Android系统应用框架篇：Activity启动流程(三)
Android系统应用框架篇：Activity启动流程(三)
作者: 郭孝星
邮箱: [email protected]
博客: http://blog.csdn.net/allenwells
简书: http://www.jianshu.com/users/66a47e04215b/latest_articles
关于作者
郭孝星，非著名程序员，代码洁癖患者，爱编程，好吉他，喜烹饪，爱一切有趣的事物和人。
关于文章
作者的文章会同时发布在Github、CSDN与简书上, 文章顶部也会附上文章的Github链接。如果文章中有
什么疑问也欢迎发邮件与我交流, 对于交流的问题, 请描述清楚问题并附上代码与日志, 一般都会给予回复。
如果文章中有什么错误, 也欢迎斧正。如果你觉得本文章对你有所帮助, 也欢迎去star文章, 关注文章的最新
的动态。另外建议大家去Github上浏览文章，一方面文章的写作都是在Github上进行的，所以Github上的
更新是最及时的，另一方面感觉Github对Markdown的支持更好，文章的渲染也更加美观。
第一次阅览本系列文章，请参见导读，更多文章请参见文章目录。
- 5Android系统应用框架篇：Activity启动流程(一)
- 6Android系统应用框架篇：Activity启动流程(二)
- 7Android系统应用框架篇：Activity启动流程(三)
我们接着上一篇文章来继续分析Activity的启动流程。
Activity启动流程序列图
Activity启动流程结构图
18 ActivityManagerService.activityPaused(IBinder token, Bundle icicle)
public final class ActivityManagerService extends ActivityManagerNative
implements Watchdog.Monitor, BatteryStatsImpl.BatteryCallback{
public final void activityPaused(IBinder token, Bundle icicle) {
// Refuse possible leaked file descriptors
if (icicle != null && icicle.hasFileDescriptors()) {
throw new IllegalArgumentException("File descriptors passed in Bundle");
}
final long origId = Binder.clearCallingIdentity();
mMainStack.activityPaused(token, icicle, false);
Binder.restoreCallingIdentity(origId);
}
}IBinder token还是跟前面一样指向ActivityManagerService中与Launcher组件对应的一个ActivityRecord对象。该函数会调用ActivityStack.activityPaused()方法
进一步就处理ACTIVITY_PAUSED_TRANSACTION进程通信请求。
19 ActivityStack.activityPaused(IBinder token, Bundle icicle, boolean timeout)
public class ActivityStack {
final ActivityManagerService mService;
final void activityPaused(IBinder token, Bundle icicle, boolean timeout) {
if (DEBUG_PAUSE) Slog.v(
TAG, "Activity paused: token=" + token + ", icicle=" + icicle
+ ", timeout=" + timeout);
ActivityRecord r = null;
synchronized (mService) {
int index = indexOfTokenLocked(token);
if (index >= 0) {
//根据token查找mHistory栈中对应的ActivityRecord对象
r = (ActivityRecord)mHistory.get(index);
if (!timeout) {
r.icicle = icicle;
r.haveState = true;
}
//移除PAUSE_TIMEOUT_MSG消息，因为Launcher组件已经在规定的时间内完成ActivityManagerService给
//它发送的终止通知了。
mHandler.removeMessages(PAUSE_TIMEOUT_MSG, r);
if (mPausingActivity == r) {
//此时r与mPausingActivity指向的都是Launcher对应的ActivityRecord对象。把Launcher置为
//ActivityState.PAUSED状态。
r.state = ActivityState.PAUSED;
//执行目标Activity的启动操作
completePauseLocked();
} else {
EventLog.writeEvent(EventLogTags.AM_FAILED_TO_PAUSE,
System.identityHashCode(r), r.shortComponentName,
mPausingActivity != null
? mPausingActivity.shortComponentName : "(none)");
}
}
}
}
}该函数执行了以下操作：
1 根据token查找mHistory栈中对应的ActivityRecord对象。
2 移除PAUSE_TIMEOUT_MSG消息，因为Launcher组件已经在规定的时间内完成ActivityManagerService给它发送的终止通知了。
3 把Launcher置为ActivityState.PAUSED状态。
4 调用completePauseLocked()，执行目标Activity的启动操作。20 ActivityStack.completePauseLocked()
public class ActivityStack{
private final void completePauseLocked() {
ActivityRecord prev = mPausingActivity;
if (DEBUG_PAUSE) Slog.v(TAG, "Complete pause: " + prev);
if (prev != null) {
if (prev.finishing) {
if (DEBUG_PAUSE) Slog.v(TAG, "Executing finish of activity: " + prev);
prev = finishCurrentActivityLocked(prev, FINISH_AFTER_VISIBLE);
} else if (prev.app != null) {
if (DEBUG_PAUSE) Slog.v(TAG, "Enqueueing pending stop: " + prev);
if (prev.waitingVisible) {
prev.waitingVisible = false;
mWaitingVisibleActivities.remove(prev);
if (DEBUG_SWITCH || DEBUG_PAUSE) Slog.v(
TAG, "Complete pause, no longer waiting: " + prev);
}
if (prev.configDestroy) {
// The previous is being paused because the configuration
// is changing, which means it is actually stopping...
// To juggle the fact that we are also starting a new
// instance right now, we need to first completely stop
// the current instance before starting the new one.
if (DEBUG_PAUSE) Slog.v(TAG, "Destroying after pause: " + prev);
destroyActivityLocked(prev, true);
} else {
mStoppingActivities.add(prev);
if (mStoppingActivities.size() > 3) {
// If we already have a few activities waiting to stop,
// then give up on things going idle and start clearing
// them out.
if (DEBUG_PAUSE) Slog.v(TAG, "To many pending stops, forcing idle");
Message msg = Message.obtain();
msg.what = IDLE_NOW_MSG;
mHandler.sendMessage(msg);
}
}
} else {
if (DEBUG_PAUSE) Slog.v(TAG, "App died during pause, not stopping: " + prev);
prev = null;
}
//mPausingActivity置为null，表示当前正在终止的Activity组件已经进入Paused状态了。
mPausingActivity = null;
}
if (!mService.mSleeping && !mService.mShuttingDown) {
//如果系统没有处于睡眠或关闭状态，则启动位于栈顶的Activity组件。
resumeTopActivityLocked(prev);
} else {
if (mGoingToSleep.isHeld()) {
mGoingToSleep.release();
}
if (mService.mShuttingDown) {
mService.notifyAll();
}
}
if (prev != null) {
prev.resumeKeyDispatchingLocked();
}
if (prev.app != null && prev.cpuTimeAtResume > 0
&& mService.mBatteryStatsService.isOnBattery()) {
long diff = 0;
synchronized (mService.mProcessStatsThread) {
diff = mService.mProcessStats.getCpuTimeForPid(prev.app.pid)
- prev.cpuTimeAtResume;
}
if (diff > 0) {
BatteryStatsImpl bsi = mService.mBatteryStatsService.getActiveStatistics();
synchronized (bsi) {
BatteryStatsImpl.Uid.Proc ps =
bsi.getProcessStatsLocked(prev.info.applicationInfo.uid,
prev.info.packageName);
if (ps != null) {
ps.addForegroundTimeLocked(diff);
}
}
}
}
prev.cpuTimeAtResume = 0; // reset it
}
}
mPausingActivity置为null，表示当前正在终止的Activity组件已经进入Paused状态了，调用resumeTopActivityLocked(prev)启动位于栈顶的Activity组件。
21 ActivityStack.resumeTopActivityLocked(ActivityRecord prev)
public class ActivityStack{
/**
* Ensure that the top activity in the stack is resumed.
*
* @param prev The previously resumed activity, for when in the process
* of pausing; can be null to call from elsewhere.
*
* @return Returns true if something is being resumed, or false if
* nothing happened.
*/
final boolean resumeTopActivityLocked(ActivityRecord prev) {
//栈顶Activity，它指向即将启动的目标Activity组件
// Find the first activity that is not finishing.
ActivityRecord next = topRunningActivityLocked(null);
// Remember how we'll process this pause/resume situation, and ensure
// that the state is reset however we wind up proceeding.
final boolean userLeaving = mUserLeaving;
mUserLeaving = false;
if (next == null) {
// There are no more activities! Let's just start up the
// Launcher...
if (mMainStack) {
return mService.startHomeActivityLocked();
}
}
next.delayedResume = false;
// If the top activity is the resumed one, nothing to do.
if (mResumedActivity == next && next.state == ActivityState.RESUMED) {
// Make sure we have executed any pending transitions, since there
// should be nothing left to do at this point.
mService.mWindowManager.executeAppTransition();
mNoAnimActivities.clear();
return false;
}
// If we are sleeping, and there is no resumed activity, and the top
// activity is paused, well that is the state we want.
if ((mService.mSleeping || mService.mShuttingDown)
&& mLastPausedActivity == next && next.state == ActivityState.PAUSED) {
// Make sure we have executed any pending transitions, since there
// should be nothing left to do at this point.
mService.mWindowManager.executeAppTransition();
mNoAnimActivities.clear();
return false;
}
// The activity may be waiting for stop, but that is no longer
// appropriate for it.
mStoppingActivities.remove(next);
mWaitingVisibleActivities.remove(next);
if (DEBUG_SWITCH) Slog.v(TAG, "Resuming " + next);
//上一步中已经将mPausingActivity置为null
// If we are currently pausing an activity, then don't do anything
// until that is done.
if (mPausingActivity != null) {
if (DEBUG_SWITCH) Slog.v(TAG, "Skip resume: pausing=" + mPausingActivity);
return false;
}
// Okay we are now going to start a switch, to 'next'. We may first
// have to pause the current activity, but this is an important point
// where we have decided to go to 'next' so keep track of that.
// XXX "App Redirected" dialog is getting too many false positives
// at this point, so turn off for now.
if (false) {
if (mLastStartedActivity != null && !mLastStartedActivity.finishing) {
long now = SystemClock.uptimeMillis();
final boolean inTime = mLastStartedActivity.startTime != 0
&& (mLastStartedActivity.startTime + START_WARN_TIME) >= now;
final int lastUid = mLastStartedActivity.info.applicationInfo.uid;
final int nextUid = next.info.applicationInfo.uid;
if (inTime && lastUid != nextUid
&& lastUid != next.launchedFromUid
&& mService.checkPermission(
android.Manifest.permission.STOP_APP_SWITCHES,
-1, next.launchedFromUid)
!= PackageManager.PERMISSION_GRANTED) {
mService.showLaunchWarningLocked(mLastStartedActivity, next);
} else {
next.startTime = now;
mLastStartedActivity = next;
}
} else {
next.startTime = SystemClock.uptimeMillis();
mLastStartedActivity = next;
}
}
// We need to start pausing the current activity so the top one
// can be resumed...
if (mResumedActivity != null) {
if (DEBUG_SWITCH) Slog.v(TAG, "Skip resume: need to start pausing");
startPausingLocked(userLeaving, false);
return true;
}
if (prev != null && prev != next) {
if (!prev.waitingVisible && next != null && !next.nowVisible) {
prev.waitingVisible = true;
mWaitingVisibleActivities.add(prev);
if (DEBUG_SWITCH) Slog.v(
TAG, "Resuming top, waiting visible to hide: " + prev);
} else {
// The next activity is already visible, so hide the previous
// activity's windows right now so we can show the new one ASAP.
// We only do this if the previous is finishing, which should mean
// it is on top of the one being resumed so hiding it quickly
// is good. Otherwise, we want to do the normal route of allowing
// the resumed activity to be shown so we can decide if the
// previous should actually be hidden depending on whether the
// new one is found to be full-screen or not.
if (prev.finishing) {
mService.mWindowManager.setAppVisibility(prev, false);
if (DEBUG_SWITCH) Slog.v(TAG, "Not waiting for visible to hide: "
+ prev + ", waitingVisible="
+ (prev != null ? prev.waitingVisible : null)
+ ", nowVisible=" + next.nowVisible);
} else {
if (DEBUG_SWITCH) Slog.v(TAG, "Previous already visible but still waiting to hide: "
+ prev + ", waitingVisible="
+ (prev != null ? prev.waitingVisible : null)
+ ", nowVisible=" + next.nowVisible);
}
}
}
// We are starting up the next activity, so tell the window manager
// that the previous one will be hidden soon. This way it can know
// to ignore it when computing the desired screen orientation.
if (prev != null) {
if (prev.finishing) {
if (DEBUG_TRANSITION) Slog.v(TAG,
"Prepare close transition: prev=" + prev);
if (mNoAnimActivities.contains(prev)) {
mService.mWindowManager.prepareAppTransition(WindowManagerPolicy.TRANSIT_NONE);
} else {
mService.mWindowManager.prepareAppTransition(prev.task == next.task
? WindowManagerPolicy.TRANSIT_ACTIVITY_CLOSE
: WindowManagerPolicy.TRANSIT_TASK_CLOSE);
}
mService.mWindowManager.setAppWillBeHidden(prev);
mService.mWindowManager.setAppVisibility(prev, false);
} else {
if (DEBUG_TRANSITION) Slog.v(TAG,
"Prepare open transition: prev=" + prev);
if (mNoAnimActivities.contains(next)) {
mService.mWindowManager.prepareAppTransition(WindowManagerPolicy.TRANSIT_NONE);
} else {
mService.mWindowManager.prepareAppTransition(prev.task == next.task
? WindowManagerPolicy.TRANSIT_ACTIVITY_OPEN
: WindowManagerPolicy.TRANSIT_TASK_OPEN);
}
}
if (false) {
mService.mWindowManager.setAppWillBeHidden(prev);
mService.mWindowManager.setAppVisibility(prev, false);
}
} else if (mHistory.size() > 1) {
if (DEBUG_TRANSITION) Slog.v(TAG,
"Prepare open transition: no previous");
if (mNoAnimActivities.contains(next)) {
mService.mWindowManager.prepareAppTransition(WindowManagerPolicy.TRANSIT_NONE);
} else {
mService.mWindowManager.prepareAppTransition(WindowManagerPolicy.TRANSIT_ACTIVITY_OPEN);
}
}
if (next.app != null && next.app.thread != null) {
if (DEBUG_SWITCH) Slog.v(TAG, "Resume running: " + next);
// This activity is now becoming visible.
mService.mWindowManager.setAppVisibility(next, true);
ActivityRecord lastResumedActivity = mResumedActivity;
ActivityState lastState = next.state;
mService.updateCpuStats();
next.state = ActivityState.RESUMED;
mResumedActivity = next;
next.task.touchActiveTime();
mService.updateLruProcessLocked(next.app, true, true);
updateLRUListLocked(next);
// Have the window manager re-evaluate the orientation of
// the screen based on the new activity order.
boolean updated = false;
if (mMainStack) {
synchronized (mService) {
Configuration config = mService.mWindowManager.updateOrientationFromAppTokens(
mService.mConfiguration,
next.mayFreezeScreenLocked(next.app) ? next : null);
if (config != null) {
next.frozenBeforeDestroy = true;
}
updated = mService.updateConfigurationLocked(config, next);
}
}
if (!updated) {
// 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 = topRunningActivityLocked(null);
if (DEBUG_SWITCH) Slog.i(TAG,
"Activity config changed during resume: " + next
+ ", new next: " + nextNext);
if (nextNext != next) {
// Do over!
mHandler.sendEmptyMessage(RESUME_TOP_ACTIVITY_MSG);
}
if (mMainStack) {
mService.setFocusedActivityLocked(next);
}
ensureActivitiesVisibleLocked(null, 0);
mService.mWindowManager.executeAppTransition();
mNoAnimActivities.clear();
return true;
}
try {
// Deliver all pending results.
ArrayList a = next.results;
if (a != null) {
final int N = a.size();
if (!next.finishing && N > 0) {
if (DEBUG_RESULTS) Slog.v(
TAG, "Delivering results to " + next
+ ": " + a);
next.app.thread.scheduleSendResult(next, a);
}
}
if (next.newIntents != null) {
next.app.thread.scheduleNewIntent(next.newIntents, next);
}
EventLog.writeEvent(EventLogTags.AM_RESUME_ACTIVITY,
System.identityHashCode(next),
next.task.taskId, next.shortComponentName);
next.app.thread.scheduleResumeActivity(next,
mService.isNextTransitionForward());
pauseIfSleepingLocked();
} catch (Exception e) {
// Whoops, need to restart this activity!
next.state = lastState;
mResumedActivity = lastResumedActivity;
Slog.i(TAG, "Restarting because process died: " + next);
if (!next.hasBeenLaunched) {
next.hasBeenLaunched = true;
} else {
if (SHOW_APP_STARTING_PREVIEW && mMainStack) {
mService.mWindowManager.setAppStartingWindow(
next, next.packageName, next.theme,
next.nonLocalizedLabel,
next.labelRes, next.icon, null, true);
}
}
//执行目标Activity启动操作。
startSpecificActivityLocked(next, true, false);
return true;
}
// From this point on, if something goes wrong there is no way
// to recover the activity.
try {
next.visible = true;
completeResumeLocked(next);
} 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);
requestFinishActivityLocked(next, Activity.RESULT_CANCELED, null,
"resume-exception");
return true;
}
// Didn't need to use the icicle, and it is now out of date.
next.icicle = null;
next.haveState = false;
next.stopped = false;
} else {
// Whoops, need to restart this activity!
if (!next.hasBeenLaunched) {
next.hasBeenLaunched = true;
} else {
if (SHOW_APP_STARTING_PREVIEW) {
mService.mWindowManager.setAppStartingWindow(
next, next.packageName, next.theme,
next.nonLocalizedLabel,
next.labelRes, next.icon, null, true);
}
if (DEBUG_SWITCH) Slog.v(TAG, "Restarting: " + next);
}
startSpecificActivityLocked(next, true, true);
}
return true;
}
}在第10步中，ActivityManagerService已经尝试调用ActivityManagerService.resumeTopActivityLocked()来启动目标Activity组件了，但是
那个时候Launcher组件尚未进入Paused状态（即ActivityStack.mResumedActivity != null）所以先调用ActivityManagerService.startPausingLocked()
来终止Launcher组件。
接下来调用startSpecificActivityLocked(next, true, false)，执行目标Activity启动操作。
22 ActivityStack.startSpecificActivityLocked(ActivityRecord r, boolean andResume, boolean checkConfig)
public class ActivityStack{
private final 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);
if (r.launchTime == 0) {
r.launchTime = SystemClock.uptimeMillis();
if (mInitialStartTime == 0) {
mInitialStartTime = r.launchTime;
}
} else if (mInitialStartTime == 0) {
mInitialStartTime = SystemClock.uptimeMillis();
}
if (app != null && app.thread != null) {
try {
//如果存在，则直接通知该应用进程将该Activity启动起来。
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.
}
//如果不存在，则用该Activity的用户ID和进程名称创建一个新的应用进程，再由该进程将该Activity启动起来。
mService.startProcessLocked(r.processName, r.info.applicationInfo, true, 0,
"activity", r.intent.getComponent(), false);
}
}在ActivityManagerService中，每个Activity组件都有一个用户ID和一个进程名称。
用户ID：安装该Activity时由PackageManagerService分配的。
进程名称：由Activity组件的android:process属性所决定的。ActivityManagerService在启动Activity时会用它的用户ID和进程名称来检查系统中是否存在一个对应的应用进程。
如果存在，则直接通知该应用进程将该Activity启动起来。
如果不存在，则用该Activity的用户ID和进程名称创建一个新的应用进程，再由该进程将该Activity启动起来。
我们这里的目标Activity是第一次启动，所以它会调用startProcessLocked()为目标Activity创建一个新的进程。
23 ActivityManagerService.startProcessLocked(String processName, ApplicationInfo info, boolean knownToBeDead, int intentFlags, String hostingType, ComponentName hostingName, boolean allowWhileBooting)
public final class ActivityManagerService extends ActivityManagerNative
implements Watchdog.Monitor, BatteryStatsImpl.BatteryCallback{
final ProcessRecord startProcessLocked(String processName,
ApplicationInfo info, boolean knownToBeDead, int intentFlags,
String hostingType, ComponentName hostingName, boolean allowWhileBooting) {
//检查请求创建的应用进程是否已经存在，如果已经存在，则不再创建。
ProcessRecord app = getProcessRecordLocked(processName, info.uid);
// We don't have to do anything more if:
// (1) There is an existing application record; and
// (2) The caller doesn't think it is dead, OR there is no thread
// object attached to it so we know it couldn't have crashed; and
// (3) There is a pid assigned to it, so it is either starting or
// already running.
if (DEBUG_PROCESSES) Slog.v(TAG, "startProcess: name=" + processName
+ " app=" + app + " knownToBeDead=" + knownToBeDead
+ " thread=" + (app != null ? app.thread : null)
+ " pid=" + (app != null ? app.pid : -1));
if (app != null && app.pid > 0) {
if (!knownToBeDead || app.thread == null) {
// We already have the app running, or are waiting for it to
// come up (we have a pid but not yet its thread), so keep it.
if (DEBUG_PROCESSES) Slog.v(TAG, "App already running: " + app);
return app;
} else {
// An application record is attached to a previous process,
// clean it up now.
if (DEBUG_PROCESSES) Slog.v(TAG, "App died: " + app);
handleAppDiedLocked(app, true);
}
}
String hostingNameStr = hostingName != null
? hostingName.flattenToShortString() : null;
if ((intentFlags&Intent.FLAG_FROM_BACKGROUND) != 0) {
// If we are in the background, then check to see if this process
// is bad. If so, we will just silently fail.
if (mBadProcesses.get(info.processName, info.uid) != null) {
if (DEBUG_PROCESSES) Slog.v(TAG, "Bad process: " + info.uid
+ "/" + info.processName);
return null;
}
} else {
// When the user is explicitly starting a process, then clear its
// crash count so that we won't make it bad until they see at
// least one crash dialog again, and make the process good again
// if it had been bad.
if (DEBUG_PROCESSES) Slog.v(TAG, "Clearing bad process: " + info.uid
+ "/" + info.processName);
mProcessCrashTimes.remove(info.processName, info.uid);
if (mBadProcesses.get(info.processName, info.uid) != null) {
EventLog.writeEvent(EventLogTags.AM_PROC_GOOD, info.uid,
info.processName);
mBadProcesses.remove(info.processName, info.uid);
if (app != null) {
app.bad = false;
}
}
}
if (app == null) {
app = newProcessRecordLocked(null, info, processName);
mProcessNames.put(processName, info.uid, app);
} else {
// If this is a new package in the process, add the package to the list
app.addPackage(info.packageName);
}
// If the system is not ready yet, then hold off on starting this
// process until it is.
if (!mProcessesReady
&& !isAllowedWhileBooting(info)
&& !allowWhileBooting) {
if (!mProcessesOnHold.contains(app)) {
mProcessesOnHold.add(app);
}
if (DEBUG_PROCESSES) Slog.v(TAG, "System not ready, putting on hold: " + app);
return app;
}
//如果不存在，则调用它的重载函数创建一个新的应用进程。
startProcessLocked(app, hostingType, hostingNameStr);
return (app.pid != 0) ? app : null;
}
}
该函数会检查请求创建的应用进程是否已经存在，如果已经存在，则不再创建。如果不存在，则调用它的重载函数startProcessLocked(app, hostingType, hostingNameStr)创建一个新的应用进程。
具体实现：
public final class ActivityManagerService extends ActivityManagerNative
implements Watchdog.Monitor, BatteryStatsImpl.BatteryCallback{
private final void startProcessLocked(ProcessRecord app,
String hostingType, String hostingNameStr) {
if (app.pid > 0 && app.pid != MY_PID) {
synchronized (mPidsSelfLocked) {
mPidsSelfLocked.remove(app.pid);
mHandler.removeMessages(PROC_START_TIMEOUT_MSG, app);
}
app.pid = 0;
}
if (DEBUG_PROCESSES && mProcessesOnHold.contains(app)) Slog.v(TAG,
"startProcessLocked removing on hold: " + app);
mProcessesOnHold.remove(app);
updateCpuStats();
System.arraycopy(mProcDeaths, 0, mProcDeaths, 1, mProcDeaths.length-1);
mProcDeaths[0] = 0;
try {
//获取将要创建的应用进程的用户ID与用户组ID。
int uid = app.info.uid;
int[] gids = null;
try {
gids = mContext.getPackageManager().getPackageGids(
app.info.packageName);
} catch (PackageManager.NameNotFoundException e) {
Slog.w(TAG, "Unable to retrieve gids", e);
}
if (mFactoryTest != SystemServer.FACTORY_TEST_OFF) {
if (mFactoryTest == SystemServer.FACTORY_TEST_LOW_LEVEL
&& mTopComponent != null
&& app.processName.equals(mTopComponent.getPackageName())) {
uid = 0;
}
if (mFactoryTest == SystemServer.FACTORY_TEST_HIGH_LEVEL
&& (app.info.flags&ApplicationInfo.FLAG_FACTORY_TEST) != 0) {
uid = 0;
}
}
int debugFlags = 0;
if ((app.info.flags & ApplicationInfo.FLAG_DEBUGGABLE) != 0) {
debugFlags |= Zygote.DEBUG_ENABLE_DEBUGGER;
}
// Run the app in safe mode if its manifest requests so or the
// system is booted in safe mode.
if ((app.info.flags & ApplicationInfo.FLAG_VM_SAFE_MODE) != 0 ||
Zygote.systemInSafeMode == true) {
debugFlags |= Zygote.DEBUG_ENABLE_SAFEMODE;
}
if ("1".equals(SystemProperties.get("debug.checkjni"))) {
debugFlags |= Zygote.DEBUG_ENABLE_CHECKJNI;
}
if ("1".equals(SystemProperties.get("debug.assert"))) {
debugFlags |= Zygote.DEBUG_ENABLE_ASSERT;
}
//创建一个新的应用进程。pid是一个大于0的ID
int pid = Process.start("android.app.ActivityThread",
mSimpleProcessManagement ? app.processName : null, uid, uid,
gids, debugFlags, null);
BatteryStatsImpl bs = app.batteryStats.getBatteryStats();
synchronized (bs) {
if (bs.isOnBattery()) {
app.batteryStats.incStartsLocked();
}
}
EventLog.writeEvent(EventLogTags.AM_PROC_START, pid, uid,
app.processName, hostingType,
hostingNameStr != null ? hostingNameStr : "");
if (app.persistent) {
Watchdog.getInstance().processStarted(app.processName, pid);
}
StringBuilder buf = mStringBuilder;
buf.setLength(0);
buf.append("Start proc ");
buf.append(app.processName);
buf.append(" for ");
buf.append(hostingType);
if (hostingNameStr != null) {
buf.append(" ");
buf.append(hostingNameStr);
}
buf.append(": pid=");
buf.append(pid);
buf.append(" uid=");
buf.append(uid);
buf.append(" gids={");
if (gids != null) {
for (int gi=0; giif (gi != 0) buf.append(", ");
buf.append(gids[gi]);
}
}
buf.append("}");
Slog.i(TAG, buf.toString());
if (pid == 0 || pid == MY_PID) {
// Processes are being emulated with threads.
app.pid = MY_PID;
app.removed = false;
mStartingProcesses.add(app);
} else if (pid > 0) {
app.pid = pid;
app.removed = false;
synchronized (mPidsSelfLocked) {
//以pid为关键字将app指向的一个ProcessRecord对象保存在mPidsSelfLocked中
this.mPidsSelfLocked.put(pid, app);
//向ActivityManagerService所在线程发送一个PROC_START_TIMEOUT_MSG消息，
Message msg = mHandler.obtainMessage(PROC_START_TIMEOUT_MSG);
msg.obj = app;
//该消息要求PROC_START_TIMEOUT时间内被处理，也就是说新的进必须在PROC_START_TIMEOUT
//时间内完成启动，并向ActivityManagerService发送一个启动通知，以便ActivityManagerService
//去启动Activity组件，否则ActivityManagerService则任务进程创建超时，则无法启动Activity。
mHandler.sendMessageDelayed(msg, PROC_START_TIMEOUT);
}
} else {
app.pid = 0;
RuntimeException e = new RuntimeException(
"Failure starting process " + app.processName
+ ": returned pid=" + pid);
Slog.e(TAG, e.getMessage(), e);
}
} catch (RuntimeException e) {
// XXX do better error recovery.
app.pid = 0;
Slog.e(TAG, "Failure starting process " + app.processName, e);
}
}
} 这个重载函数做了以下事情：
1 获取将要创建的应用进程的用户ID与用户组ID。
2 向ActivityManagerService所在线程发送一个PROC_START_TIMEOUT_MSG消息，该消息要求PROC_START_TIMEOUT时间内被处理，也就是说新的进必须在PROC_START_TIMEOUT,
时间内完成启动，并向ActivityManagerService发送一个启动通知，以便ActivityManagerService去启动Activity组件，否则ActivityManagerService则任务进程创建超时，则
无法启动Activity。上述函数调用Process.start()来启动一个新的应用进程，指定该进程的进入函数为android.app.ActivityThread的静态成员函数main.
int pid = Process.start("android.app.ActivityThread",
mSimpleProcessManagement ? app.processName : null, uid, uid,
gids, debugFlags, null);好了，我们接着看看进程是怎么创建的吧。
24 ActivityThread.main(String[] args)
public final class ActivityThread {
public static final void main(String[] args) {
SamplingProfilerIntegration.start();
Process.setArgV0("" );
//创建消息循环，并使当前进程进入该消息循环。
Looper.prepareMainLooper();
if (sMainThreadHandler == null) {
sMainThreadHandler = new Handler();
}
//创建ActivityThread对象
ActivityThread thread = new ActivityThread();
//向ActivityManagerService发送一个启动完成通知
thread.attach(false);
if (false) {
Looper.myLooper().setMessageLogging(new
LogPrinter(Log.DEBUG, "ActivityThread"));
}
Looper.loop();
if (Process.supportsProcesses()) {
throw new RuntimeException("Main thread loop unexpectedly exited");
}
thread.detach();
String name = (thread.mInitialApplication != null)
? thread.mInitialApplication.getPackageName()
: "" ;
Slog.i(TAG, "Main thread of " + name + " is now exiting");
}
}新的应用进程启动时主要做两件事情：
1 在进程中创建ActivityThread对象，创建ActivityThread对象时，会同时在其内部创建一个ApplicationThread对象，该对象是一个Binder本地对象，ActivityManagerService就是
通过它和应用进程通信的。
2 调用thread.attach(false)向ctivityManagerService发送启动完成通知。
3 调用Looper.prepareMainLooper()创建一个消息循环，并使当前进程进入到该消息循环中，
thread.attach(false)最终会去调用ActivityManagerProxy.attachApplication(IApplicationThread app)发送一个进程间通信请求。
25 ActivityManagerProxy.attachApplication(IApplicationThread app)
public final class ActivityManagerProxy{
public void attachApplication(IApplicationThread app) throws RemoteException{
Parcel data = Parcel.obtain();
Parcel reply = Parcel.obtain();
data.writeInterfaceToken(IActivityManager.descriptor);
data.writeStrongBinder(app.asBinder());
mRemote.transact(ATTACH_APPLICATION_TRANSACTION, data, reply, 0);
reply.readException();
data.recycle();
reply.recycle();
}
}将传递过来的参数包装成一个Parcel对象，并发起一个ATTACH_APPLICATION_TRANSACTION进程通信请求。
26 ActivityManagerService.attachApplication(IApplicationThread thread)
public final class ActivityManagerService extends ActivityManagerNative
implements Watchdog.Monitor, BatteryStatsImpl.BatteryCallback {
public final void attachApplication(IApplicationThread thread) {
synchronized (this) {
int callingPid = Binder.getCallingPid();
final long origId = Binder.clearCallingIdentity();
attachApplicationLocked(thread, callingPid);
Binder.restoreCallingIdentity(origId);
}
}
}attachApplication(IApplicationThread thread)接收到了新应用进程发送过来的ATTACH_APPLICATION_TRANSACTION进程通信请求之后，它就知道
新的应用进程已经创建，接着调用ActivityManagerService.attachApplicationLocked(IApplicationThread thread, int pid)继续执行Activity
的启动操作。
27 ActivityManagerService.attachApplicationLocked(IApplicationThread thread, int pid)
public final class ActivityManagerService extends ActivityManagerNative
implements Watchdog.Monitor, BatteryStatsImpl.BatteryCallback {
private final boolean attachApplicationLocked(IApplicationThread thread,
int pid) {
// Find the application record that is being attached... either via
// the pid if we are running in multiple processes, or just pull the
// next app record if we are emulating process with anonymous threads.
ProcessRecord app;
if (pid != MY_PID && pid >= 0) {
synchronized (mPidsSelfLocked) {
//通过新进程的pid取出对应的ProcessRecord对象，并保存在ProcessRecord app中。
app = mPidsSelfLocked.get(pid);
}
} else if (mStartingProcesses.size() > 0) {
app = mStartingProcesses.remove(0);
app.setPid(pid);
} else {
app = null;
}
if (app == null) {
Slog.w(TAG, "No pending application record for pid " + pid
+ " (IApplicationThread " + thread + "); dropping process");
EventLog.writeEvent(EventLogTags.AM_DROP_PROCESS, pid);
if (pid > 0 && pid != MY_PID) {
Process.killProcess(pid);
} else {
try {
thread.scheduleExit();
} catch (Exception e) {
// Ignore exceptions.
}
}
return false;
}
// If this application record is still attached to a previous
// process, clean it up now.
if (app.thread != null) {
handleAppDiedLocked(app, true);
}
// Tell the process all about itself.
if (localLOGV) Slog.v(
TAG, "Binding process pid " + pid + " to record " + app);
String processName = app.processName;
try {
thread.asBinder().linkToDeath(new AppDeathRecipient(
app, pid, thread), 0);
} catch (RemoteException e) {
app.resetPackageList();
startProcessLocked(app, "link fail", processName);
return false;
}
EventLog.writeEvent(EventLogTags.AM_PROC_BOUND, app.pid, app.processName);
app.thread = thread;
app.curAdj = app.setAdj = -100;
app.curSchedGroup = Process.THREAD_GROUP_DEFAULT;
app.setSchedGroup = Process.THREAD_GROUP_BG_NONINTERACTIVE;
app.forcingToForeground = null;
app.foregroundServices = false;
app.debugging = false;
//新进程已经在规定时间内创建，移除PROC_START_TIMEOUT_MSG消息
mHandler.removeMessages(PROC_START_TIMEOUT_MSG, app);
boolean normalMode = mProcessesReady || isAllowedWhileBooting(app.info);
List providers = normalMode ? generateApplicationProvidersLocked(app) : null;
if (!normalMode) {
Slog.i(TAG, "Launching preboot mode app: " + app);
}
if (localLOGV) Slog.v(
TAG, "New app record " + app
+ " thread=" + thread.asBinder() + " pid=" + pid);
try {
int testMode = IApplicationThread.DEBUG_OFF;
if (mDebugApp != null && mDebugApp.equals(processName)) {
testMode = mWaitForDebugger
? IApplicationThread.DEBUG_WAIT
: IApplicationThread.DEBUG_ON;
app.debugging = true;
if (mDebugTransient) {
mDebugApp = mOrigDebugApp;
mWaitForDebugger = mOrigWaitForDebugger;
}
}
// If the app is being launched for restore or full backup, set it up specially
boolean isRestrictedBackupMode = false;
if (mBackupTarget != null && mBackupAppName.equals(processName)) {
isRestrictedBackupMode = (mBackupTarget.backupMode == BackupRecord.RESTORE)
|| (mBackupTarget.backupMode == BackupRecord.BACKUP_FULL);
}
ensurePackageDexOpt(app.instrumentationInfo != null
? app.instrumentationInfo.packageName
: app.info.packageName);
if (app.instrumentationClass != null) {
ensurePackageDexOpt(app.instrumentationClass.getPackageName());
}
if (DEBUG_CONFIGURATION) Slog.v(TAG, "Binding proc "
+ processName + " with config " + mConfiguration);
thread.bindApplication(processName, app.instrumentationInfo != null
? app.instrumentationInfo : app.info, providers,
app.instrumentationClass, app.instrumentationProfileFile,
app.instrumentationArguments, app.instrumentationWatcher, testMode,
isRestrictedBackupMode || !normalMode,
mConfiguration, getCommonServicesLocked());
updateLruProcessLocked(app, false, true);
app.lastRequestedGc = app.lastLowMemory = SystemClock.uptimeMillis();
} catch (Exception e) {
// todo: Yikes! What should we do? For now we will try to
// start another process, but that could easily get us in
// an infinite loop of restarting processes...
Slog.w(TAG, "Exception thrown during bind!", e);
app.resetPackageList();
startProcessLocked(app, "bind fail", processName);
return false;
}
// Remove this record from the list of starting applications.
mPersistentStartingProcesses.remove(app);
if (DEBUG_PROCESSES && mProcessesOnHold.contains(app)) Slog.v(TAG,
"Attach application locked removing on hold: " + app);
mProcessesOnHold.remove(app);
boolean badApp = false;
boolean didSomething = false;
//查看栈顶Activity（也就是我们要启动的目标Activity）是否将要在当前进程中启动。
// See if the top visible activity is waiting to run in this process...
ActivityRecord hr = mMainStack.topRunningActivityLocked(null);
if (hr != null && normalMode) {
//检查目标Activity的用户ID与进程名称与app所描述的应用进程的用户ID与进程名称是否一致。
if (hr.app == null && app.info.uid == hr.info.applicationInfo.uid
&& processName.equals(hr.processName)) {
try {
//如果一致，则继续执行目标Activity启动操作。
if (mMainStack.realStartActivityLocked(hr, app, true, true)) {
didSomething = true;
}
} catch (Exception e) {
Slog.w(TAG, "Exception in new application when starting activity "
+ hr.intent.getComponent().flattenToShortString(), e);
badApp = true;
}
} else {
mMainStack.ensureActivitiesVisibleLocked(hr, null, processName, 0);
}
}
// Find any services that should be running in this process...
if (!badApp && mPendingServices.size() > 0) {
ServiceRecord sr = null;
try {
for (int i=0; iif (app.info.uid != sr.appInfo.uid
|| !processName.equals(sr.processName)) {
continue;
}
mPendingServices.remove(i);
i--;
realStartServiceLocked(sr, app);
didSomething = true;
}
} catch (Exception e) {
Slog.w(TAG, "Exception in new application when starting service "
+ sr.shortName, e);
badApp = true;
}
}
// Check if the next broadcast receiver is in this process...
BroadcastRecord br = mPendingBroadcast;
if (!badApp && br != null && br.curApp == app) {
try {
mPendingBroadcast = null;
processCurBroadcastLocked(br, app);
didSomething = true;
} catch (Exception e) {
Slog.w(TAG, "Exception in new application when starting receiver "
+ br.curComponent.flattenToShortString(), e);
badApp = true;
logBroadcastReceiverDiscardLocked(br);
finishReceiverLocked(br.receiver, br.resultCode, br.resultData,
br.resultExtras, br.resultAbort, true);
scheduleBroadcastsLocked();
// We need to reset the state if we fails to start the receiver.
br.state = BroadcastRecord.IDLE;
}
}
// Check whether the next backup agent is in this process...
if (!badApp && mBackupTarget != null && mBackupTarget.appInfo.uid == app.info.uid) {
if (DEBUG_BACKUP) Slog.v(TAG, "New app is backup target, launching agent for " + app);
ensurePackageDexOpt(mBackupTarget.appInfo.packageName);
try {
thread.scheduleCreateBackupAgent(mBackupTarget.appInfo, mBackupTarget.backupMode);
} catch (Exception e) {
Slog.w(TAG, "Exception scheduling backup agent creation: ");
e.printStackTrace();
}
}
if (badApp) {
// todo: Also need to kill application to deal with all
// kinds of exceptions.
handleAppDiedLocked(app, false);
return false;
}
if (!didSomething) {
updateOomAdjLocked();
}
return true;
}
} 该函数做了以下事情：
1 通过新进程的pid取出对应的ProcessRecord对象，并保存在ProcessRecord app中。
2 新进程已经在规定时间内创建，移除PROC_START_TIMEOUT_MSG消息.
3 查看栈顶Activity（也就是我们要启动的目标Activity）是否将要在当前进程中启动。这个主要检查目标Activity的用户ID与进程名称与app所描述的应用进程的用户ID与进程名称是否一致。
如果一致，则继续调用mMainStack.realStartActivityLocked(hr, app, true, true)，执行目标Activity启动操作。
28 ActivityStack.realStartActivityLocked(ActivityRecord r, ProcessRecord app, boolean andResume, boolean checkConfig)
public class ActivityStack{
final boolean realStartActivityLocked(ActivityRecord r,
ProcessRecord app, boolean andResume, boolean checkConfig)
throws RemoteException {
r.startFreezingScreenLocked(app, 0);
mService.mWindowManager.setAppVisibility(r, true);
// Have the window manager re-evaluate the orientation of
// the screen based on the new activity order. Note that
// as a result of this, it can call back into the activity
// manager with a new orientation. We don't care about that,
// because the activity is not currently running so we are
// just restarting it anyway.
if (checkConfig) {
Configuration config = mService.mWindowManager.updateOrientationFromAppTokens(
mService.mConfiguration,
r.mayFreezeScreenLocked(app) ? r : null);
mService.updateConfigurationLocked(config, r);
}
//表示它描述的Activity组件是在参数app描述的应用进程中启动。
r.app = app;
if (localLOGV) Slog.v(TAG, "Launching: " + r);
int idx = app.activities.indexOf(r);
if (idx < 0) {
//将目标Activity组件添加到该应用进程中。
app.activities.add(r);
}
mService.updateLruProcessLocked(app, true, true);
try {
if (app.thread == null) {
throw new RemoteException();
}
List results = null;
List newIntents = null;
if (andResume) {
results = r.results;
newIntents = r.newIntents;
}
if (DEBUG_SWITCH) Slog.v(TAG, "Launching: " + r
+ " icicle=" + r.icicle
+ " with results=" + results + " newIntents=" + newIntents
+ " andResume=" + andResume);
if (andResume) {
EventLog.writeEvent(EventLogTags.AM_RESTART_ACTIVITY,
System.identityHashCode(r),
r.task.taskId, r.shortComponentName);
}
if (r.isHomeActivity) {
mService.mHomeProcess = app;
}
mService.ensurePackageDexOpt(r.intent.getComponent().getPackageName());
//app.thread是一个类型为ApplicationTHreadProxy的Binder代理对象，向我们刚才新创建的应用进程发送一个
//进程间通信请求，通知前面创建的应用进程启动目标Activity组件，该Activity组件由ActivityRecord r来描述。
app.thread.scheduleLaunchActivity(new Intent(r.intent), r,
System.identityHashCode(r),
r.info, r.icicle, results, newIntents, !andResume,
mService.isNextTransitionForward());
if ((app.info.flags&ApplicationInfo.FLAG_CANT_SAVE_STATE) != 0) {
// This may be a heavy-weight process! Note that the package
// manager will ensure that only activity can run in the main
// process of the .apk, which is the only thing that will be
// considered heavy-weight.
if (app.processName.equals(app.info.packageName)) {
if (mService.mHeavyWeightProcess != null
&& mService.mHeavyWeightProcess != app) {
Log.w(TAG, "Starting new heavy weight process " + app
+ " when already running "
+ mService.mHeavyWeightProcess);
}
mService.mHeavyWeightProcess = app;
Message msg = mService.mHandler.obtainMessage(
ActivityManagerService.POST_HEAVY_NOTIFICATION_MSG);
msg.obj = r;
mService.mHandler.sendMessage(msg);
}
}
} catch (RemoteException e) {
if (r.launchFailed) {
// This is the second time we failed -- finish activity
// and give up.
Slog.e(TAG, "Second failure launching "
+ r.intent.getComponent().flattenToShortString()
+ ", giving up", e);
mService.appDiedLocked(app, app.pid, app.thread);
requestFinishActivityLocked(r, Activity.RESULT_CANCELED, null,
"2nd-crash");
return false;
}
// This is the first time we failed -- restart process and
// retry.
app.activities.remove(r);
throw e;
}
r.launchFailed = false;
if (updateLRUListLocked(r)) {
Slog.w(TAG, "Activity " + r
+ " being launched, but already in LRU list");
}
if (andResume) {
// As part of the process of launching, ActivityThread also performs
// a resume.
r.state = ActivityState.RESUMED;
r.icicle = null;
r.haveState = false;
r.stopped = false;
mResumedActivity = r;
r.task.touchActiveTime();
completeResumeLocked(r);
pauseIfSleepingLocked();
} else {
// This activity is not starting in the resumed state... which
// should look like we asked it to pause+stop (but remain visible),
// and it has done so and reported back the current icicle and
// other state.
r.state = ActivityState.STOPPED;
r.stopped = true;
}
// Launch the new version setup screen if needed. We do this -after-
// launching the initial activity (that is, home), so that it can have
// a chance to initialize itself while in the background, making the
// switch back to it faster and look better.
if (mMainStack) {
mService.startSetupActivityLocked();
}
return true;
}
} 该函数主要做了以下事情：
1 将目标Activity添加到新创建的进程的Activity组件列表中。
2 调用 app.thread.scheduleLaunchActivity()，向我们刚才新创建的应用进程发送一个进程间通信请求，通知前面创建的应用进程启动目标Activity组件。这里说一下这个app.thread，它是一个类型为ApplicationTHreadProxy的Binder代理对象。
29 ApplicationThreadProxy.scheduleLaunchActivity(Intent intent, IBinder token, int ident, ActivityInfo info, Bundle state, List pendingResults, List pendingNewIntents, boolean notResumed, boolean isForward)
class ApplicationThreadProxy implements IApplicationThread{
public final void scheduleLaunchActivity(Intent intent, IBinder token, int ident,
ActivityInfo info, Bundle state, List pendingResults,
List pendingNewIntents, boolean notResumed, boolean isForward)
throws RemoteException {
Parcel data = Parcel.obtain();
data.writeInterfaceToken(IApplicationThread.descriptor);
intent.writeToParcel(data, 0);
data.writeStrongBinder(token);
data.writeInt(ident);
info.writeToParcel(data, 0);
data.writeBundle(state);
data.writeTypedList(pendingResults);
data.writeTypedList(pendingNewIntents);
data.writeInt(notResumed ? 1 : 0);
data.writeInt(isForward ? 1 : 0);
mRemote.transact(SCHEDULE_LAUNCH_ACTIVITY_TRANSACTION, data, null,
IBinder.FLAG_ONEWAY);
data.recycle();
}
} 将传递过来的参数打包成一个Parcel对象，并发送一个类型为SCHEDULE_LAUNCH_ACTIVITY_TRANSACTION进程间通信请求。
30 ActivityThread.scheduleRelaunchActivity(IBinder token, List pendingResults, List pendingNewIntents, int configChanges, boolean notResumed, Configuration config)
public final class ActivityThread{
private final class ApplicationThread extends ApplicationThreadNative {
// we use token to identify this activity without having to send the
// activity itself back to the activity manager. (matters more with ipc)
public final void scheduleLaunchActivity(Intent intent, IBinder token, int ident,
ActivityInfo info, Bundle state, List pendingResults,
List pendingNewIntents, boolean notResumed, boolean isForward) {
ActivityClientRecord r = new ActivityClientRecord();
r.token = token;
r.ident = ident;
r.intent = intent;
r.activityInfo = info;
r.state = state;
r.pendingResults = pendingResults;
r.pendingIntents = pendingNewIntents;
r.startsNotResumed = notResumed;
r.isForward = isForward;
queueOrSendMessage(H.LAUNCH_ACTIVITY, r);
}
}
} ApplicationThread的scheduleRelaunchActivity()用来处理ActivityManagerService发出的SCHEDULE_LAUNCH_ACTIVITY_TRANSACTION进程通信请求。
它主要把将要启动的目标Activity的信息封装成一个ActivityClientRecord对象，再以ActivityClientRecord对象为参数，调用queueOrSendMessage()函数
，向新创建应用进程的主线程消息队列发送一个类型为LAUNCH_ACTIVITY的消息。
31 ActivityThread.queueOrSendMessage(int what, Object obj)
public final class ActivityThread{
// if the thread hasn't started yet, we don't have the handler, so just
// save the messages until we're ready.
private final void queueOrSendMessage(int what, Object obj) {
queueOrSendMessage(what, obj, 0, 0);
}
private final void queueOrSendMessage(int what, Object obj, int arg1) {
queueOrSendMessage(what, obj, arg1, 0);
}
private final void queueOrSendMessage(int what, Object obj, int arg1, int arg2) {
synchronized (this) {
if (DEBUG_MESSAGES) Slog.v(
TAG, "SCHEDULE " + what + " " + mH.codeToString(what)
+ ": " + arg1 + " / " + obj);
Message msg = Message.obtain();
msg.what = what;
msg.obj = obj;
msg.arg1 = arg1;
msg.arg2 = arg2;
mH.sendMessage(msg);
}
}
}将上一步传递过来的ActivityClientRecord对象封装成一个Message对象，并将消息LAUNCH_ACTIVITY发送。
32 H.handleMessage(Message msg)
public final class H extends Handler{
public void handleMessage(Message msg) {
if (DEBUG_MESSAGES) Slog.v(TAG, ">>> handling: " + msg.what);
switch (msg.what) {
case LAUNCH_ACTIVITY: {
//获取ActivityClientRecord对象
ActivityClientRecord r = (ActivityClientRecord)msg.obj;
//获取一个LoadedApk对象，并将它保存在ActivityClientRecord对象的成员变量packagInfo中。
r.packageInfo = getPackageInfoNoCheck(
r.activityInfo.applicationInfo);
handleLaunchActivity(r, null);
} break;
case RELAUNCH_ACTIVITY: {
ActivityClientRecord r = (ActivityClientRecord)msg.obj;
handleRelaunchActivity(r, msg.arg1);
} break;
case PAUSE_ACTIVITY:
handlePauseActivity((IBinder)msg.obj, false, msg.arg1 != 0, msg.arg2);
maybeSnapshot();
break;
case PAUSE_ACTIVITY_FINISHING:
handlePauseActivity((IBinder)msg.obj, true, msg.arg1 != 0, msg.arg2);
break;
case STOP_ACTIVITY_SHOW:
handleStopActivity((IBinder)msg.obj, true, msg.arg2);
break;
case STOP_ACTIVITY_HIDE:
handleStopActivity((IBinder)msg.obj, false, msg.arg2);
break;
case SHOW_WINDOW:
handleWindowVisibility((IBinder)msg.obj, true);
break;
case HIDE_WINDOW:
handleWindowVisibility((IBinder)msg.obj, false);
break;
case RESUME_ACTIVITY:
handleResumeActivity((IBinder)msg.obj, true,
msg.arg1 != 0);
break;
case SEND_RESULT:
handleSendResult((ResultData)msg.obj);
break;
case DESTROY_ACTIVITY:
handleDestroyActivity((IBinder)msg.obj, msg.arg1 != 0,
msg.arg2, false);
break;
case BIND_APPLICATION:
AppBindData data = (AppBindData)msg.obj;
handleBindApplication(data);
break;
case EXIT_APPLICATION:
if (mInitialApplication != null) {
mInitialApplication.onTerminate();
}
Looper.myLooper().quit();
break;
case NEW_INTENT:
handleNewIntent((NewIntentData)msg.obj);
break;
case RECEIVER:
handleReceiver((ReceiverData)msg.obj);
maybeSnapshot();
break;
case CREATE_SERVICE:
handleCreateService((CreateServiceData)msg.obj);
break;
case BIND_SERVICE:
handleBindService((BindServiceData)msg.obj);
break;
case UNBIND_SERVICE:
handleUnbindService((BindServiceData)msg.obj);
break;
case SERVICE_ARGS:
handleServiceArgs((ServiceArgsData)msg.obj);
break;
case STOP_SERVICE:
handleStopService((IBinder)msg.obj);
maybeSnapshot();
break;
case REQUEST_THUMBNAIL:
handleRequestThumbnail((IBinder)msg.obj);
break;
case CONFIGURATION_CHANGED:
handleConfigurationChanged((Configuration)msg.obj);
break;
case CLEAN_UP_CONTEXT:
ContextCleanupInfo cci = (ContextCleanupInfo)msg.obj;
cci.context.performFinalCleanup(cci.who, cci.what);
break;
case GC_WHEN_IDLE:
scheduleGcIdler();
break;
case DUMP_SERVICE:
handleDumpService((DumpServiceInfo)msg.obj);
break;
case LOW_MEMORY:
handleLowMemory();
break;
case ACTIVITY_CONFIGURATION_CHANGED:
handleActivityConfigurationChanged((IBinder)msg.obj);
break;
case PROFILER_CONTROL:
handleProfilerControl(msg.arg1 != 0, (ProfilerControlData)msg.obj);
break;
case CREATE_BACKUP_AGENT:
handleCreateBackupAgent((CreateBackupAgentData)msg.obj);
break;
case DESTROY_BACKUP_AGENT:
handleDestroyBackupAgent((CreateBackupAgentData)msg.obj);
break;
case SUICIDE:
Process.killProcess(Process.myPid());
break;
case REMOVE_PROVIDER:
completeRemoveProvider((IContentProvider)msg.obj);
break;
case ENABLE_JIT:
ensureJitEnabled();
break;
case DISPATCH_PACKAGE_BROADCAST:
handleDispatchPackageBroadcast(msg.arg1, (String[])msg.obj);
break;
case SCHEDULE_CRASH:
throw new RemoteServiceException((String)msg.obj);
}
if (DEBUG_MESSAGES) Slog.v(TAG, "<<< done: " + msg.what);
}
}上述方法做了两件事情：
1 获取ActivityClientRecord对象，获取一个LoadedApk对象，并将它保存在ActivityClientRecord对象的成员变量packagInfo中。
LoadedApk对象：每个Android应用都打包在一个APK文件中，APK文件包含应用的所有资源，LoadedApk对象就是用来描述一个已经被加载的APK文件。
2 调用handleLaunchActivity(r, null)方法来处理LAUNCH_ACTIVITY消息。
33 ActivityThread.handleLaunchActivity(ActivityClientRecord r, Intent customIntent)
public final class ActivityThread {
private final void handleLaunchActivity(ActivityClientRecord r, Intent customIntent) {
// If we are getting ready to gc after going to the background, well
// we are back active so skip it.
unscheduleGcIdler();
if (localLOGV) Slog.v(
TAG, "Handling launch of " + r);
//启动目标Activity组件
Activity a = performLaunchActivity(r, customIntent);
if (a != null) {
r.createdConfig = new Configuration(mConfiguration);
Bundle oldState = r.state;
//将目标Activity组件状态设置为Resumed状态，表示他是系统当前激活的Activity
handleResumeActivity(r.token, false, r.isForward);
if (!r.activity.mFinished && r.startsNotResumed) {
// The activity manager actually wants this one to start out
// paused, because it needs to be visible but isn't in the
// foreground. We accomplish this by going through the
// normal startup (because activities expect to go through
// onResume() the first time they run, before their window
// is displayed), and then pausing it. However, in this case
// we do -not- need to do the full pause cycle (of freezing
// and such) because the activity manager assumes it can just
// retain the current state it has.
try {
r.activity.mCalled = false;
mInstrumentation.callActivityOnPause(r.activity);
// We need to keep around the original state, in case
// we need to be created again.
r.state = oldState;
if (!r.activity.mCalled) {
throw new SuperNotCalledException(
"Activity " + r.intent.getComponent().toShortString() +
" did not call through to super.onPause()");
}
} catch (SuperNotCalledException e) {
throw e;
} catch (Exception e) {
if (!mInstrumentation.onException(r.activity, e)) {
throw new RuntimeException(
"Unable to pause activity "
+ r.intent.getComponent().toShortString()
+ ": " + e.toString(), e);
}
}
r.paused = true;
}
} else {
// If there was an error, for any reason, tell the activity
// manager to stop us.
try {
ActivityManagerNative.getDefault()
.finishActivity(r.token, Activity.RESULT_CANCELED, null);
} catch (RemoteException ex) {
}
}
}
}该函数主要做了两件事情：
1 调用performLaunchActivity(r, customIntent)启动目标Activity组件。
2 调用andleResumeActivity(r.token, false, r.isForward)将目标Activity组件状态设置为Resumed状态，表示他是系统当前激活的Activity34 ActivityThread.performLaunchActivity(ActivityClientRecord r, Intent customIntent)
public final class ActivityThread {
private final Activity performLaunchActivity(ActivityClientRecord r, Intent customIntent) {
// System.out.println("##### [" + System.currentTimeMillis() + "] ActivityThread.performLaunchActivity(" + r + ")");
ActivityInfo aInfo = r.activityInfo;
if (r.packageInfo == null) {
r.packageInfo = getPackageInfo(aInfo.applicationInfo,
Context.CONTEXT_INCLUDE_CODE);
}
//获取Activity组件的包名以及类名
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);
}
//将目标Activity类文件加载到内存中，并且创建一个实例。
Activity activity = null;
try {
java.lang.ClassLoader cl = r.packageInfo.getClassLoader();
activity = mInstrumentation.newActivity(
cl, component.getClassName(), r.intent);
r.intent.setExtrasClassLoader(cl);
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());
if (activity != null) {
//创建一个ContextImpl对象，它将作为Activity运行的上下文环境，通过它就可以访问特定的应用程序资源
//，以及启动应用程序组件。
ContextImpl appContext = new ContextImpl();
appContext.init(r.packageInfo, r.token, this);
appContext.setOuterContext(activity);
CharSequence title = r.activityInfo.loadLabel(appContext.getPackageManager());
Configuration config = new Configuration(mConfiguration);
if (DEBUG_CONFIGURATION) Slog.v(TAG, "Launching activity "
+ r.activityInfo.name + " with config " + config);
//使用ContextImpl对象和ActivityClientRecord对象来初始化Activity组件
activity.attach(appContext, this, getInstrumentation(), r.token,
r.ident, app, r.intent, r.activityInfo, title, r.parent,
r.embeddedID, r.lastNonConfigurationInstance,
r.lastNonConfigurationChildInstances, config);
if (customIntent != null) {
activity.mIntent = customIntent;
}
r.lastNonConfigurationInstance = null;
r.lastNonConfigurationChildInstances = null;
activity.mStartedActivity = false;
int theme = r.activityInfo.getThemeResource();
if (theme != 0) {
activity.setTheme(theme);
}
activity.mCalled = false;
//Activity初始化完成后，调用mInstrumentation.callActivityOnCreate(activity, r.state)将Activity启动起来
mInstrumentation.callActivityOnCreate(activity, r.state);
if (!activity.mCalled) {
throw new SuperNotCalledException(
"Activity " + r.intent.getComponent().toShortString() +
" did not call through to super.onCreate()");
}
r.activity = activity;
r.stopped = true;
if (!r.activity.mFinished) {
activity.performStart();
r.stopped = false;
}
if (!r.activity.mFinished) {
if (r.state != null) {
mInstrumentation.callActivityOnRestoreInstanceState(activity, r.state);
}
}
if (!r.activity.mFinished) {
activity.mCalled = false;
mInstrumentation.callActivityOnPostCreate(activity, r.state);
if (!activity.mCalled) {
throw new SuperNotCalledException(
"Activity " + r.intent.getComponent().toShortString() +
" did not call through to super.onPostCreate()");
}
}
}
r.paused = true;
mActivities.put(r.token, r);
} 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;
}
}
这个函数正式开始Activity组件的初始化以及启动工作，我们来具体看看。
1 获取Activity组件的包名以及类名
2 将目标Activity类文件加载到内存中，并且创建一个实例。
3 创建一个ContextImpl对象，它将作为Activity运行的上下文环境，通过它就可以访问特定的应用程序资源，以及启动应用程序组件。使用ContextImpl对象和ActivityClientRecord对象
来初始化Activity组件。
4 Activity初始化完成后，调用mInstrumentation.callActivityOnCreate(activity, r.state)将Activity启动起来，我们来看看该函数的具体实现：
public class Instrumentation {
/**
* Perform calling of an activity's {Activity#onCreate}
* method. The default implementation simply calls through to that method.
*
* @param activity The activity being created.
* @param icicle The previously frozen state (or null) to pass through to
* onCreate().
*/
public void callActivityOnCreate(Activity activity, Bundle icicle) {
if (mWaitingActivities != null) {
synchronized (mSync) {
final int N = mWaitingActivities.size();
for (int i=0; ifinal ActivityWaiter aw = mWaitingActivities.get(i);
final Intent intent = aw.intent;
if (intent.filterEquals(activity.getIntent())) {
aw.activity = activity;
mMessageQueue.addIdleHandler(new ActivityGoing(aw));
}
}
}
}
activity.onCreate(icicle);
if (mActivityMonitors != null) {
synchronized (mSync) {
final int N = mActivityMonitors.size();
for (int i=0; ifinal ActivityMonitor am = mActivityMonitors.get(i);
am.match(activity, activity, activity.getIntent());
}
}
}
}
} 可以看到该函数最终调用了Activity的onCreate()方法。
35 Activity.onCreate(Bundle savedInstanceState)
public class Activity extends ContextThemeWrapper
implements LayoutInflater.Factory,
Window.Callback, KeyEvent.Callback,
OnCreateContextMenuListener, ComponentCallbacks {
/**
* Called when the activity is starting. This is where most initialization
* should go: calling { #setContentView(int)} to inflate the
* activity's UI, using { #findViewById} to programmatically interact
* with widgets in the UI, calling
* { #managedQuery(android.net.Uri , String[], String, String[], String)} to retrieve
* cursors for data being displayed, etc.
*
* You can call { #finish} from within this function, in
* which case onDestroy() will be immediately called without any of the rest
* of the activity lifecycle ({ #onStart}, { #onResume},
* { #onPause}, etc) executing.
*
*
Derived classes must call through to the super class's
* implementation of this method. If they do not, an exception will be
* thrown.
*
* @param savedInstanceState If the activity is being re-initialized after
* previously being shut down then this Bundle contains the data it most
* recently supplied in {onSaveInstanceState}. Note: Otherwise it is null.
*/
protected void onCreate(Bundle savedInstanceState) {
mVisibleFromClient = !mWindow.getWindowStyle().getBoolean(
com.android.internal.R.styleable.Window_windowNoDisplay, false);
mCalled = true;
}
/**
* Finds a view that was identified by the id attribute from the XML that
* was processed in {@link #onCreate}.
*
* @return The view if found or null otherwise.
*/
public View findViewById(int id) {
return getWindow().findViewById(id);
}
/**
* Set the activity content from a layout resource. The resource will be
* inflated, adding all top-level views to the activity.
*
* @param layoutResID Resource ID to be inflated.
*/
public void setContentView(int layoutResID) {
getWindow().setContentView(layoutResID);
}
/**
* Set the activity content to an explicit view. This view is placed
* directly into the activity's view hierarchy. It can itself be a complex
* view hierarhcy.
*
* @param view The desired content to display.
*/
public void setContentView(View view) {
getWindow().setContentView(view);
}
/**
* Set the activity content to an explicit view. This view is placed
* directly into the activity's view hierarchy. It can itself be a complex
* view hierarhcy.
*
* @param view The desired content to display.
* @param params Layout parameters for the view.
*/
public void setContentView(View view, ViewGroup.LayoutParams params) {
getWindow().setContentView(view, params);
}
/**
* Add an additional content view to the activity. Added after any existing
* ones in the activity -- existing views are NOT removed.
*
* @param view The desired content to display.
* @param params Layout parameters for the view.
*/
public void addContentView(View view, ViewGroup.LayoutParams params) {
getWindow().addContentView(view, params);
}
}全面人民万众瞩目，翘首以盼的onCreate()函数终于来到了我们面前。
我们平时常见的Activity代码：
public class MainActivity extends AppCompatActivity implements View.OnClickListener {
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
findViewById(R.id.btn_application).setOnClickListener(this);
findViewById(R.id.btn_system).setOnClickListener(this);
findViewById(R.id.btn_program).setOnClickListener(this);
}
@Override
public void onClick(View view) {
switch (view.getId()) {
case R.id.btn_application: {
Intent intent = new Intent(MainActivity.this, ApplicationActivity.class);
startActivity(intent);
}
break;
case R.id.btn_system: {
Intent intent = new Intent(MainActivity.this, SystemActivity.class);
startActivity(intent);
}
break;
case R.id.btn_program: {
Intent intent = new Intent(MainActivity.this, ProgramActivity.class);
startActivity(intent);
}
break;
}
}
}
onCreate()主要用来加载用户界面，以及对用户界面上的组件进行初始化，