Deadlock when 2 threads write to the same HashMap

You probably know that the java.util collections are not thread-safe (with the exception of Vector).

Today I encountered a problem when 2 threads which each process their own asynchronous data stream write to the same static HashMap via a static method.

The problem exhibits itself as a code freeze on the threads involved but sending the kill -3 signal to the java pid (or the CTRL-Break if you are in a Windows command prompt) to get a thread dump does not identify any deadlocks.

The 2 threads involved both show themselves stuck in the HashMap.put() method.

The quick solution if you are using Java 1.5 or later is to substitute java.util.concurrent.ConcurrentHashMap for HashMap.