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I have a problem that I want to solve. I have one thread that must wait a number of a variable number of async threads to finish their execution finishes and after that, It must execute and again stay in the wait state until the other threads finish their execution.

Example:

Thread A waits until Threads B and C finishes their execution. After that Thread A must be executed and other threads should wait. This is a cycle that repeats n times.

ThreadA{
   public void run(){
      while(true){
         if(queue.peek() % 2 == 0){
            phaser.arriveAndAwaitAdvance();
            doStuff();
         }
      }
   }
}
ThreadB{
   public void run(){
      while(true){
          if(queue.peek() % 2 == 0){
             doStuff();
             phaser.arrive();
          }
      }
   }
}

Thread C has the same pseudocode as Thread B.

I need synchronized something like this: Thread A must executed only after Thread B and Thread C perform their execution and Thread B and Thread C must wait Thread A finalize its execution.

I tryied using Phaser as mentioned in code above with Phaser but I din't get the result expected.

Could someone give an example?

I am using Java 8 and I looking for a resettable form of CountDownLatch, maybe using phaser.

Domenico Schettini Filho
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    I'm not sure I understood the case. Can you please specify an exact End-to-end scenario? – javadev Mar 14 '21 at 03:20
  • The scenario is as written .. Thread B and Thread C must complete their work, then Thread A will run, when Thread A finishes it starts again, thread B and thread C must complete their work, then thread A will run... The "N" times is forever, or bounded ?? – Mr R Mar 14 '21 at 07:01
  • Lots of [good ideas here](https://ducmanhphan.github.io/2020-03-20-Waiting-threads-to-finish-completely-in-Java/) – Mr R Mar 14 '21 at 07:02
  • You need to be more specific in your scenario. Are threads running in a loop ? can you provide some actually pseudo code or something – dreamcrash Mar 14 '21 at 09:57
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    Both [`CyclicBarrier`](https://docs.oracle.com/en/java/javase/15/docs/api/java.base/java/util/concurrent/CyclicBarrier.html) and [`Phaser`](https://docs.oracle.com/en/java/javase/15/docs/api/java.base/java/util/concurrent/Phaser.html) will do what you need, they even support actions on countdown / phase advance. `CyclicBarrier` is older and slower, while `Phaser` is new, fast, and supports a richer API. That said, each has their place. – Petr Janeček Mar 14 '21 at 17:45

0 Answers0