How to implement simple threading with a fixed number of worker threads
I'm looking for the simplest, most straightforward way to implement the following:
n
tasks can be running at once. n
is reached, no more workers are started until the count of running threads drops back below n
. 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.
/* Get an executor service that will run a maximum of 5 threads at a time: */
ExecutorService exec = Executors.newFixedThreadPool(5);
/* For all the 100 tasks to be done altogether... */
for (int i = 0; i < 100; i++) {
/* ...execute the task to run concurrently as a runnable: */
exec.execute(new Runnable() {
public void run() {
/* do the work to be done in its own thread */
System.out.println("Running in: " + Thread.currentThread());
}
});
}
/* Tell the executor that after these 100 steps above, we will be done: */
exec.shutdown();
try {
/* The tasks are now running concurrently. We wait until all work is done,
* with a timeout of 50 seconds: */
boolean b = exec.awaitTermination(50, TimeUnit.SECONDS);
/* If the execution timed out, false is returned: */
System.out.println("All done: " + b);
} catch (InterruptedException e) { e.printStackTrace(); }
Executors.newFixedThreadPool(INT)
Executor executor = Executors.newFixedThreadPool(n);
Runnable runnable = new Runnable() {
public void run() {
// do your thing here
}
}
executor.execute(runnable);
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