InvalidOperationException in DotNetMQ halts all communication

[abhithakur88]

Hi.

Recently in my production environment all the machines stopped sending/receiving messages via DotNetMQ. One machine had following exception in logs:

WARN  2018-04-12 15:18:25,028 [22   ] MDS.Communication.MDSRemoteApplication   - Collection was modified after the enumerator was instantiated.
System.InvalidOperationException: Collection was modified after the enumerator was instantiated.
   at System.Collections.Generic.LinkedList`1.Enumerator.MoveNext()
   at MDS.Communication.MDSRemoteApplication.MessageDeliverer.AsynchronMessageControlTimer_Elapsed(Object state)

This happened 3 to 4 times recently and every time one machine has above Dotnetmq logs. The setup is point-to-point in-memory non-persistent.

I checked the DotnetMQ code. Inside method MessageDeliverer.AsynchronMessageControlTimer_Elapsed(), there is a foreach loop trying to modify the collection which is causing this exception. Following is the extraction:

foreach (var connectedCommunicator in _remoteApplication._communicators)
{
    ...
    //Send communicator to end of the _receiverCommunicators list.
    _remoteApplication._communicators.Remove(connectedCommunicator);
    _remoteApplication._communicators.AddLast(connectedCommunicator);
}

Can you please help to describe what this code is trying to achieve. Can you please also help fixing the above code.

Thanks
Abhishek

[hikalkan]

It's strange. I don't know how it was working :) It obviously changes the collection items inside a loop, which is not possible.

You can send a PR to solve the problem, if you can.

[abhithakur88]

You can send a PR to solve the problem, if you can.
Not sure about that. It says "nothing to compare. cannot create pull request".

Anyways, I tried fixing that using a copy of the collection.

MDSRemoteApplication.SubClasses.zip