Java uses the join() function of the Thread class to implement thread synchronization

Java uses the join() function of the Thread class to implement thread synchronization

In Java multi-threaded programming, thread synchronization is an important concept. In some scenarios, we want threads to execute in a specific order, or to wait for other threads to finish executing before continuing. Java's Thread class provides the join() function to implement thread synchronization.

The join() function is a method provided by the Thread class. Its function is to wait for the thread to complete execution before continuing. When a thread calls the join() method of another thread, it will be blocked until the target thread completes execution, and then execution can continue.

The following is a sample code that uses the join() function to achieve thread synchronization:

public class JoinExample {
    public static void main(String[] args) throws InterruptedException {
        Thread t1 = new Thread(new MyRunnable(), "Thread1");
        Thread t2 = new Thread(new MyRunnable(), "Thread2");
        
        // 启动线程
        t1.start();
        t2.start();
        
        // 使用join()函数实现线程同步
        t1.join();
        t2.join();
        
        System.out.println("All threads have finished executing.");
    }
}

class MyRunnable implements Runnable{
    @Override
    public void run() {
        System.out.println(Thread.currentThread().getName() + " is running.");
        try {
            Thread.sleep(2000);
        } catch (InterruptedException e) {
            e.printStackTrace();
        }
        System.out.println(Thread.currentThread().getName() + " has finished executing.");
    }
}

In the above code, we created two threads t1 and t2, and used the start of the Thread class () method starts them. Then, use the join() method to achieve thread synchronization, that is, wait for the t1 and t2 threads to complete execution before continuing to execute the main thread. Finally, print out the message that all threads have completed execution.

Run the above code, you will get the following output:

Thread1 is running.
Thread2 is running.
Thread1 has finished executing.
Thread2 has finished executing.
All threads have finished executing.

As can be seen from the output, the t1 and t2 threads execute alternately, and the main thread continues execution after they have completed their execution.

By using the join() function of the Thread class, we can easily achieve thread synchronization. It can ensure that threads execute in the order we specify, or wait for other threads to finish executing before continuing. This is very useful for some scenarios that require cooperation between threads, such as waiting in the main thread for all sub-threads to finish executing before processing the results.

It should be noted that an InterruptedException may be thrown when calling the join() function. We need to handle it in the code to avoid exceptions that cause program interruption.

Summary: Through the join() function of the Thread class, we can achieve thread synchronization and wait for other threads to complete execution before continuing. This is very useful in multi-threaded programming, which can ensure that threads execute in the order we specify, or wait for other threads to finish executing before continuing. It should be noted that InterruptedException may be thrown when calling the join() function, and we need to handle it.

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