaunchActivity
public Activity handleLaunchActivity(ActivityClientRecord r,
PendingTransactionActions pendingActions, Intent customIntent) {
// ......
final Activity a = performLaunchActivity(r, customIntent);
if (a != null) {
r.createdConfig = new Configuration(mConfigurationController.getConfiguration());
reportSizeConfigurations(r);
if (!r.activity.mFinished && pendingActions != null) {
pendingActions.setOldState(r.state);
pendingActions.setRestoreInstanceState(true);
pendingActions.setCallOnPostCreate(true);
}
} else {
// If there was an error, for any reason, tell the activity manager to stop us.
ActivityClient.getInstance().finishActivity(r.token, Activity.RESULT_CANCELED,
null /* resultData */, Activity.DONT_FINISH_TASK_WITH_ACTIVITY);
}
return a;
}
在ActivityThread的handleLaunchActivity方法中，是调用了performLaunchActivity方法，这个方法是Activity启动的核心实现。
ActivityThread # performLaunchActivity
private Activity performLaunchActivity(ActivityClientRecord r, Intent customIntent) {
ActivityInfo aInfo = r.activityInfo;
if (r.packageInfo == null) {
r.packageInfo = getPackageInfo(aInfo.applicationInfo, r.compatInfo,
Context.CONTEXT_INCLUDE_CODE);
}
ComponentName component = r.intent.getComponent();
if (component == null) {
component = r.intent.resolveActivity(
mInitialApplication.getPackageManager());
r.intent.setComponent(component);
}
if (r.activityInfo.targetActivity != null) {
component = new ComponentName(r.activityInfo.packageName,
r.activityInfo.targetActivity);
}
ContextImpl appContext = createBaseContextForActivity(r);
Activity activity = null;
try {
java.lang.ClassLoader cl = appContext.getClassLoader();
//通过反射的方式创建Activity
activity = mInstrumentation.newActivity(
cl, component.getClassName(), r.intent);
StrictMode.incrementExpectedActivityCount(activity.getClass());
r.intent.setExtrasClassLoader(cl);
r.intent.prepareToEnterProcess(isProtectedComponent(r.activityInfo),
appContext.getAttributionSource());
if (r.state != null) {
r.state.setClassLoader(cl);
}
} catch (Exception e) {
if (!mInstrumentation.onException(activity, e)) {
throw new RuntimeException(
"Unable to instantiate activity " + component
+ ": " + e.toString(), e);
}
}
try {
Application app = r.packageInfo.makeApplication(false, mInstrumentation);
if (localLOGV) Slog.v(TAG, "Performing launch of " + r);
if (localLOGV) Slog.v(
TAG, r + ": app=" + app
+ ", appName=" + app.getPackageName()
+ ", pkg=" + r.packageInfo.getPackageName()
+ ", comp=" + r.intent.getComponent().toShortString()
+ ", dir=" + r.packageInfo.getAppDir());
// updatePendingActivityConfiguration() reads from mActivities to update
// ActivityClientRecord which runs in a different thread. Protect modifications to
// mActivities to avoid race.
synchronized (mResourcesManager) {
mActivities.put(r.token, r);
}
if (activity != null) {
CharSequence title = r.activityInfo.loadLabel(appContext.getPackageManager());
Configuration config =
new Configuration(mConfigurationController.getCompatConfiguration());
if (r.overrideConfig != null) {
config.updateFrom(r.overrideConfig);
}
if (DEBUG_CONFIGURATION) Slog.v(TAG, "Launching activity "
+ r.activityInfo.name + " with config " + config);
Window window = null;
if (r.mPendingRemoveWindow != null && r.mPreserveWindow) {
window = r.mPendingRemoveWindow;
r.mPendingRemoveWindow = null;
r.mPendingRemoveWindowManager = null;
}
// Activity resources must be initialized with the same loaders as the
// application context.
appContext.getResources().addLoaders(
app.getResources().getLoaders().toArray(new ResourcesLoader[0]));
appContext.setOuterContext(activity);
//与窗口绑定 WMS相关内容
activity.attach(appContext, this, getInstrumentation(), r.token,
r.ident, app, r.intent, r.activityInfo, title, r.parent,
r.embeddedID, r.lastNonConfigurationInstances, config,
r.referrer, r.voiceInteractor, window, r.configCallback,
r.assistToken, r.shareableActivityToken);
if (customIntent != null) {
activity.mIntent = customIntent;
}
r.lastNonConfigurationInstances = null;
checkAndBlockForNetworkAccess();
activity.mStartedActivity = false;
int theme = r.activityInfo.getThemeResource();
//设置属性
if (theme != 0) {
activity.setTheme(theme);
}
if (r.mActivityOptions != null) {
activity.mPendingOptions = r.mActivityOptions;
r.mActivityOptions = null;
}
activity.mLaunchedFromBubble = r.mLaunchedFromBubble;
activity.mCalled = false;
// Assigning the activity to the record before calling onCreate() allows
// ActivityThread#getActivity() lookup for the callbacks triggered from
// ActivityLifecycleCallbacks#onActivityCreated() or
// ActivityLifecycleCallback#onActivityPostCreated().
r.activity = activity;
if (r.isPersistable()) {
//执行Activity的onCreate方法
mInstrumentation.callActivityOnCreate(activity, r.state, r.persistentState);
} else {
mInstrumentation.callActivityOnCreate(activity, r.state);
}
if (!activity.mCalled) {
throw new SuperNotCalledException(
"Activity " + r.intent.getComponent().toShortString() +
" did not call through to super.onCreate()");
}
mLastReportedWindowingMode.put(activity.getActivityToken(),
config.windowConfiguration.getWindowingMode());
}
r.setState(ON_CREATE);
} catch (SuperNotCalledException e) {
throw e;
} catch (Exception e) {
if (!mInstrumentation.onException(activity, e)) {
throw new RuntimeException(
"Unable to start activity " + component
+ ": " + e.toString(), e);
}
}
return activity;
}
这个方法比较重要，我们来分析一下主要干了什么事：
- 通过Instrumentation来创建了一个Activity，是采用反射的方式；
- 调用Activity的attach方法，在这个方法中会创建Activity的PhoneWindow，然后与对应的WindowManager绑定；
- 为Activity添加theme主题；
- 通过Instrumentation调用Activity的onCreate方法，进入生命周期同步的流程。
这样，其实Activity的窗口就算是创建完成，executeCallbacks方法也算是执行结束了，此时就会返回已经绑定到窗口的Activity，接下来看下executeLifecycleState方法。
TransactionExecutor # executeLifecycleState
private void executeLifecycleState(ClientTransaction transaction) {
final ActivityLifecycleItem lifecycleItem = transaction.getLifecycleStateRequest();
if (lifecycleItem == null) {
// No lifecycle request, return early.
return;
}
final IBinder token = transaction.getActivityToken();
final ActivityClientRecord r = mTransactionHandler.getActivityClient(token);
if (DEBUG_RESOLVER) {
Slog.d(TAG, tId(transaction) + "Resolving lifecycle state: "
+ lifecycleItem + " for activity: "
+ getShortActivityName(token, mTransactionHandler));
}
if (r == null) {
// Ignore requests for non-existent client records for now.
return;
}
// Cycle to the state right before the final requested state.
//同步到最终的请求状态之前
cycleToPath(r, lifecycleItem.getTargetState(), true /* excludeLastState */, transaction);
// Execute the final transition with proper parameters.
lifecycleItem.execute(mTransactionHandler, token, mPendingActions);
lifecycleItem.postExecute(mTransactionHandler, token, mPendingActions);
}
这里其实就是拿到创建ClientTransaction时传入的ActivityLifecycleItem，也就是ResumeActivityItem。因为现在Activity的状态是ON_CREATE，但是期望状态是ON_RESUME，因此首先调用cycleToPath方法，进行生命周期同步，同步到最终的请求状态之前，也就是ON_START。
最后执行ResumeActivityItem的execute方法。
ResumeActivityItem # execute
@Override
public void execute(ClientTransactionHandler client, ActivityClientRecord r,
PendingTransactionActions pendingActions) {
Trace.traceBegin(TRACE_TAG_ACTIVITY_MANAGER, "activityResume");
client.handleResumeActivity(r, true /* finalStateRequest */, mIsForward,
"RESUME_ACTIVITY");
Trace.traceEnd(TRACE_TAG_ACTIVITY_MANAGER);
}
这个方法其实跟LaunchActivityItem类似，其实最终还是执行ActivityThread的handleResumeActivity方法，在这个方法中，会将Activity的生命周期置为ON_RESUME，那么这个Activity就已经处于前台可交互的状态了。
所以从我们应用层发起启动Activity的请求，到最终Activity展示在页面上，就需要如上三步：
- 在ATMS层，会对启动Activity任务做意图解析，并创建对应的ActivityRecord，这里主要是通过ActivityStarter来进行管理，将其封装成一个Request，最终执行这个Request；
- 既然要启动一个Activity，肯定需要对任务栈进行管理，尤其是新起的Activity，要判断它的启动模式，以及源Activity所在的任务栈，看是否需要和源Activity在同一任务栈，还是需要新起一个任务栈；然后需要对FocusTasks做处理，对于源Activity需要将其生命周期设置为Pause，然后判断当前app进程是否存在，如果不存在，那么就会调用ActivitySupervisor的startSpecificActivity方法进行Activity创建。
- 最终还是调用ActivitySupervisor的realStartActivityLocked方法，这个时候就会建立与app通信的基础，创建ClientTransaction对象，设置LaunchActivityItem callback以及ResumeACtivityItem lifeCycleStateRequest，调用ActivityThread的scheduleTransaction方法。
- 在ActivityThread的scheduleTransaction方法，其实就是通过Handler发送消息，ActivityThread.H.EXECUTE_TRANSACTION，在这里就会执行TransactionExecutor的execute方法进行事务数据的解析，分别执行LaunchActivityItem的execute方法，目的为了创建新的Activity以及绑定Activity到WindowManager上；然后再执行ResumeACtivityItem的execute方法，将生命周期同步到ON_RESUME。
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