How to use CyclicBarrier for high concurrency in Java

CyclicBarrier in Java is a synchronization tool that allows multiple threads to wait at a barrier until all threads reach the barrier before execution can continue. CyclicBarrier can be used to coordinate the execution of multiple threads so that they can execute simultaneously at a certain point.

CyclicBarrier is a synchronization tool in Java that allows multiple threads to wait at a barrier point until all threads reach that point before they can continue execution. CyclicBarrier can be used to coordinate the execution of multiple threads so that they can execute simultaneously at a certain point.

Usage

The basic usage of CyclicBarrier is as follows:

import java.util.concurrent.BrokenBarrierException;
import java.util.concurrent.CyclicBarrier;

public class CyclicBarrierExample {

    public static void main(String[] args) {
        int n = 3;
        CyclicBarrier barrier = new CyclicBarrier(n, new Runnable() {
            public void run() {
                System.out.println("All threads have reached the barrier");
            }
        });

        Thread t1 = new Thread(new MyRunnable(barrier), "Thread 1");
        Thread t2 = new Thread(new MyRunnable(barrier), "Thread 2");
        Thread t3 = new Thread(new MyRunnable(barrier), "Thread 3");

        t1.start();
        t2.start();
        t3.start();
    }

    static class MyRunnable implements Runnable {
        private final CyclicBarrier barrier;

        public MyRunnable(CyclicBarrier barrier) {
            this.barrier = barrier;
        }

        public void run() {
            try {
                System.out.println(Thread.currentThread().getName() + " is waiting at the barrier...");
                barrier.await();
                System.out.println(Thread.currentThread().getName() + " has crossed the barrier");
            } catch (InterruptedException e) {
                e.printStackTrace();
            } catch (BrokenBarrierException e) {
                e.printStackTrace();
            }
        }
    }
}

In this example, we create a CyclicBarrier object, which needs to wait for 3 threads to reach the barrier point. When all threads reach the barrier point, a callback function will be triggered and a message will be printed.

We create 3 threads and pass them to a custom Runnable object. In each thread's run method, we first print a message indicating that the thread is waiting for the barrier point. Then call the barrier.await() method to add the thread to the waiting queue. Execution will not continue until all threads reach the barrier point. At the end, we print a message indicating that the thread has crossed the barrier point.

The running results of the above code are as follows:

Thread 1 is waiting at the barrier...
Thread 3 is waiting at the barrier...
Thread 2 is waiting at the barrier...
All threads have reached the barrier
Thread 2 has crossed the barrier
Thread 1 has crossed the barrier
Thread 3 has crossed the barrier

It can also be seen from the above code that CyclicBarrier also supports an optional callback function. After all threads reach the barrier point, the specified callback function will be called. In the above example, when all threads reach the barrier point When the time comes, the callback function will be executed to indicate that the barrier point has been reached.

CyclicBarrier also supports a more advanced usage, which is to perform some additional operations while waiting for the thread to reach the barrier point. This can be achieved through the return value of the await method, as shown below:

int index = barrier.await();
if (index == 0) {
    // 执行额外的操作
}

In this example, the return value of the await method indicates the position of the thread in the waiting queue. If the return value is 0, it means The current thread is the last thread to reach the barrier point and can perform some additional operations, such as doing some finishing work such as data cleaning.

Notes

When using CyclicBarrier in Java, you need to pay attention to the following points:

1. The counter of CyclicBarrier is reusable, that is, when all After all threads reach the barrier point, the counter will be reset to its initial value and can be used again. If an exception occurs during waiting, the counter will be reset and all waiting threads will throw BrokenBarrierException.

2. If the number of waiting threads exceeds the initial value of the counter when using CyclicBarrier, all threads will wait forever. Therefore, when using CyclicBarrier, you need to ensure that the number of waiting threads does not exceed the initial value of the counter.

3. The callback function of CyclicBarrier is executed when the last thread reaches the barrier point. Therefore, The operations performed in the callback function should be thread-safe, otherwise it may Can lead to unpredictable results.

4.CyclicBarrier can be used to coordinate the execution of multiple threads so that they can execute simultaneously at a certain point. **However, if the order of execution between threads is important to the correctness of the program, then CyclicBarrier may not be the best choice. **In this case, it may be necessary to use other synchronization tools such as CountDownLatch or Semaphore.

5. The performance of CyclicBarrier may be affected by the number of waiting threads and the initial value of the counter. **If the number of waiting threads is large, or the initial value of the counter is large, performance degradation may occur. **Therefore, when using CyclicBarrier, it needs to be adjusted according to the actual situation.

In short, when using CyclicBarrier in Java, various situations need to be carefully considered to ensure the correctness and performance of the program.

The above is the detailed content of How to use CyclicBarrier for high concurrency in Java. For more information, please follow other related articles on the PHP Chinese website!