ReentrantLock可重入锁原理与实现解析

import java.util.concurrent.locks.ReentrantLock;

public class Counter {
    private int count = 0;
    private final ReentrantLock lock = new ReentrantLock();

    public void increment() {
        lock.lock();  // 获取锁
        try {
            count++;
        } finally {
            lock.unlock();  // 释放锁
        }
    }

    public int getCount() {
        lock.lock();
        try {
            return count;
        } finally {
            lock.unlock();
        }
    }
}

public void methodA() {
    lock.lock();
    try {
        System.out.println("methodA");
        methodB();  // 同一线程再次进入加锁方法
    } finally {
        lock.unlock();
    }
}

public void methodB() {
    lock.lock();
    try {
        System.out.println("methodB");
    } finally {
        lock.unlock();
    }
}

public boolean timedIncrement() {
    boolean acquired = lock.tryLock();  // 立即返回是否获取成功
    if (acquired) {
        try {
            count++;
            return true;
        } finally {
            lock.unlock();
        }
    }
    return false;  // 获取失败
}

boolean acquired = lock.tryLock(1, TimeUnit.SECONDS);

private final ReentrantLock fairLock = new ReentrantLock(true);  // 公平锁