ConcurrentModification Exception in ArrayList

Question

I know there are many questions asked on this but in my case i have it in a synchronised block and i am sure that nobody will be changing my array list.. But still i get this exception SOMETIMES if i am using for-each loop.. Why ?

Here is my code snippet

    final static Object mLock = new Object();
private static ArrayList<ConnectionAndAuthCallback> mCallbacks;
private void callAuthCallbacks() {
        synchronized (mLock) {

            if (mCallbacks != null)
                for (ConnectionAndAuthCallback calback : mCallbacks) { //here i get exception
                    calback.onAuthentication(mToken, calback.intent);
                }
        }
    }

here is the code i do on Callback

@Override
            public void onAuthentication(String token, Intent intent) {
                web.loadUrl("xyz.com");
                //unregister so that we wong get any exception or some more callbacks
                SameClass.unRegisterAuthCallbacks(this); 
            }

and in Unregister function

public static void unRegisterAuthCallbacks(ConnectionAndAuthCallback callback) {
        synchronized (mLock) {

            if (mCallbacks != null)
                if (mCallbacks.contains(callback)) {
                    mCallbacks.remove(callback); // This causing problem ?? In same thread "syncronised" wont work ??
                }
        }
    }

Seems you are on wrong track. This code block should not cause this exception. — Pankaj Kumar
– Pankaj Kumar, Commented Jun 16, 2014 at 5:28
Where else in your code do you use mCallbacks? Are you iterating through mCallbacks at some point prior to the call to callAuthCallbacks()? — Alex Lockwood
– Alex Lockwood, Commented Jun 16, 2014 at 5:29
You could always create your own ArrayList subclass that logs whenever the list is changed and by whom, and substitute that in. That's always a fun debugging technique. — awksp
– awksp, Commented Jun 16, 2014 at 5:31
Yes, mCallbacks gets iterated through in some other places too but they are too inside sync block — Charan Pai
– Charan Pai, Commented Jun 16, 2014 at 5:32
Well, that's strange. Doesn't seem like the exception should be happening, and if none of us can reproduce your problem, helping you will be somewhat difficult... Try the ArrayList subclass thing and see if that helps? — awksp
– awksp, Commented Jun 16, 2014 at 5:35

Community · Accepted Answer · 2017-05-23 12:27:10Z

1

You can't perform modifications on an ArrayList or remove() in this case that you are currently reading out of or looping through. Use iterators instead.

Check out this link. And this link.

edited May 23, 2017 at 12:27

CommunityBot

11 silver badge

answered Jun 16, 2014 at 5:54

Ryhan

1,8851 gold badge18 silver badges22 bronze badges

Sign up to request clarification or add additional context in comments.

1 Comment

Charan Pai Over a year ago

I had gone through this before i asked this question. And obiously it solves the problem.

Charan Pai · Accepted Answer · 2014-06-22 15:22:43Z

0

Answer was, In the same thread synchronised(){} wont work. Even if you think it works then there might be a dead lock.

In my case i was removing callback object from ArrayList in the same thread where i called callback.

answered Jun 22, 2014 at 15:22

Charan Pai

2,3265 gold badges32 silver badges45 bronze badges

Collectives™ on Stack Overflow

ConcurrentModification Exception in ArrayList

2 Answers 2

1 Comment

Comments

Your Answer

Linked

Hot Network Questions

Collectives™ on Stack Overflow

2 Answers 2

1 Comment

Comments

Your Answer

Sign up or log in

Post as a guest

Linked

Related