深入理解AMS --- 二 Activity 的啟動

摘要： 深入理解AMS --- 二 Activity 的啟動 以桌面啟動應用為例分析一下啟動一個新的應用的Activiy的過程。 啟動Activity 1.1 Activity#startActivity 在launchu 程序中呼叫 Activity.startActivity 啟動...

深入理解AMS --- 二 Activity 的啟動

以桌面啟動應用為例分析一下啟動一個新的應用的Activiy的過程。

啟動Activity

1.1 Activity#startActivity

在launchu 程序中呼叫 Activity.startActivity 啟動一個新的Activity.

最後呼叫到Instrumentation#execStartActivity

Activity.java:

public void startActivity(Intent intent) {
this.startActivity(intent, null);
}

public void startActivity(Intent intent) {
this.startActivity(intent, null);
} 

public void startActivityForResult(@RequiresPermission Intent intent, int requestCode,
@Nullable Bundle options) {
if (mParent == null) {
options = transferSpringboardActivityOptions(options);
Instrumentation.ActivityResult ar =
mInstrumentation.execStartActivity(
this, mMainThread.getApplicationThread(), mToken, this,
intent, requestCode, options);
} else {

}
}

1.2 Instrumentation#execStartActivity

在Instrumentation#execStartActivity 中獲取AMS的代理，然後呼叫AMS的startActivity

Instrumentation.java:

 public ActivityResult execStartActivity(
Context who, IBinder contextThread, IBinder token, Activity target,
Intent intent, int requestCode, Bundle options) {

try {
int result = ActivityManager.getService()
.startActivity(whoThread, who.getBasePackageName(), 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);
}
return null;
}

AMS 程序中startActivity

2.1 AMS startActivity 的堆疊

at android.app.IApplicationThread$Stub$Proxy.scheduleTransaction(IApplicationThread.java:1767)
at android.app.servertransaction.ClientTransaction.schedule(ClientTransaction.java:129)
at com.android.server.am.ClientLifecycleManager.scheduleTransaction(ClientLifecycleManager.java:47)
at com.android.server.am.ClientLifecycleManager.scheduleTransaction(ClientLifecycleManager.java:69)
at com.android.server.am.ActivityStack.startPausingLocked(ActivityStack.java:1463)
at com.android.server.am.ActivityStack.resumeTopActivityInnerLocked(ActivityStack.java:2445)
at com.android.server.am.ActivityStack.resumeTopActivityUncheckedLocked(ActivityStack.java:2292)
at com.android.server.am.ActivityStackSupervisor.resumeFocusedStackTopActivityLocked(ActivityStackSupervisor.java:2222)
at com.android.server.am.ActivityStarter.startActivityUnchecked(ActivityStarter.java:1466)
at com.android.server.am.ActivityStarter.startActivity(ActivityStarter.java:1200)
at com.android.server.am.ActivityStarter.startActivity(ActivityStarter.java:868)
at com.android.server.am.ActivityStarter.startActivity(ActivityStarter.java:544)
at com.android.server.am.ActivityStarter.startActivityMayWait(ActivityStarter.java:1099)
- locked <0x3741> (a com.android.server.am.ActivityManagerService)
at com.android.server.am.ActivityStarter.execute(ActivityStarter.java:486)
at com.android.server.am.ActivityManagerService.startActivityAsUser(ActivityManagerService.java:5117)
at com.android.server.am.ActivityManagerService.startActivityAsUser(ActivityManagerService.java:5091)
at com.android.server.am.ActivityManagerService.startActivity(ActivityManagerService.java:5082)
at android.app.IActivityManager$Stub.onTransact$startActivity$(IActivityManager.java:10084)
at android.app.IActivityManager$Stub.onTransact(IActivityManager.java:122)
at com.android.server.am.ActivityManagerService.onTransact(ActivityManagerService.java:3288)
at android.os.Binder.execTransact(Binder.java:731)

2.2 ActivityStarter#startActivity

ActivityStarter#startActivityMayWait 中new 一個ActivityRecord， ActivityRecord 為Activity 在AMS中的表示，然後在下面的startActivity中賦值。並且找到Activity 所在的ActivityStack.

startActivityUnchecked 中呼叫ActivityStack#startActivityLocked 找到Activity 所在的TaskRecord, 把Activity 插入TaskRecord 合適的位置。呼叫

ActivityStackSupervisor#resumeFocusedStackTopActivityLocked

ActivityStarter.java 

@Override
public final int startActivity(IApplicationThread caller, String callingPackage,
Intent intent, String resolvedType, IBinder resultTo, String resultWho, int requestCode,
int startFlags, ProfilerInfo profilerInfo, Bundle bOptions) {
return startActivityAsUser(caller, callingPackage, intent, resolvedType, resultTo,
resultWho, requestCode, startFlags, profilerInfo, bOptions,
UserHandle.getCallingUserId());
}


private int startActivityMayWait(IApplicationThread caller, int callingUid,
String callingPackage, Intent intent, String resolvedType,
IVoiceInteractionSession voiceSession, IVoiceInteractor voiceInteractor,
IBinder resultTo, String resultWho, int requestCode, int startFlags,
ProfilerInfo profilerInfo, WaitResult outResult,
Configuration globalConfig, SafeActivityOptions options, boolean ignoreTargetSecurity,
int userId, TaskRecord inTask, String reason,
boolean allowPendingRemoteAnimationRegistryLookup) {

synchronized (mService) {
final ActivityStack stack = mSupervisor.mFocusedStack;

final ActivityRecord[] outRecord = new ActivityRecord[1];
int res = startActivity(caller, intent, ephemeralIntent, resolvedType, aInfo, rInfo,
voiceSession, voiceInteractor, resultTo, resultWho, requestCode, callingPid,
callingUid, callingPackage, realCallingPid, realCallingUid, startFlags, options,
ignoreTargetSecurity, componentSpecified, outRecord, inTask, reason,
allowPendingRemoteAnimationRegistryLookup);
}

private int startActivity(IApplicationThread caller, Intent intent, Intent ephemeralIntent,
String resolvedType, ActivityInfo aInfo, ResolveInfo rInfo,
IVoiceInteractionSession voiceSession, IVoiceInteractor voiceInteractor,
IBinder resultTo, String resultWho, int requestCode, int callingPid, int callingUid,
String callingPackage, int realCallingPid, int realCallingUid, int startFlags,
SafeActivityOptions options,
boolean ignoreTargetSecurity, boolean componentSpecified, ActivityRecord[] outActivity,
TaskRecord inTask, boolean allowPendingRemoteAnimationRegistryLookup) {

ActivityRecord r = new ActivityRecord(mService, callerApp, callingPid, callingUid,
callingPackage, intent, resolvedType, aInfo, mService.getGlobalConfiguration(),
resultRecord, resultWho, requestCode, componentSpecified, voiceSession != null,
mSupervisor, checkedOptions, sourceRecord);
if (outActivity != null) {
outActivity[0] = r;
}

final ActivityStack stack = mSupervisor.mFocusedStack;

return startActivity(r, sourceRecord, voiceSession, voiceInteractor, startFlags,
true /* doResume */, checkedOptions, inTask, outActivity);
}


private int startActivityUnchecked(final ActivityRecord r, ActivityRecord sourceRecord,
IVoiceInteractionSession voiceSession, IVoiceInteractor voiceInteractor,
int startFlags, boolean doResume, ActivityOptions options, TaskRecord inTask,
ActivityRecord[] outActivity) {


mTargetStack.startActivityLocked(mStartActivity, topFocused, newTask, mKeepCurTransition,
mOptions);

if (mDoResume) {
if (!mTargetStack.isFocusable()
|| (topTaskActivity != null && topTaskActivity.mTaskOverlay
&& mStartActivity != topTaskActivity)) {

} else {
mSupervisor.resumeFocusedStackTopActivityLocked(mTargetStack, mStartActivity,
mOptions);
}
} else if (mStartActivity != null) {
}
return START_SUCCESS;
}

2.3 ActivityStackSupervisor#resumeFocusedStackTopActivityLocked

Activity 已經在進入ActivityStack， 然後從Activity 中查詢這個Activity 然後調狀態設定為resume.

ActivityStackSupervisor.java

boolean resumeFocusedStackTopActivityLocked(
ActivityStack targetStack, ActivityRecord target, ActivityOptions targetOptions) {

if (!readyToResume()) {
return false;
}

if (targetStack != null && isFocusedStack(targetStack)) {
return targetStack.resumeTopActivityUncheckedLocked(target, targetOptions);
}

return false;
}

繼續回到 ActivityStack resume Activity.在resumeTopActivityInnerLocked 中先檢查桌面的

Activity 狀態，桌面Activity 狀態需要設定為pause, startPausingLocked 把桌面Activity設定為paused。 由於新的Activity 在另外一個程序中，另外一個程序還沒有啟動，mStackSupervisor.startSpecificActivityLocked 啟動新的Activity 程序。

ActivityStack.java

boolean resumeTopActivityUncheckedLocked(ActivityRecord prev, ActivityOptions options) {
if (mStackSupervisor.inResumeTopActivity) {
// Don't even start recursing.
return false;
}

boolean result = false;
try {
// Protect against recursion.
mStackSupervisor.inResumeTopActivity = true;
result = resumeTopActivityInnerLocked(prev, options);

// When resuming the top activity, it may be necessary to pause the top activity (for
// example, returning to the lock screen. We suppress the normal pause logic in
// {@link #resumeTopActivityUncheckedLocked}, since the top activity is resumed at the
// end. We call the {@link ActivityStackSupervisor#checkReadyForSleepLocked} again here
// to ensure any necessary pause logic occurs. In the case where the Activity will be
// shown regardless of the lock screen, the call to
// {@link ActivityStackSupervisor#checkReadyForSleepLocked} is skipped.
final ActivityRecord next = topRunningActivityLocked(true /* focusableOnly */);
if (next == null || !next.canTurnScreenOn()) {
checkReadyForSleep();
}
} finally {
mStackSupervisor.inResumeTopActivity = false;
}

return result;
}

private boolean resumeTopActivityInnerLocked(ActivityRecord prev, ActivityOptions options) {

boolean pausing = mStackSupervisor.pauseBackStacks(userLeaving, next, false);
if (mResumedActivity != null) {
if (DEBUG_STATES) Slog.d(TAG_STATES,
"resumeTopActivityLocked: Pausing " + mResumedActivity);
pausing |= startPausingLocked(userLeaving, false, next, false);
}

if (next.app != null && next.app.thread != null) {

} else {
mStackSupervisor.startSpecificActivityLocked(next, true, true);
}

return true;
}

final boolean startPausingLocked(boolean userLeaving, boolean uiSleeping,
ActivityRecord resuming, boolean pauseImmediately) {

if (prev.app != null && prev.app.thread != null) {
mService.getLifecycleManager().scheduleTransaction(prev.app.thread, prev.appToken,
PauseActivityItem.obtain(prev.finishing, userLeaving,
prev.configChangeFlags, pauseImmediately));
} catch (Exception e) {

}
} else {

}
}

3 桌面Activity pause

at android.app.IApplicationThread$Stub$Proxy.scheduleTransaction(IApplicationThread.java:1767)
at android.app.servertransaction.ClientTransaction.schedule(ClientTransaction.java:129)
at com.android.server.am.ClientLifecycleManager.scheduleTransaction(ClientLifecycleManager.java:47)
at com.android.server.am.ClientLifecycleManager.scheduleTransaction(ClientLifecycleManager.java:69)
at com.android.server.am.ActivityStack.startPausingLocked(ActivityStack.java:1463)

3.1 ApplicationThread#scheduleTransaction

通過 ActivityStack.startPausingLocked 函式paused 桌面Activity.通過呼叫棧可以看出呼叫了IApplicationThread#scheduleTransaction 通知桌面程序。 ApplicationThread 相關的類也是binder 呼叫。 ApplicationThread 的Stub 在桌面程序，是ActivityThread 的一個內部類。

private class ApplicationThread extends IApplicationThread.Stub

scheduleTransaction 函式把相關的訊息通知到ActivityThread 的

class H extends Handler

3.2 H#handleMessage

然後進入了桌面程序的主執行緒中進行訊息迴圈，在 H#handleMessage 處理訊息。

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;

3.3 TransactionExecutor#execute

在TransactionExecutor 中呼叫了函式executeCallbacks。executeCallbacks中還原出PauseActivityItem。

TransactionExecutor.java

public void execute(ClientTransaction transaction) {
final IBinder token = transaction.getActivityToken();
log("Start resolving transaction for client: " + mTransactionHandler + ", token: " + token);

executeCallbacks(transaction);

executeLifecycleState(transaction);
mPendingActions.clear();
log("End resolving transaction");
}

public void executeCallbacks(ClientTransaction transaction) {
final List<ClientTransactionItem> callbacks = transaction.getCallbacks();

final IBinder token = transaction.getActivityToken();
ActivityClientRecord r = mTransactionHandler.getActivityClient(token);

final int size = callbacks.size();
for (int i = 0; i < size; ++i) {
final ClientTransactionItem item = callbacks.get(i);
log("Resolving callback: " + item);


item.execute(mTransactionHandler, token, mPendingActions);
item.postExecute(mTransactionHandler, token, mPendingActions);
}
}

3.4 PauseActivityItem

1. PauseActivityItem 的execute 執行ActivityThread 的handlePauseActivity。
   然後呼叫Activity的 performPaused， 桌面的Activity 進入暫停狀態
2. postExecute 呼叫AMS activityPaused，通知AMS 桌面Activity pause.

PauseActivityItem.java


public class PauseActivityItem extends ActivityLifecycleItem {

private static final String TAG = "PauseActivityItem";

private boolean mFinished;
private boolean mUserLeaving;
private int mConfigChanges;
private boolean mDontReport;

@Override
public void execute(ClientTransactionHandler client, IBinder token,
PendingTransactionActions pendingActions) {
Trace.traceBegin(TRACE_TAG_ACTIVITY_MANAGER, "activityPause");
client.handlePauseActivity(token, mFinished, mUserLeaving, mConfigChanges, pendingActions,
"PAUSE_ACTIVITY_ITEM");
Trace.traceEnd(TRACE_TAG_ACTIVITY_MANAGER);
}

@Override
public void postExecute(ClientTransactionHandler client, IBinder token,
PendingTransactionActions pendingActions) {
if (mDontReport) {
return;
}
try {
// TODO(lifecycler): Use interface callback instead of AMS.
ActivityManager.getService().activityPaused(token);
} catch (RemoteException ex) {
throw ex.rethrowFromSystemServer();
}
}

AMS

@Override
public final void activityPaused(IBinder token) {
final long origId = Binder.clearCallingIdentity();
synchronized(this) {
ActivityStack stack = ActivityRecord.getStackLocked(token);
if (stack != null) {
stack.activityPausedLocked(token, false);
}
}
Binder.restoreCallingIdentity(origId);
}

四 AMS 啟動新程序

AMS pause 桌面Activity, 開始啟動新Activity 所在的程序

4.1 startProcessLocked

startSpecificActivityLocked 檢查Activity所在的程序是否真的啟動。Activity 所在的程序還沒有啟動，啟動Activity 所在的程序。

ActivityStackSupervisor.java 

void startSpecificActivityLocked(ActivityRecord r,
boolean andResume, boolean checkConfig) {
ProcessRecord app = mService.getProcessRecordLocked(r.processName,
r.info.applicationInfo.uid, true);

if (app != null && app.thread != null) {

realStartActivityLocked(r, app, andResume, checkConfig);
return;
} catch (RemoteException e) {

}

}

mService.startProcessLocked(r.processName, r.info.applicationInfo, true, 0,
"activity", r.intent.getComponent(), false, false, true);
}

startProcessLocked 要檢查多App 共享程序的情況。

AMS

final ProcessRecord startProcessLocked(String processName, ApplicationInfo info,
boolean knownToBeDead, int intentFlags, String hostingType, ComponentName hostingName,
boolean allowWhileBooting, boolean isolated, int isolatedUid, boolean keepIfLarge,
String abiOverride, String entryPoint, String[] entryPointArgs, Runnable crashHandler) {


final boolean success = startProcessLocked(app, hostingType, 
}

private ProcessStartResult startProcess(String hostingType, String entryPoint,
ProcessRecord app, int uid, int[] gids, int runtimeFlags, int mountExternal,
String seInfo, String requiredAbi, String instructionSet, String invokeWith,
long startTime) {
try {
Trace.traceBegin(Trace.TRACE_TAG_ACTIVITY_MANAGER, "Start proc: " +
app.processName);
checkTime(startTime, "startProcess: asking zygote to start proc");
final ProcessStartResult startResult;
if (hostingType.equals("webview_shttp://assets.processon.com/chart_image/5bda76eee4b0878bf41d8334.png?_=1543231861493ervice")) {
startResult = startWebView(entryPoint,
app.processName, uid, uid, gids, runtimeFlags, mountExternal,
app.info.targetSdkVersion, seInfo, requiredAbi, instructionSet,
app.info.dataDir, null,
new String[] {PROC_START_SEQ_IDENT + app.startSeq});
} else {
startResult = Process.start(entryPoint,
app.processName, uid, uid, gids, runtimeFlags, mountExternal,
app.info.targetSdkVersion, seInfo, requiredAbi, instructionSet,
app.info.dataDir, invokeWith,
new String[] {PROC_START_SEQ_IDENT + app.startSeq});
}
checkTime(startTime, "startProcess: returned from zygote!");
return startResult;
} finally {
Trace.traceEnd(Trace.TRACE_TAG_ACTIVITY_MANAGER);
}
}

public static final ProcessStartResult start(final String processClass,
final String niceName,
int uid, int gid, int[] gids,
int runtimeFlags, int mountExternal,
int targetSdkVersion,
String seInfo,
String abi,
String instructionSet,
String appDataDir,
String invokeWith,
String[] zygoteArgs) {
return zygoteProcess.start(processClass, niceName, uid, gid, gids,
runtimeFlags, mountExternal, targetSdkVersion, seInfo,
abi, instructionSet, appDataDir, invokeWith, zygoteArgs);
}

public final Process.ProcessStartResult start(final String processClass,
final String niceName,
int uid, int gid, int[] gids,
int runtimeFlags, int mountExternal,
int targetSdkVersion,
String seInfo,
String abi,
String instructionSet,
String appDataDir,
String invokeWith,
String[] zygoteArgs) {
try {
return startViaZygote(processClass, niceName, uid, gid, gids,
runtimeFlags, mountExternal, targetSdkVersion, seInfo,
abi, instructionSet, appDataDir, invokeWith, false /* startChildZygote */,
zygoteArgs);
} catch (ZygoteStartFailedEx ex) {
Log.e(LOG_TAG,
"Starting VM process through Zygote failed");
throw new RuntimeException(
"Starting VM process through Zygote failed", ex);
}
}

private Process.ProcessStartResult startViaZygote(final String processClass,
final String niceName,
final int uid, final int gid,
final int[] gids,
int runtimeFlags, int mountExternal,
int targetSdkVersion,
String seInfo,
String abi,
String instructionSet,
String appDataDir,
String invokeWith,
boolean startChildZygote,
String[] extraArgs)
throws ZygoteStartFailedEx {
ArrayList<String> argsForZygote = new ArrayList<String>();

// --runtime-args, --setuid=, --setgid=,
// and --setgroups= must go first
argsForZygote.add("--runtime-args");
argsForZygote.add("--setuid=" + uid);
argsForZygote.add("--setgid=" + gid);
argsForZygote.add("--runtime-flags=" + runtimeFlags);
if (mountExternal == Zygote.MOUNT_EXTERNAL_DEFAULT) {
argsForZygote.add("--mount-external-default");
} else if (mountExternal == Zygote.MOUNT_EXTERNAL_READ) {
argsForZygote.add("--mount-external-read");
} else if (mountExternal == Zygote.MOUNT_EXTERNAL_WRITE) {
argsForZygote.add("--mount-external-write");
}
argsForZygote.add("--target-sdk-version=" + targetSdkVersion);

// --setgroups is a comma-separated list
if (gids != null && gids.length > 0) {
StringBuilder sb = new StringBuilder();
sb.append("--setgroups=");

int sz = gids.length;
for (int i = 0; i < sz; i++) {
if (i != 0) {
sb.append(',');
}
sb.append(gids[i]);
}

argsForZygote.add(sb.toString());
}

if (niceName != null) {
argsForZygote.add("--nice-name=" + niceName);
}

if (seInfo != null) {
argsForZygote.add("--seinfo=" + seInfo);
}

if (instructionSet != null) {
argsForZygote.add("--instruction-set=" + instructionSet);
}

if (appDataDir != null) {
argsForZygote.add("--app-data-dir=" + appDataDir);
}

if (invokeWith != null) {
argsForZygote.add("--invoke-with");
argsForZygote.add(invokeWith);
}

if (startChildZygote) {
argsForZygote.add("--start-child-zygote");
}

argsForZygote.add(processClass);

if (extraArgs != null) {
for (String arg : extraArgs) {
argsForZygote.add(arg);
}
}

synchronized(mLock) {
return zygoteSendArgsAndGetResult(openZygoteSocketIfNeeded(abi), argsForZygote);
}
}

// 通過socket 檢查新程序的啟動情況
 private static Process.ProcessStartResult zygoteSendArgsAndGetResult(
ZygoteState zygoteState, ArrayList<String> args)
throws ZygoteStartFailedEx {
try {


/**
* See com.android.internal.os.SystemZygoteInit.readArgumentList()
* Presently the wire format to the zygote process is:
* a) a count of arguments (argc, in essence)
* b) a number of newline-separated argument strings equal to count
*
* After the zygote process reads these it will write the pid of
* the child or -1 on failure, followed by boolean to
* indicate whether a wrapper process was used.
*/
final BufferedWriter writer = zygoteState.writer;
final DataInputStream inputStream = zygoteState.inputStream;

writer.write(Integer.toString(args.size()));
writer.newLine();

for (int i = 0; i < sz; i++) {
String arg = args.get(i);
writer.write(arg);
writer.newLine();
}

writer.flush();

// Should there be a timeout on this?
Process.ProcessStartResult result = new Process.ProcessStartResult();

// Always read the entire result from the input stream to avoid leaving
// bytes in the stream for future process starts to accidentally stumble
// upon.
result.pid = inputStream.readInt();
result.usingWrapper = inputStream.readBoolean();

if (result.pid < 0) {
throw new ZygoteStartFailedEx("fork() failed");
}
return result;
} catch (IOException ex) {
zygoteState.close();
throw new ZygoteStartFailedEx(ex);
}
}

五 Zygote 程序fork

Zygote 的fork 過程參考SystemService 的啟動流程。Zygote fork 後也是通過反射的方法找到一個main 函式，這時候因為啟動的是App 程序。所以這個main 函式為ActivityThread 的main函式。

六 fork 後的新程序的 ActivityThread

fork 以後啟動ActivityThread 的main 函式，在Main 函式中完成Looper的初始化，最重要的一個呼叫就是 attach

6.1 ActivityThread attach

mgr.attachApplication(mAppThread, startSeq);

public static void main(String[] args) {

Process.setArgV0("<pre-initialized>");

Looper.prepareMainLooper();

ActivityThread thread = new ActivityThread();
thread.attach(false, startSeq);

if (sMainThreadHandler == null) {
sMainThreadHandler = thread.getHandler();
}

Looper.loop();

throw new RuntimeException("Main thread loop unexpectedly exited");
}

private void attach(boolean system, long startSeq) {
sCurrentActivityThread = this;
mSystemThread = system;
if (!system) {

android.ddm.DdmHandleAppName.setAppName("<pre-initialized>",
UserHandle.myUserId());
RuntimeInit.setApplicationObject(mAppThread.asBinder());
final IActivityManager mgr = ActivityManager.getService();
try {
mgr.attachApplication(mAppThread, startSeq);
} catch (RemoteException ex) {
throw ex.rethrowFromSystemServer();
}
} else {

}
}

6.2 AMS 的 attachApplication

AMS 的attachApplication 依次呼叫了ApplicationThread 的

1. bindApplication // 建立Application
2. scheduleTransaction(clientTransaction); // Resume Activity

AMS:
@Override
public final void attachApplication(IApplicationThread thread, long startSeq) {
synchronized (this) {
int callingPid = Binder.getCallingPid();
final int callingUid = Binder.getCallingUid();
final long origId = Binder.clearCallingIdentity();
attachApplicationLocked(thread, callingPid, callingUid, startSeq);
Binder.restoreCallingIdentity(origId);
}
}


@GuardedBy("this")
private final boolean attachApplicationLocked(IApplicationThread thread,
int pid, int callingUid, long startSeq) {


// It's possible that process called attachApplication before we got a chance to
// update the internal state.

try {
if (app.isolatedEntryPoint != null) {

} else if (app.instr != null) {
thread.bindApplication(processName, appInfo, providers,
app.instr.mClass,
profilerInfo, app.instr.mArguments,
app.instr.mWatcher,
app.instr.mUiAutomationConnection, testMode,
mBinderTransactionTrackingEnabled, enableTrackAllocation,
isRestrictedBackupMode || !normalMode, app.persistent,
new Configuration(getGlobalConfiguration()), app.compat,
getCommonServicesLocked(app.isolated),
mCoreSettingsObserver.getCoreSettingsLocked(),
buildSerial, isAutofillCompatEnabled);
} else {
thread.bindApplication(processName, appInfo, providers, null, profilerInfo,
null, null, null, testMode,
mBinderTransactionTrackingEnabled, enableTrackAllocation,
isRestrictedBackupMode || !normalMode, app.persistent,
new Configuration(getGlobalConfiguration()), app.compat,
getCommonServicesLocked(app.isolated),
mCoreSettingsObserver.getCoreSettingsLocked(),
buildSerial, isAutofillCompatEnabled);
}

} catch (Exception e) {

}

// See if the top visible activity is waiting to run in this process...
if (normalMode) {
try {
if (mStackSupervisor.attachApplicationLocked(app)) {
didSomething = true;
}
} catch (Exception e) {

}
}

return true;
}

boolean attachApplicationLocked(ProcessRecord app) throws RemoteException {
final String processName = app.processName;
boolean didSomething = false;
for (int displayNdx = mActivityDisplays.size() - 1; displayNdx >= 0; --displayNdx) {
final ActivityDisplay display = mActivityDisplays.valueAt(displayNdx);
for (int stackNdx = display.getChildCount() - 1; stackNdx >= 0; --stackNdx) {
final ActivityStack stack = display.getChildAt(stackNdx);
if (!isFocusedStack(stack)) {
continue;
}
stack.getAllRunningVisibleActivitiesLocked(mTmpActivityList);
final ActivityRecord top = stack.topRunningActivityLocked();
final int size = mTmpActivityList.size();
for (int i = 0; i < size; i++) {
final ActivityRecord activity = mTmpActivityList.get(i);
if (activity.app == null && app.uid == activity.info.applicationInfo.uid
&& processName.equals(activity.processName)) {
try {
if (realStartActivityLocked(activity, app,
top == activity /* andResume */, true /* checkConfig */)) {
didSomething = true;
}
} catch (RemoteException e) {
throw e;
}
}
}
}
}
return didSomething;
}

6.3 realStartActivityLocked

realStartActivityLocked 中建立了一個ClientTransaction。ClientTransaction 先後呼叫了下main兩個函式。

1. clientTransaction.addCallback(LaunchActivityItem.obtain(new Intent(r.intent), // LaunchActivityItem
2. clientTransaction.setLifecycleStateRequest(lifecycleItem); // ResumeActivityItem

ActivityStackSupervisor.java 

final boolean realStartActivityLocked(ActivityRecord r, ProcessRecord app,
boolean andResume, boolean checkConfig) throws RemoteException {
try {

try {
// Create activity launch transaction.
final ClientTransaction clientTransaction = ClientTransaction.obtain(app.thread,
r.appToken);
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.launchedFromPackage, task.voiceInteractor, app.repProcState, r.icicle,
r.persistentState, results, newIntents, mService.isNextTransitionForward(),
profilerInfo));
// Set desired final state.
final ActivityLifecycleItem lifecycleItem;
if (andResume) {
lifecycleItem = ResumeActivityItem.obtain(mService.isNextTransitionForward());
} else {
lifecycleItem = PauseActivityItem.obtain();
}

clientTransaction.setLifecycleStateRequest(lifecycleItem);

// Schedule transaction.
mService.getLifecycleManager().scheduleTransaction(clientTransaction);
} catch (RemoteException e) {

}
} finally {
}

return true;
}

7 Application 的建立

AMS 呼叫bindApplication，通過Binder 呼叫到新程序的ApplicationThread 類。

在ApplicationThread 類中還是傳送了要給Message 訊息到ActivityThread 類的H Handler. 最後呼叫handleBindApplication 函式

在handleBindApplication 函式中完成Application 的init.

1. 設定顯示的程序名字setAppName
2. persistent 程序在低記憶體裝置禁止硬體加速
3. AsyncTask 的執行緒池處理
4. Application Context 建立
5. 建立 Instrumentation
6. 建立 Application
7. Apk Provider 初始化

public final void bindApplication(String processName, ApplicationInfo appInfo,
List<ProviderInfo> providers, ComponentName instrumentationName,
ProfilerInfo profilerInfo, Bundle instrumentationArgs,
IInstrumentationWatcher instrumentationWatcher,
IUiAutomationConnection instrumentationUiConnection, int debugMode,
boolean enableOpenGlTrace, boolean isRestrictedBackupMode, boolean persistent,
Configuration config, CompatibilityInfo compatInfo, Map<String, IBinder> services,
Bundle coreSettings) {

AppBindData data = new AppBindData();
sendMessage(H.BIND_APPLICATION, data);
}


private void handleBindApplication(AppBindData data) {

// 1. 設定程序名
// send up app name; do this *before* waiting for debugger
Process.setArgV0(data.processName);
android.ddm.DdmHandleAppName.setAppName(data.processName,
UserHandle.myUserId());

// 2. persistent 程序在低記憶體裝置禁止硬體加速
if (data.persistent) {
// Persistent processes on low-memory devices do not get to
// use hardware accelerated drawing, since this can add too much
// overhead to the process.
if (!ActivityManager.isHighEndGfx()) {
HardwareRenderer.disable(false);
}
}

// 3. AsyncTask 的執行緒池處理
// If the app is Honeycomb MR1 or earlier, switch its AsyncTask
// implementation to use the pool executor.Normally, we use the
// serialized executor as the default. This has to happen in the
// main thread so the main looper is set right.
if (data.appInfo.targetSdkVersion <= android.os.Build.VERSION_CODES.HONEYCOMB_MR1) {
AsyncTask.setDefaultExecutor(AsyncTask.THREAD_POOL_EXECUTOR);
}

// 4. Application Context 建立
final ContextImpl appContext = ContextImpl.createAppContext(this, data.info);

// 5. 建立 Instrumentation
if (data.instrumentationName != null) {

} else {
mInstrumentation = new Instrumentation();
}


try {

// 6. 建立 Application
// If the app is being launched for full backup or restore, bring it up in
// a restricted environment with the base application class.
Application app = data.info.makeApplication(data.restrictedBackupMode, null);
mInitialApplication = app;

// don't bring up providers in restricted mode; they may depend on the
// app's custom Application class
if (!data.restrictedBackupMode) {
List<ProviderInfo> providers = data.providers;
if (providers != null) {
// 7. Provider 建立
installContentProviders(app, providers);
// For process that contains content providers, we want to
// ensure that the JIT is enabled "at some point".
mH.sendEmptyMessageDelayed(H.ENABLE_JIT, 10*1000);
}
}
} finally {
}
}

八 Activity 真正開始建立

AMS 通過binder 呼叫到App 程序

mService.getLifecycleManager().scheduleTransaction(clientTransaction);

8.1 ApplicationThread scheduleTransaction

來到 App程序的 ApplicationThread 的scheduleTransaction。然後呼叫H Handler 的handMessage 處理。過程參考 pause.

public void scheduleTransaction(ClientTransaction transaction) throws RemoteException {
ActivityThread.this.scheduleTransaction(transaction);
}

public abstract class ClientTransactionHandler {

/** Prepare and schedule transaction for execution. */
void scheduleTransaction(ClientTransaction transaction) {
transaction.preExecute(this);
sendMessage(ActivityThread.H.EXECUTE_TRANSACTION, transaction);
}
}

8.2 TransactionExecutor 的execute

TransactionExecutor 的execute 函式先後執行了

1. executeCallbacks // handleLaunchActivity
2. executeLifecycleState // handleResumeActivity

Activity 在ActivityThread 執行緒中開始執行onCreate onStart onResume.

public class TransactionExecutor {
/**
* Resolve transaction.
* First all callbacks will be executed in the order they appear in the list. If a callback
* requires a certain pre- or post-execution state, the client will be transitioned accordingly.
* Then the client will cycle to the final lifecycle state if provided. Otherwise, it will
* either remain in the initial state, or last state needed by a callback.
*/
public void execute(ClientTransaction transaction) {
final IBinder token = transaction.getActivityToken();
log("Start resolving transaction for client: " + mTransactionHandler + ", token: " + token);

executeCallbacks(transaction);

executeLifecycleState(transaction);
mPendingActions.clear();
log("End resolving transaction");
}

/** Cycle through all states requested by callbacks and execute them at proper times. */
@VisibleForTesting
public void executeCallbacks(ClientTransaction transaction) {
final List<ClientTransactionItem> callbacks = transaction.getCallbacks();

final IBinder token = transaction.getActivityToken();
ActivityClientRecord r = mTransactionHandler.getActivityClient(token);


final int size = callbacks.size();
for (int i = 0; i < size; ++i) {
final ClientTransactionItem item = callbacks.get(i);
 
item.execute(mTransactionHandler, token, mPendingActions);
item.postExecute(mTransactionHandler, token, 
}
}

/** Transition to the final state if requested by the transaction. */
private void executeLifecycleState(ClientTransaction transaction) {
final ActivityLifecycleItem lifecycleItem = transaction.getLifecycleStateRequest();

// Cycle to the state right before the final requested state.
cycleToPath(r, lifecycleItem.getTargetState(), true /* excludeLastState */);

// Execute the final transition with proper parameters.
lifecycleItem.execute(mTransactionHandler, token, mPendingActions);
lifecycleItem.postExecute(mTransactionHandler, token, mPendingActions);
}

8.3 LaunchActivityItem

public class LaunchActivityItem extends ClientTransactionItem {

@Override
public void preExecute(ClientTransactionHandler client, IBinder token) {
client.updateProcessState(mProcState, false);
client.updatePendingConfiguration(mCurConfig);
}

@Override
public void execute(ClientTransactionHandler client, IBinder token,
PendingTransactionActions pendingActions) {
Trace.traceBegin(TRACE_TAG_ACTIVITY_MANAGER, "activityStart");
ActivityClientRecord r = new ActivityClientRecord(token, mIntent, mIdent, mInfo,
mOverrideConfig, mCompatInfo, mReferrer, mVoiceInteractor, mState, mPersistentState,
mPendingResults, mPendingNewIntents, mIsForward,
mProfilerInfo, client);
client.handleLaunchActivity(r, pendingActions, null /* customIntent */);
Trace.traceEnd(TRACE_TAG_ACTIVITY_MANAGER);
}

8.4 ResumeActivityItem

public class ResumeActivityItem extends ActivityLifecycleItem {

private static final String TAG = "ResumeActivityItem";

private int mProcState;
private boolean mUpdateProcState;
private boolean mIsForward;

@Override
public void preExecute(ClientTransactionHandler client, IBinder token) {
if (mUpdateProcState) {
client.updateProcessState(mProcState, false);
}
}

@Override
public void execute(ClientTransactionHandler client, IBinder token,
PendingTransactionActions pendingActions) {
Trace.traceBegin(TRACE_TAG_ACTIVITY_MANAGER, "activityResume");
client.handleResumeActivity(token, true /* finalStateRequest */, mIsForward,
"RESUME_ACTIVITY");
Trace.traceEnd(TRACE_TAG_ACTIVITY_MANAGER);
}

@Override
public void postExecute(ClientTransactionHandler client, IBinder token,
PendingTransactionActions pendingActions) {
try {
// TODO(lifecycler): Use interface callback instead of AMS.
ActivityManager.getService().activityResumed(token);
} catch (RemoteException ex) {
throw ex.rethrowFromSystemServer();
}
}

8.5 handleLaunchActivity 和 handleResumeActivity

ActivityThread.java

@Override
public Activity handleLaunchActivity(ActivityClientRecord r,
PendingTransactionActions pendingActions, Intent customIntent) {

WindowManagerGlobal.initialize();

final Activity a = performLaunchActivity(r, customIntent);

return a;
}

public void handleResumeActivity(IBinder token, boolean finalStateRequest, boolean isForward,
String reason) {
// If we are getting ready to gc after going to the background, well
// we are back active so skip it.
unscheduleGcIdler();
mSomeActivitiesChanged = true;

// TODO Push resumeArgs into the activity for consideration
final ActivityClientRecord r = performResumeActivity(token, finalStateRequest, reason);

}