How to implement simple threading with a fixed number of worker threads
concurrency, java, multithreading
Solution
I think that Executors.newFixedThreadPool fits your requirements. There are a number of different ways to use the resulting ExecutorService, depending on whether you want a result returned to the main thread, or whether the task is totally self-contained, and whether you have a collection of tasks to perform up front, or whether tasks are queued in response to some event.
Collection<YourTask> tasks = new ArrayList<YourTask>();
YourTask yt1 = new YourTask();
...
tasks.add(yt1);
...
ExecutorService exec = Executors.newFixedThreadPool(5);
List<Future<YourResultType>> results = exec.invokeAll(tasks);
Alternatively, if you have a new asynchronous task to perform in response to some event, you probably just want to use the ExecutorService's simple `execute(Runnable)` method.
Problem
I'm looking for the simplest, most straightforward way to implement the following: - The main program instantiates worker threads to do a task. - Only `n` tasks can be running at once. - When `n` is reached, no more workers are started until the count of running threads drops back below `n`.