共享和锁定多个线程之间的固定数量资源

Question

I have a fixed number n of identical resources that need to be shared between n or more threads. Whenever a thread needs to use a resource, it can take any available one, for which it runs an indetermininate amount of time (ie usage times are not uniform) and then release it.

What is a good Java data structure to manage this scenario? I can only think of one way to do it, which is by using a LinkedBlockingQueue and the take and put operations as locking and releasing a resource, respectively. I'd just like a suggestion from the concurrency experts:

For those who are curious: The resources that need to be shared are identical copies of a non-reentrant FORTRAN library for computing multivariate normal CDFs and moments. Spectacular numerical library, but written in an age where thread-safe code wasn't something to be worried about. In this case we make n copies of the library, where n = Runtime.getRuntime().availableProcessors() .

EDIT : I don't want to create the overhead of threads to execute this library. It is already being called from multiple threads; the calling threads should just be able to lock a resource and get on with it.

UPDATE : See https://stackoverflow.com/a/19039878/586086 for the motivation and the implementation.

Answer 1

The pattern you're describing is a resource pool . A thread-safe queue is a reasonable way to handle the situation when the resources are fairly simple, though you might also consider a pool library such as pool4j .

Answer 2

Create a singleton class with a list of fixed resource, and associated flag to mark each resource as available or unavailable, and 2 synchronized methods, something like:

synchronized Resource getResource(){
   find an unavailable resource, mark it as unavailable and return it
}

synchronized int returnResource(Resource r){
   find the matching resource on list and mark it as available.
}