Wake up a specific thread

Question

Hello All,
We have a site that has the potential of multiple users hitting our site at the same time. Each user initiates a transaction request, which goes to a controller servlet and then fires off a transaction worker. While these transaction are running, the request enters a synchronized method (a java thread monitor) that puts the request into a pool until the transaction worker completes.
My question is: how do you ensure that you only wake up the specific request that fired off the transaction worker, when the transaction worker is completed?
Any help is appreciated,
Thanks!
James

Answer 1

Have the worker invoke notifyAll() on the request object and the caller (your servlet) invoke wait() on the same object. Since one and only one client thread will exist for each request, that will work fine. Use the pool (queue?) to hold requests that have not yet been taken by a worker. The workers .wait() on the queue (or some other monitor) for work to do.
Consider using Doug Lea's excellent Executor class from his concurrency library (http://gee.cs.oswego.edu/dl/classes/EDU/oswego/cs/dl/util/concurrent/intro.html), it and the associated classes handles these kinds of need beautifully. Oh and they are also the basis of the work in JSR 166 to create a set of standardized concurrency utility classes in a future version of Java...
Chuck