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javaconcurrencyblocking

Implement a blocking function call in Java

What is the recommended / best way to implement a blocking function call in Java, that can be later unblocked by a call from another thread?

Basically I want to have two methods on an object, where the first call blocks any calling thread until the second method is run by another thread:

public class Blocker {

  /* Any thread that calls this function will get blocked */
  public static SomeResultObject blockingCall() {
     // ...      
  }

  /* when this function is called all blocked threads will continue */
  public void unblockAll() {
     // ...
  }

}

The intention BTW is not just to get blocking behaviour, but to write a method that blocks until some future point when it is possible to compute the required result.

Solution

  • You can use a CountDownLatch.

    latch = new CountDownLatch(1);

    To block, call:

    latch.await();

    To unblock, call:

    latch.countDown();