Juc-7.3-thread collaboration cyclicbarrier

Statement

CyclicBarrier Loop fence is also a thread collaboration tool , and CountDownLatch It's like , Can block a set of threads

effect

When a large number of threads cooperate with each other , Calculate different tasks separately , And when the final unified summary is needed , We can use CyclicBarrier,CyclicBarrier You can construct a staging point , When a thread executes await(), It will go to the assembly point and wait , Until all threads reach the assembly point , Then the fence will be removed , All threads start again , Continue with the remaining tasks .

Common methods

• Constructors , There are two parameters , The first is the number of waiting threads , The second is a Runnable The implementation of the
• await(): The calling thread enters the blocking state and waits

Code example

@Slf4j
public class CyclicBarrierDemo {

    public static void main(String[] args) {
        CyclicBarrier cyclicBarrier = new CyclicBarrier(5, () -> log.info(" All threads are here ..."));

        for (int i = 0; i < 5; i++) {
            new Thread(new Task(i + 1, cyclicBarrier)).start();
        }
    }

    @AllArgsConstructor
    @Slf4j
    static class Task implements Runnable{

        private int id;

        private CyclicBarrier cyclicBarrier;

        @Override
        public void run() {
            log.info(" The current thread is executing ,id:[{}]", id);
            try {
                Thread.sleep((long) (Math.random() * 10000));
                cyclicBarrier.await();
                log.info(" All threads are here , Carry on , Current thread id:{}",id);
            } catch (InterruptedException | BrokenBarrierException e) {
                e.printStackTrace();
            }
        }
    }

}

The console output is as follows :

10:40:34.645 [Thread-1] INFO com.learning.java.cooperation.CyclicBarrierDemo$Task -  The current thread is executing ,id:[2]
10:40:34.645 [Thread-0] INFO com.learning.java.cooperation.CyclicBarrierDemo$Task -  The current thread is executing ,id:[1]
10:40:34.645 [Thread-2] INFO com.learning.java.cooperation.CyclicBarrierDemo$Task -  The current thread is executing ,id:[3]
10:40:34.645 [Thread-3] INFO com.learning.java.cooperation.CyclicBarrierDemo$Task -  The current thread is executing ,id:[4]
10:40:34.645 [Thread-4] INFO com.learning.java.cooperation.CyclicBarrierDemo$Task -  The current thread is executing ,id:[5]
10:40:43.843 [Thread-4] INFO com.learning.java.cooperation.CyclicBarrierDemo -  All threads are here ...
10:40:43.843 [Thread-4] INFO com.learning.java.cooperation.CyclicBarrierDemo$Task -  All threads are here , Carry on , Current thread id:5
10:40:43.843 [Thread-2] INFO com.learning.java.cooperation.CyclicBarrierDemo$Task -  All threads are here , Carry on , Current thread id:3
10:40:43.843 [Thread-0] INFO com.learning.java.cooperation.CyclicBarrierDemo$Task -  All threads are here , Carry on , Current thread id:1
10:40:43.843 [Thread-1] INFO com.learning.java.cooperation.CyclicBarrierDemo$Task -  All threads are here , Carry on , Current thread id:2
10:40:43.843 [Thread-3] INFO com.learning.java.cooperation.CyclicBarrierDemo$Task -  All threads are here , Carry on , Current thread id:4

First of all, declare that a quantity is 5 Of CyclicBarrier, Then build 5 Threads , Call later await() Method , wait until 5 All of them await() After method , Will execute the Runnable The implementation of the , Then all threads wake up , Carry on

contrast CountDownLatch

1. The effect is different : CyclicBarrier Wait until a fixed number of threads have reached the fence position to continue execution , CountDownLatch Just wait until the counter is 0 You can continue to execute , in other words CountDownLatch For events , and CyclicBarrier Is for threads
2. Reusability is different : CountDownLatch After the countdown triggers the latch to open, it can no longer be reused , and CyclicBarrier It's reusable