Broadcast发送流程分析

╰半橙微兮° 2023-07-11 11:16 8阅读 0赞

Android Source Tools : androidxref.com

# Original stack trace: #

android.app.RemoteServiceException : can’t deliver broadcast  
at android.app.ActivityThread H . h a n d l e M e s s a g e ( A c t i v i t y T h r e a d . j a v a : 2038 ) a t a n d r o i d . o s . H a n d l e r . d i s p a t c h M e s s a g e ( H a n d l e r . j a v a : 107 ) a t a n d r o i d . o s . L o o p e r . l o o p ( L o o p e r . j a v a : 214 ) a t a n d r o i d . a p p . A c t i v i t y T h r e a d . m a i n ( A c t i v i t y T h r e a d . j a v a : 7682 ) a t j a v a . l a n g . r e f l e c t . M e t h o d . i n v o k e ( M e t h o d . j a v a ) a t c o m . a n d r o i d . i n t e r n a l . o s . R u n t i m e I n i t H.handleMessage(ActivityThread.java:2038) at android.os.Handler.dispatchMessage(Handler.java:107) at android.os.Looper.loop(Looper.java:214) at android.app.ActivityThread.main(ActivityThread.java:7682) at java.lang.reflect.Method.invoke(Method.java) at com.android.internal.os.RuntimeInit H.handleMessage(ActivityThread.java:2038)atandroid.os.Handler.dispatchMessage(Handler.java:107)atandroid.os.Looper.loop(Looper.java:214)atandroid.app.ActivityThread.main(ActivityThread.java:7682)atjava.lang.reflect.Method.invoke(Method.java)atcom.android.internal.os.RuntimeInitMethodAndArgsCaller.run(RuntimeInit.java:516)  
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:950)

conclusion: By the above Log information and the following process analysis, we can only conclude that when Step7 was about to distribute the broadcast to the registered BroadcastReceiver, the remote Binder was found dead, but we don’t know why

--------------------

# eg. Android SDK 29 source code for analysis #

First. We have found the problem log occurs in the android system code

com.android.server.am.BroadcastQueue.java Line 600

“app.scheduleCrash(“can’t deliver broadcast”);” in the method “performReceiveLocked”

I Found Google developers offering this code comments here (“Failed to call into the process. It’s either dying or wedged. Kill It gently”)

In order to understand their approach, I analyzed the transmission process of Broadcast. The process analysis is as follows

--------------------

Step1. Context.sendBroadcast(Intent) \[can other app\] -> in fact is ContextImpl.sendBroadcast(Intent)  
function body contracted version\{  
…  
intent.prepareToLeaveProcess(this);  
ActivityManager.getService().broadcastIntent(…)  
…  
\}  
This operation will leave current app process, calling AMS is broadcast

--------------------

Step2. ActivityManagerService.broadcastIntent(…) -> code final call method “ActivityManagerService.broadcastIntentLocked”  
function body contracted version\{  
…  
// Figure out who all will receive this broadcast.  
List receivers = null;  
List registeredReceivers = null;  
// Need to resolve the intent to interested receivers…  
registeredReceivers = mReceiverResolver.queryIntent(intent,  
resolvedType, false /*defaultOnly*/, userId);  
…  
…  
BroadcastQueue queue = broadcastQueueForIntent(intent);  
BroadcastRecord r = new BroadcastRecord(…);

queue.enqueueOrderedBroadcastLocked®;  
queue.scheduleBroadcastsLocked();  
…  
\}  
This operation will find the receivers of the broadcast  
Get the foreground or background queues from AMS  
Construct a BroadcastRecord class object and put it in a BroadcastQueue(This is our focus class, due to this bug that appears here)

--------------------

Step3. BroadcastQueue.scheduleBroadcastsLocked()  
function body contracted version\{  
// Set when we current have a BROADCAST\_INTENT\_MSG in flight.  
if (mBroadcastsScheduled) \{  
return;  
\}  
mHandler.sendMessage(mHandler.obtainMessage(BROADCAST\_INTENT\_MSG, this));  
mBroadcastsScheduled = true;  
\}  
We can see that this is just to activate the handler if it’s not already activated, because the broadcast we are sending is already waiting in the queue

--------------------

Step4. BroadcastQueue.BroadcastHandler\#handleMessage()  
function body contracted version\{  
…  
switch (msg.what) \{  
case BROADCAST\_INTENT\_MSG: \{  
processNextBroadcast(true);  
\} break;  
case BROADCAST\_TIMEOUT\_MSG: \{  
synchronized (mService) \{  
broadcastTimeoutLocked(true);  
\}  
\} break;  
\}  
…  
\}  
From the code we can clearly see that the final call to processNextBroadcast() method

--------------------

Step5. BroadcastQueue\#processNextBroadcast() -> final call to processNextBroadcastLocked()  
function body contracted version\{  
// First, deliver any non-serialized broadcasts right away.  
while (mParallelBroadcasts.size() > 0) \{  
…  
r = mParallelBroadcasts.remove(0);  
r.dispatchTime = SystemClock.uptimeMillis();  
r.dispatchClockTime = System.currentTimeMillis();  
final int N = r.receivers.size();  
for (int i=0; i<N; i++) \{  
Object target = r.receivers.get(i);  
deliverToRegisteredReceiverLocked(r, (BroadcastFilter)target, false, i);  
\}  
addBroadcastToHistoryLocked®;  
…  
\}  
\}  
We see the real distribution of the broadcast

--------------------

Step6. BroadcastQueue\#deliverToRegisteredReceiverLocked()  
function body contracted version\{  
…  
performReceiveLocked(filter.receiverList.app, filter.receiverList.receiver,  
new Intent(r.intent), r.resultCode, r.resultData,  
r.resultExtras, r.ordered, r.initialSticky, r.userId);  
…  
\}  
Send this broadcast

--------------------

Step7. BroadcastQueue\#performReceiveLocked()\[★★★bug happend method body★★★\]

function body compelete verion\{  
//Send the intent to the receiver asynchronously using one-way binder calls.  
if (app != null) \{  
if (app.thread != null) \{  
// If we have an app thread, do the call through that so it is  
// correctly ordered with other one-way calls.  
try \{  
app.thread.scheduleRegisteredReceiver(receiver, intent, resultCode,  
data, extras, ordered, sticky, sendingUser, app.getReportedProcState());  
// TODO: Uncomment this when (b/28322359) is fixed and we aren’t getting  
// DeadObjectException when the process isn’t actually dead.  
//\} catch (DeadObjectException ex) \{  
// Failed to call into the process. It’s dying so just let it die and move on.  
// throw ex;  
\} catch (RemoteException ex) \{  
// Failed to call into the process. It’s either dying or wedged. Kill it gently.  
synchronized (mService) \{  
Slog.w(TAG, "Can’t deliver broadcast to " + app.processName  
\+ " (pid " + app.pid + “). Crashing it.”);  
app.scheduleCrash(“can’t deliver broadcast”);  
\}  
throw ex;  
\}  
\} else \{  
// Application has died. Receiver doesn’t exist.  
throw new RemoteException(“app.thread must not be null”);  
\}  
\}  
\}  
This bug is happend here, we will go to next method

--------------------

Step8. ActivityThread\#scheduleRegisteredReceiver(IIntentReceiver receiver,…)  
function body compelete verion\{  
updateProcessState(processState, false);  
receiver.performReceive(…);  
\}  
receiver is IIntentReceiver impl

--------------------

Step9. LoadedApk.ReceiverDispatcher.InnerReceiver\#performReceive()  
function body compelete verion\{  
if (rd != null) \{  
// Rc. rd -> class LoadedApk.ReceiverDispatcher object  
rd.performReceive(…);  
\} else \{  
// The activity manager dispatched a broadcast to a registered  
// receiver in this process, but before it could be delivered the  
// receiver was unregistered. Acknowledge the broadcast on its  
// behalf so that the system’s broadcast sequence can continue.  
if (ActivityThread.DEBUG\_BROADCAST) Slog.i(ActivityThread.TAG,  
“Finishing broadcast to unregistered receiver”);  
IActivityManager mgr = ActivityManager.getService();  
try \{  
mgr.finishReceiver(this, resultCode, data, extras, false, intent.getFlags());  
\} catch (RemoteException e) \{  
throw e.rethrowFromSystemServer(); // Rc. We need to think about this place  
\}  
\}  
\}  
Normally we want rd to be valid

--------------------

Step10. LoadedApk.ReceiverDispatcher\#performReceive()  
function body contracted version\{  
…  
final Args args = new Args(intent, resultCode, data, extras, ordered, sticky, sendingUser);  
…  
mActivityThread.post(args.getRunnable())  
…  
\}

--------------------

Step11. LoadedApk.Args\#getRunnable()  
function body contracted version\{  
…  
ClassLoader cl = mReceiver.getClass().getClassLoader();  
intent.setExtrasClassLoader(cl);  
intent.prepareToEnterProcess();  
setExtrasClassLoader(cl);  
receiver.setPendingResult(this);  
receiver.onReceive(mContext, intent);  
…  
\}  
Done send broadcast