How to use barriers to achieve thread synchronization in Java concurrent programming?

A barrier is a synchronization tool used to make a group of threads wait for all threads to reach a specified point before continuing execution. Barriers can be created using java.util.concurrent.CyclicBarrier, and each thread joins the barrier and waits for other threads by calling the await() method. When all threads have reached the barrier, they continue execution. Barriers can be used to ensure that no subsequent operations are performed until all threads have completed their calculations.

Using barriers to achieve thread synchronization in Java concurrent programming

The barrier is a synchronization tool in concurrent programming that allows a The group thread waits for all threads to reach a certain point before continuing execution. This is useful in certain scenarios, such as performing subsequent operations after all threads have completed initialization.

Create Barrier

We can use the java.util.concurrent.CyclicBarrier class to create a barrier. The constructor of this class receives an integer parameter representing the number of threads in the barrier.

CyclicBarrier barrier = new CyclicBarrier(4);

Using Barrier

To use a barrier, each thread must call the await() method. This method will block the thread until all threads in the barrier have called the await() method. When all threads have reached the barrier, they continue execution.

for (int i = 0; i < 4; i++) {
    new Thread(() -> {
        try {
            barrier.await();
        } catch (InterruptedException | BrokenBarrierException e) {
            e.printStackTrace();
        }
    }).start();
}

Practical Case

Suppose we have a group of threads that need to generate a report that can only be summarized when all threads have completed their calculations. We can use a barrier to ensure that aggregation does not start until all threads have completed their calculations.

cyclicBarrier.await();
// 汇总结果并生成报告

Notes

• Barriers are a synchronization tool that can slow down a program and should be considered carefully when used.
• The barrier does not support interruption, so when a thread is blocked in the barrier, other threads cannot interrupt it.
• The barrier supports timeout. If a thread does not reach the barrier within the specified time, the barrier will throw a BrokenBarrierException exception and all other threads will continue to execute.

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