如何正确使用java的join()避免死锁-乐工具技术知识

在Java中，join()方法用于等待线程执行完成。如果不正确地使用join()方法，可能会导致死锁。为了避免死锁，可以遵循以下原则：

始终按照固定的顺序获取锁：如果多个线程需要访问共享资源，确保它们按照相同的顺序获取锁。这样可以避免循环等待的情况，从而避免死锁。

class DeadlockAvoidance {
    private final Object lock1 = new Object();
    private final Object lock2 = new Object();

    public void method1() {
        synchronized (lock1) {
            System.out.println("Thread 1: Holding lock1...");
            try { Thread.sleep(100); } catch (InterruptedException e) {}
            synchronized (lock2) {
                System.out.println("Thread 1: Holding lock1 and lock2...");
            }
        }
    }

    public void method2() {
        synchronized (lock1) {
            System.out.println("Thread 2: Holding lock1...");
            try { Thread.sleep(100); } catch (InterruptedException e) {}
            synchronized (lock2) {
                System.out.println("Thread 2: Holding lock1 and lock2...");
            }
        }
    }
}

使用超时机制：在调用join()方法时，可以设置一个超时时间。这样，如果线程在指定的时间内无法完成执行，它将放弃等待并继续执行其他任务。这可以降低死锁的风险。

Thread thread1 = new Thread(() -> {
    try {
        System.out.println("Thread 1: Waiting for thread2 to finish...");
        thread2.join(500); // 设置500毫秒的超时时间
        if (thread2.isAlive()) {
            System.out.println("Thread 1: Timeout occurred, continue executing...");
        } else {
            System.out.println("Thread 1: Thread2 finished, continue executing...");
        }
    } catch (InterruptedException e) {
        e.printStackTrace();
    }
});

Thread thread2 = new Thread(() -> {
    try {
        System.out.println("Thread 2: Waiting for thread1 to finish...");
        thread1.join(500); // 设置500毫秒的超时时间
        if (thread1.isAlive()) {
            System.out.println("Thread 2: Timeout occurred, continue executing...");
        } else {
            System.out.println("Thread 2: Thread1 finished, continue executing...");
        }
    } catch (InterruptedException e) {
        e.printStackTrace();
    }
});

thread1.start();
thread2.start();