Java~多线程ReentrantLock类常用的十四个方法, 使用Condition实现多线程的顺序执行

程序员文章站 2022-05-03 20:57:38

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文章目录

方法getHoldCount()

该方法的作用是查询当前被这个锁锁定的线程个数, 也就是这个锁执行lock的次数

public class Demo1 {

    public static void main(String[] args) {
        ReentrantLock reentrantLock = new ReentrantLock();
        Thread thread = new Thread() {
            @Override
            public void run() {
                method1();
            }

            public void method1() {
                reentrantLock.lock();
                System.out.println(Thread.currentThread().getName() + " " +
                        reentrantLock.getHoldCount());
                method2();
                reentrantLock.unlock();
            }

            public void method2() {
                reentrantLock.lock();
                System.out.println(Thread.currentThread().getName() + " " +
                        reentrantLock.getHoldCount());
                reentrantLock.unlock();
            }
        };
        thread.start();
    }
}

Java~多线程ReentrantLock类常用的十四个方法, 使用Condition实现多线程的顺序执行

方法getQueueLength()

该方法返回的是想要获取这个锁的线程个数
比如有5个线程，1个线程首先执行await()方法，那么在调用getQueueLength()方法后返回值是4，说明有4个线程同时在等待lock 的释放。

public class Demo2 {

    public static void main(String[] args) throws InterruptedException {
        ReentrantLock reentrantLock = new ReentrantLock();
        Runnable runnable = new Runnable() {
            @Override
            public void run() {
                reentrantLock.lock();
                try {
                    Thread.sleep(Integer.MAX_VALUE);
                } catch (InterruptedException e) {
                    e.printStackTrace();
                } finally {
                    reentrantLock.unlock();
                }
            }
        };
        Thread[] threads = new Thread[5];
        for (int i = 0; i < 5; i++) {
            threads[i] = new Thread(runnable);
        }
        for (int i = 0; i < 5; i++) {
            threads[i].start();
        }
        Thread.sleep(100);
        System.out.println(reentrantLock.getQueueLength());
    }
}

Java~多线程ReentrantLock类常用的十四个方法, 使用Condition实现多线程的顺序执行

方法getWaitQueueLength()

方法int getWaitfQueueI engh(Condition condition)的作用是返回等待与此锁定相关的给定条件Condition的线程估计数，比如有5个线程，每个线程都执行了同一个condition对象的await()方法，则调用getWaitQueueLengh(Condition condition)方法时返回的int值是5。
也就是同一个condition执行await的次数, 也就是目前有多少个线程处于某一个condition的await下

public class Demo3 {

    public static void main(String[] args) {
        ReentrantLock reentrantLock = new ReentrantLock();
        Condition condition = reentrantLock.newCondition();
        Runnable runnable = new Runnable() {
            @Override
            public void run() {
                reentrantLock.lock();
                try {
                    System.out.println(reentrantLock.getWaitQueueLength(condition));
                    condition.await();
                } catch (InterruptedException e) {
                    e.printStackTrace();
                }
            }
        };
        Thread[] threads = new Thread[5];
        for (int i = 0; i < 5; i++) {
            threads[i] = new Thread(runnable);
        }
        for (int i = 0; i < 5; i++) {
            threads[i].start();
        }

    }
}

Java~多线程ReentrantLock类常用的十四个方法, 使用Condition实现多线程的顺序执行

方法hasQueuedThread()和方法hasQueuedThreads()

方法boolean hasQueuedThread(Thread thread) 的作用是查询指定的线程是否正在等待获取此锁定。也就是查看指定线程想要获取锁.
方法boolean hasQueuedThreads()的作用是查询是否有线程正在等待获取此锁定。也就是这个不指定了, 而是只要有想要这把锁的就返回true

public class Demo4 {

    public static void main(String[] args) throws InterruptedException {
        ReentrantLock reentrantLock = new ReentrantLock();
        Runnable runnable = new Runnable() {
            @Override
            public void run() {
                reentrantLock.lock();
                try {
                    Thread.sleep(Integer.MAX_VALUE);
                } catch (InterruptedException e) {
                    e.printStackTrace();
                } finally {
                    reentrantLock.unlock();
                }
            }
        };
        Thread a = new Thread(runnable);
        a.start();
        Thread.sleep(100);
        Thread b = new Thread(runnable);
        b.start();
        Thread.sleep(100);
        System.out.println("a需要吗? " + reentrantLock.hasQueuedThread(a));
        System.out.println("b需要吗? " + reentrantLock.hasQueuedThread(b));
        System.out.println("有需要吗? " + reentrantLock.hasQueuedThreads());
    }
}

Java~多线程ReentrantLock类常用的十四个方法, 使用Condition实现多线程的顺序执行

方法hasWaiters()

方法boolean hasWaiters(Condition condition)的作用是查询是否有线程正在等待与此锁定有关的condition条件。
也就是在这个condition下有没有线程执行了await还没有唤醒
这个方法必须在加锁的情况下使用不然没有对象监视器的所有权, 从而抛出IllegalMonitorStateException

public class Demo5 {

    public static void main(String[] args) throws InterruptedException {
        ReentrantLock reentrantLock = new ReentrantLock();
        Condition condition = reentrantLock.newCondition();
        Thread thread = new Thread() {
            @Override
            public void run() {
                reentrantLock.lock();
                try {
                    condition.await();
                } catch (InterruptedException e) {
                    e.printStackTrace();
                } finally {
                    reentrantLock.unlock();
                }
            }
        };

        thread.start();
        Thread.sleep(100);
        //注意使用这个方法必须在lock下使用, 不然会没有这个对象监视器的所有权而抛出异常
        reentrantLock.lock();
        System.out.println("有没有等待signal的线程 " + reentrantLock.hasWaiters(condition));
        reentrantLock.unlock();
    }
}

Java~多线程ReentrantLock类常用的十四个方法, 使用Condition实现多线程的顺序执行

方法isFair()

方法boolean isFair()的作用是判断是不是公平锁。这个很简单就不做演示了

方法isHeldByCurrentThread()

方法boolean isHeldByCurrentThread()的作用是查询当前线程是否保持此锁定。
也就是这个线程是否执行了lock

public class Demo6 {

    public static void main(String[] args) {
        ReentrantLock reentrantLock = new ReentrantLock();
        System.out.println(reentrantLock.isHeldByCurrentThread());
        reentrantLock.lock();
        System.out.println(reentrantLock.isHeldByCurrentThread());
        reentrantLock.unlock();
    }
}

Java~多线程ReentrantLock类常用的十四个方法, 使用Condition实现多线程的顺序执行

方法isLocked()

方法boolean isLocked()的作用是查询此锁定是否由任意线程保持。
也就是这把锁是否已经执行了lock

public class Demo7 {

    public static void main(String[] args) throws InterruptedException {
        ReentrantLock reentrantLock = new ReentrantLock();
        System.out.println(reentrantLock.isLocked());

        Thread thread = new Thread() {
            @Override
            public void run() {
                reentrantLock.lock();
                System.out.println("执行lock");
                try {
                    Thread.sleep(1000);
                } catch (InterruptedException e) {
                    e.printStackTrace();
                } finally {
                    System.out.println("释放lock");
                    reentrantLock.unlock();
                }
            }
        };
        thread.start();
        for (int i = 0; i < 10; i++) {
            System.out.println(reentrantLock.isLocked());
            Thread.sleep(200);
        }


    }
}

Java~多线程ReentrantLock类常用的十四个方法, 使用Condition实现多线程的顺序执行

方法lockInterruptibly()、tryLock()和tryLock(long timeout,TimeUnit unit)

这三个方法大同小异
方法void locklnterruptibly()的作用是:如果当前线程未被中断，则获取锁定，如果已经被中断则出现异常。也就是我们在普通使用lock方法加锁时, 如果这个线程被中断了是不会抛出异常的, 而使用locklnterruptibly方法加锁如果这个线程中断了是会抛出异常的
方法boolean tryLock()的作用是，仅在调用时锁定未被另一个线程保持的情况下，才获取该锁定。本意就是我尝试去获取锁, 如果没人拿我就拿, 如果有人拿我就不要这把锁了
方法boolean tryLock(long timeout, TimeUnit unit)的作用是，如果锁定在给定等待时间内没有被另一个线程保持，且当前线程未被中断，则获取该锁定。也就是我会支持一段时间去尝试那这个把锁, 在这个时间段里, 我没拿到我就不要了

public class Service1 {

    private ReentrantLock reentrantLock = new ReentrantLock();

    public void method() {
        try {
            if (reentrantLock.tryLock(3, TimeUnit.SECONDS)) {
                System.out.println(Thread.currentThread().getName() + " " +
                        "获取锁的时间:" + System.currentTimeMillis());
                Thread.sleep(10000);
            } else {
                System.out.println(Thread.currentThread().getName() + " 没有获得锁");
            }
        } catch (InterruptedException e) {
            e.printStackTrace();
        } finally {
            if (reentrantLock.isHeldByCurrentThread()) {
                reentrantLock.unlock();
            }
        }
    }
}

public class Demo1 {

    public static void main(String[] args) throws InterruptedException {
        Service1 service1 = new Service1();
        Runnable runnable = new Runnable() {
            @Override
            public void run() {
                System.out.println(Thread.currentThread().getName() + " 执行method时间" +
                        System.currentTimeMillis());
                service1.method();
            }
        };
        Thread a = new Thread(runnable, "A");
        a.start();
        Thread b = new Thread(runnable, "B");
        b.start();
    }
}

Java~多线程ReentrantLock类常用的十四个方法, 使用Condition实现多线程的顺序执行

方法awaitUninterruptibly()

我没在普通使用await的时候, 如果这个线程中断了, 就会抛出异常, 但是使用awaitUninterruptibly()即使在等待中的线程被打断了, 也不会抛出异常

方法await(time) 和 awaitUntil()

这俩个方法和synchronized的wait(long)和相似, 就是wait等待一段时间, 可以提前唤醒, 也可以等时间到了自动唤醒.

public class Demo2 {

    public static void main(String[] args) throws InterruptedException {
        ReentrantLock reentrantLock = new ReentrantLock();
        Condition condition = reentrantLock.newCondition();

        reentrantLock.lock();
        System.out.println(Thread.currentThread().getName() + " 开始时间:" +
                System.currentTimeMillis());
        condition.await(3, TimeUnit.SECONDS);
        System.out.println(Thread.currentThread().getName() + " 结束时间:" +
                System.currentTimeMillis());
        reentrantLock.unlock();


    }
}

Java~多线程ReentrantLock类常用的十四个方法, 使用Condition实现多线程的顺序执行

使用Condition实现多线程的顺序执行

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

/**
 * Created with IntelliJ IDEA.
 * Description: If you don't work hard, you will a loser.
 * User: Listen-Y.
 * Date: 2020-10-10
 * Time: 18:25
 */
public class Run {

    private static ReentrantLock reentrantLock = new ReentrantLock();
    //关键变量
    volatile private static int key = 1;
    //三个condition保证三种线程 挨个运行
    private static Condition conditionA = reentrantLock.newCondition();
    private static Condition conditionB = reentrantLock.newCondition();
    private static Condition conditionC = reentrantLock.newCondition();

    public static void main(String[] args) {
        //实现三个runnable任务
        Runnable runnableA = new Runnable() {
            @Override
            public void run() {
                try {
                    reentrantLock.lock();
                    while (key != 1) {
                        conditionA.await();
                    }
                    for (int i = 0; i < 3; i++) {
                        System.out.println(Thread.currentThread().getName() + " " + i);
                    }
                    key = 2;
                    //唤醒所有B线程
                    conditionB.signalAll();
                } catch (InterruptedException e) {
                    e.printStackTrace();
                } finally {
                    reentrantLock.unlock();
                }
            }
        };
        Runnable runnableB = new Runnable() {
            @Override
            public void run() {
                try {
                    reentrantLock.lock();
                    while (key != 2) {
                        conditionB.await();
                    }
                    for (int i = 0; i < 3; i++) {
                        System.out.println(Thread.currentThread().getName() + " " + i);
                    }
                    key = 3;
                    //唤醒所有C线程
                    conditionC.signalAll();
                } catch (InterruptedException e) {
                    e.printStackTrace();
                } finally {
                    reentrantLock.unlock();
                }
            }
        };
        Runnable runnableC = new Runnable() {
            @Override
            public void run() {
                try {
                    reentrantLock.lock();
                    while (key != 3) {
                        conditionC.await();
                    }
                    for (int i = 0; i < 3; i++) {
                        System.out.println(Thread.currentThread().getName() + " " + i);
                    }
                    key = 1;
                    //唤醒所有A线程
                    conditionA.signalAll();
                } catch (InterruptedException e) {
                    e.printStackTrace();
                } finally {
                    reentrantLock.unlock();
                }
            }
        };

        //创建多个线程
        Thread[] threadsA = new Thread[5];
        Thread[] threadsB = new Thread[5];
        Thread[] threadsC = new Thread[5];
        for (int i = 0; i < 5; i++) {
            threadsA[i] = new Thread(runnableA, "ThreadA");
            threadsB[i] = new Thread(runnableB, "ThreadB");
            threadsC[i] = new Thread(runnableC, "ThreadC");
        }
        //启动所有线程
        for (int i = 0; i < 5; i++) {
            threadsA[i].start();
            threadsB[i].start();
            threadsC[i].start();
        }
    }
}

Java~多线程ReentrantLock类常用的十四个方法, 使用Condition实现多线程的顺序执行

相关标签：多线程 java 并发编程 thread

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