Thread pool that binds tasks for a given ID to the same thread

Question

Are there any implementations of a thread pool (in Java) that ensures all tasks for the same logical ID are executed on the same thread?

The logic I\'m after is if t

Answer 1

Our approach is similar to what is in the update of the original question. We have a wrapper class that is a runnable that contains a queue (LinkedTransferQueue) which we call a RunnableQueue. The runnable queue has the basic API of:

public class RunnableQueue implements Runnable
{
  public RunnableQueue(String name, Executor executor);
  public void run();

  public void execute(Runnable runnable);
}

When the user submits the first Runnable via the execute call the RunnableQueue enqueues itself on the executor. Subsequent calls to execute get queued up on the queue inside the RunnableQueue. When the runnable queue get executed by the ThreadPool (via its run method) it starts to "drain" the internal queue by serially executing the runnables one by one. If execute is called on the RunnableQueue while it is executing, the new runnables simply get appended to the internal queue. Once the queue is drained, the run method of the runnable queue completes and it "leaves" the executor pool. Rinse repeat.

We have other optimizations that do things like only let some number of runnables run (e.g. four) before the RunnableQueue re-posts itself to the executor pool.

The only really tricky bit inside and it isn't that hard) is to synchronize around when it is posted to the executor or not so that it doesn't repost, or miss when it should post.

Overall we find this to work pretty well. The "ID" (semantic context) for us is the runnable queue. The need we have (i.e. a plugin) has a reference to the RunnableQueue and not the executor pool so it is forced to work exclusively through the RunnableQueue. This not only guarantees all accesses are serially sequence (thread confinement) but lets the RunnableQueue "moderate" the plugin's job loading. Additionally, it requires no centralized management structure or other points of contention.