Controlling Task execution order with ExecutorService

user_164197 0
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I have a process which delegates asynch tasks to a pool of threads. I need to ensure that certain tasks are executed in order. So for example

Tasks arrive in order

Tasks a1, b1, c1, d1 , e1, a2, a3, b2, f1

Tasks can be executed in any order except where there is a natural dependancy, so a1,a2,a3 must be processed in that order by either allocating to the same thread or blocking these until I know the previous a# task was completed.

Currently it doesn't use the Java Concurrency package, but I'm considering changing to take avantage of the thread management.

Does anyone have a similar solution or suggestions of how to achieve this

executorservice concurrency java
8 Answers

When you submit a Runnable or Callable to an ExecutorService you receive a Future in return. Have the threads that depend on a1 be passed a1's Future and call Future.get(). This will block until the thread completes.

So:

ExecutorService exec = Executor.newFixedThreadPool(5);
Runnable a1 = ...
final Future f1 = exec.submit(a1);
Runnable a2 = new Runnable() {
  @Override
  public void run() {
    f1.get();
    ... // do stuff
  }
}
exec.submit(a2);

and so on.

cletus_183930
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