Identification and avoidance of deadlock in Java parallel programming

Deadlock is a phenomenon that occurs in concurrent systems where multiple threads wait indefinitely for each other to release locks, causing the system to stall. Java provides ThreadMXBean and DeadlockMonitor classes to identify deadlocks. Best practices for avoiding deadlocks include: ordering locks, setting timeouts, detecting deadlocks periodically, using active waits, and minimizing lock granularity.

Deadlock identification and avoidance in Java parallel programming

Deadlock overview

Deadlock is a situation in a concurrent system where multiple threads wait indefinitely for each other to release locks, causing the system to stall.

Identifying deadlocks

Java provides the ThreadMXBean and DeadlockMonitor classes to detect deadlocks. ThreadMXBean allows you to obtain the status of a deadlocked thread, while DeadlockMonitor throws a DeadlockException when a deadlock is detected.

Practical case: deadlock example

Consider the following deadlock example:

Object lock1 = new Object();
Object lock2 = new Object();

Thread thread1 = new Thread(() -> {
    synchronized (lock1) {
        try {
            Thread.sleep(1000); // 线程 1 首先获取 lock1，然后休眠
        } catch (InterruptedException e) {
            e.printStackTrace();
        }
        synchronized (lock2) {
            // 线程 1 等待线程 2 释放 lock2，但线程 2 永远不会释放它
        }
    }
});

Thread thread2 = new Thread(() -> {
    synchronized (lock2) {
        try {
            Thread.sleep(1000); // 线程 2 首先获取 lock2，然后休眠
        } catch (InterruptedException e) {
            e.printStackTrace();
        }
        synchronized (lock1) {
            // 线程 2 等待线程 1 释放 lock1，但线程 1 永远不会释放它
        }
    }
});

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

Avoid deadlock

In order to avoid deadlocks, there are some best practices as follows:

• The order of acquiring locks: Define a lock order for all shared resources and always acquire them in that order Lock.
• Timeout mechanism: Set a timeout for the lock acquisition operation to avoid waiting indefinitely.
• Deadlock detection: Use the DeadlockMonitor class to detect deadlocks periodically.
• Active waiting: Let the thread waiting for the lock frequently check the status of the lock instead of blocking completely.
• Lock granularity minimization: Only lock the smallest block of code that needs to be locked to reduce the possibility of deadlock.

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