Exception: java.util.ConcurrentModificationException on 1.1.1-rc1

[megataps]

I got this crash report on the latest build 1.1.1-rc1

Fatal Exception: java.util.ConcurrentModificationException
at java.util.ArrayList$ArrayListIterator.next(ArrayList.java:573)
at com.android.volley.toolbox.ImageLoader$4.run(SourceFile:491)
at android.os.Handler.handleCallback(Handler.java:739)
at android.os.Handler.dispatchMessage(Handler.java:95)
at android.os.Looper.loop(Looper.java:135)
at android.app.ActivityThread.main(ActivityThread.java:5318)
at java.lang.reflect.Method.invoke(Method.java)
at java.lang.reflect.Method.invoke(Method.java:372)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:922)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:717)

[hero0812]

do not modify the ArrayList when it is being traversed

[jpd236]

Assuming the line in question is indeed line 491 of ImageLoader.java:

for (ImageContainer container : bir.mContainers) {

then the issue would be something mutating mContainers during this iteration.

This line of code always runs on the main thread (it is posted to a main thread handler). There are four other methods which mutate mContainers, but as far as I can tell, all of these are only called by methods which first invoke Threads.throwIfNotOnMainThread(), and so would throw a different failure if they were being called here on a different thread.

There are thus only two possibilities I can think of:

• Something inside this loop is causing the list to be mutated. The ImageListeners created by Volley don't appear to ever do this. Are you using a custom ImageListener, and if so, does that ImageListener ever call ImageContainer#cancelRequest or ImageLoader#get?
• This isn't actually the line of code that's crashing. (Proguard appears to be involved, since it says "SourceFile" rather than the actual file).

I don't think this is a regression from older builds. Sounds like this was a one-off crash reported in the wild? Do you have more information (and ideally code) showing how you are using ImageLoader?

[jpd236]

https://stackoverflow.com/questions/35479128/volley-image-loader-concurrentmodificationexception seems to be a similar crash with sample code in the wild.

[javad-vovin]

We have a similar exception.
It's very hard to reproduce, but the scenario is ImageContainer cancel request but handler in batchResponse is still processing mBatchedResponses, when this happen java.util.ConcurrentModificationException will occurred.

[joebowbeer]

CME is most often thrown from a single thread, despite the name, so that seems most likely here.

These iterators are both in flight when a listener may be called on the same thread:

for (BatchedImageRequest bir : mBatchedResponses.values()) {
    for (ImageContainer container : bir.mContainers) {

Maybe the problem can be avoided by switching to indexed loops:

for (int i = 0; i < bir.mContainers.size(); i++) {
    ImageContainer container = bir.mContainers.get(i);

Or copying to an array before iterating, depending on the desired behavior.

The outer batchedResponses loop should also be protected from concurrent modification in the same way. An invoked listener might be able to reach:

mBatchedResponses.remove(mCacheKey)