Question

I am running a multithreaded application with 3 threads:

• Main Thread – Vector List to store Objects
• AdderThread – Add Objects to this Vector List
• RemoverThread – Remove Objects with vectorList.clear() method (synchronized)

Application runs fine but after few hours it gives OutOfMemoryError.

I generated Heap dump and analysed with eclipse MAT which shows vectorList class taking all the memory.

Does clear method free memory which was occupied by individual objects ?

How to fix this?

Answer 1

If you are adding tasks faster than you are freeing them, you will get an OutOfMemoryError as your Vector will grow to the limit of your memory.

Instead of using a Vector for a work queue, I suggest using a BlockingQueue from the concurrency libraries.

e.g.

BlockingQueue<Work> queue = new ArrayBlockingQueue<>(MAX_TASKS_WAITING);

AdderThread calls queue.put(work); // blocks if the queue is full

RemoverThread call queue.take(); // blocks if there is nothing to do.

In fact it would be much simpler to use an ExecutorService as this combines a work queue with a thread pool. You submit tasks to the executor and it processes them. This avoids the need to write any code for the RemoverThread as such.