ConcurrentModification Exception

Classic Servoy
1

I have a a batch processe called packet_processor running on a Servoy 4.1 server (Mac OSX, Java 1.5) It receives/sends/processes udp packets using the udp plugin.

This process periodically generates a ConcurrentModification exception. Usually it just keeps working despite the error, but recently this error stopped it from processing packets, which eventually lead to “OutOfMemoryError: Java heap space” as unprocessed packet data accumulated in memory, which eventually brought the server down altogether. Interesting to note that scheduled jobs in the packet_processor continued running normally, but the main packet processing loop just stopped running.

I’d like to know what this ConcurrentModification exception means and how can I avoid it? And if I can’t avoid it, would it be safe for me to use the robot plugin to automatically stop and restart the batch process when the error is encountered?

Thank you.

2

An Explanation:

This exception may be thrown by methods that have detected concurrent modification of an object when such modification is not permissible.

For example, it is not generally permissible for one thread to modify a Collection while another thread is iterating over it. In general, the results of the iteration are undefined under these circumstances. Some Iterator implementations (including those of all the general purpose collection implementations provided by the JRE) may choose to throw this exception if this behavior is detected. Iterators that do this are known as fail-fast iterators, as they fail quickly and cleanly, rather that risking arbitrary, non-deterministic behavior at an undetermined time in the future.

Note that this exception does not always indicate that an object has been concurrently modified by a different thread. If a single thread issues a sequence of method invocations that violates the contract of an object, the object may throw this exception. For example, if a thread modifies a collection directly while it is iterating over the collection with a fail-fast iterator, the iterator will throw this exception.

3

amcgilly:
I have a a batch processe called packet_processor running on a Servoy 4.1

Please file a bug report, those error should not never happen in the Servoy code, attach you servoy_log.txt file to the case
BTW are you sure you assigned enoug memory to the Servoy server? or left the default? (OutOfMemoryError will couse all kind of strange errors)