Java使用重入锁实现线程同步的示例代码

void safeIncrement() { lock.lock(); try { /* 更新共享计数 */ } finally { lock.unlock(); } }
boolean trySafeIncrement(long timeout, TimeUnit unit) { if (lock.tryLock(timeout, unit)) { try { ... } finally { lock.unlock(); } } else { /* 超时逻辑 */ } }
void interruptibleAccess() throws InterruptedException { lock.lockInterruptibly(); try { ... } finally { lock.unlock(); } }

/*
 * =====================================================
 * File: SharedResource.java
 * 共享资源类，使用 ReentrantLock 实现多种同步策略
 * =====================================================
 */
package com.example.lock;

import java.util.concurrent.TimeUnit;
import java.util.concurrent.locks.Condition;
import java.util.concurrent.locks.ReentrantLock;

public class SharedResource {
    private int counter = 0;
    private final ReentrantLock lock;
    private final Condition notZero;

    /**
     * 构造函数：可指定是否公平锁
     */
    public SharedResource(boolean fair) {
        this.lock = new ReentrantLock(fair);
        this.notZero = lock.newCondition();
    }

    /**
     * 基本互斥：安全地递增 counter
     */
    public void safeIncrement() {
        lock.lock();
        try {
            counter++;
            System.out.printf("%s incremented to %d%n",
                Thread.currentThread().getName(), counter);
            notZero.signalAll();
        } finally {
            lock.unlock();
        }
    }

    /**
     * 带超时尝试获取锁的递增
     */
    public boolean trySafeIncrement(long timeout, TimeUnit unit) {
        boolean acquired = false;
        try {
            acquired = lock.tryLock(timeout, unit);
            if (acquired) {
                counter++;
                System.out.printf("%s timed increment to %d%n",
                    Thread.currentThread().getName(), counter);
                notZero.signalAll();
                return true;
            } else {
                System.out.printf("%s failed to acquire lock in %d %s%n",
                    Thread.currentThread().getName(), timeout, unit);
                return false;
            }
        } catch (InterruptedException e) {
            Thread.currentThread().interrupt();
            System.out.printf("%s interrupted while waiting%n",
                Thread.currentThread().getName());
            return false;
        } finally {
            if (acquired) lock.unlock();
        }
    }

    /**
     * 可中断地获取锁并等待 counter > 0 后消费
     */
    public int interruptibleConsume() throws InterruptedException {
        lock.lockInterruptibly();
        try {
            while (counter == 0) {
                System.out.printf("%s waiting for counter > 0%n",
                    Thread.currentThread().getName());
                notZero.await();
            }
            counter--;
            System.out.printf("%s consumed to %d%n",
                Thread.currentThread().getName(), counter);
            return counter;
        } finally {
            lock.unlock();
        }
    }

    /**
     * 监控方法：打印当前锁状态
     */
    public void printLockStatus() {
        System.out.printf("Lock held by thread: %s, holdCount=%d, queuedThreads=%d%n",
            lock.isLocked() && lock.isHeldByCurrentThread()
                ? Thread.currentThread().getName()
                : "other",
            lock.getHoldCount(),
            lock.getQueueLength());
    }
}


/*
 * =====================================================
 * File: LockDemo.java
 * 演示：多线程调用 SharedResource 不同方法
 * =====================================================
 */
package com.example.lock;

import java.util.concurrent.*;
import java.util.concurrent.atomic.AtomicInteger;

public class LockDemo {
    public static void main(String[] args) throws InterruptedException {
        SharedResource fairResource = new SharedResource(true);
        SharedResource unfairResource = new SharedResource(false);

        ExecutorService exec = Executors.newFixedThreadPool(6);
        CountDownLatch startLatch = new CountDownLatch(1);
        AtomicInteger successCount = new AtomicInteger(0);
        AtomicInteger failCount = new AtomicInteger(0);

        // 创建 2 个常规增量任务
        for (int i = 0; i < 2; i++) {
            exec.submit(() -> {
                await(startLatch);
                fairResource.safeIncrement();
            });
        }

        // 创建 2 个带超时尝试锁任务
        for (int i = 0; i < 2; i++) {
            exec.submit(() -> {
                await(startLatch);
                if (fairResource.trySafeIncrement(500, TimeUnit.MILLISECONDS)) {
                    successCount.incrementAndGet();
                } else {
                    failCount.incrementAndGet();
                }
            });
        }

        // 创建 2 个可中断消费任务
        for (int i = 0; i < 2; i++) {
            exec.submit(() -> {
                await(startLatch);
                try {
                    unfairResource.interruptibleConsume();
                } catch (InterruptedException e) {
                    System.out.printf("%s interrupted%n",
                        Thread.currentThread().getName());
                }
            });
        }

        // 启动所有任务
        startLatch.countDown();

        // 等待一段时间后中断消费任务
        Thread.sleep(1000);
        exec.shutdownNow();
        exec.awaitTermination(5, TimeUnit.SECONDS);

        System.out.printf("TryLock successes: %d, failures: %d%n",
            successCount.get(), failCount.get());
    }

    private static void await(CountDownLatch latch) {
        try {
            latch.await();
        } catch (InterruptedException ignored) {}
    }
}