Java多线程--Lock的使用

亦凉 2022-05-24 03:20 268阅读 0赞

（转自：[https://blog.csdn.net/jihaitaowangyi/article/details/52852693][https_blog.csdn.net_jihaitaowangyi_article_details_52852693] 侵删）

ReentrantLock也能够让代码块原子执行，但是比synchronized更加强大，ReentrantLock具有嗅探锁定、多路分支通知等功能。   
嗅探锁定：是指获取锁时如果锁已经被其他线程获取到ReentrantLock可以进行指定等待时间获取锁或者   
多路分支通知：是指线程发生await时，线程可以选择注册在不同的监视器Condition对象上，在适当的时候可以选择指定的监视器Condition对象上的线程进行signal通知、执行

## 1、多线程执行同一代码块互斥 ##

import java.util.concurrent.locks.ReentrantLock;
    
    class MyService {
    
        private ReentrantLock lock = new ReentrantLock();
    
        public void method() {
            try {
                lock.lock();
                for (int i = 1; i <= 3; i++) {
                    Thread.sleep(1000);
                    System.out.println("ThreadName=" + Thread.currentThread().getName() + " " + i);
                }
            } catch (InterruptedException e) {
                e.printStackTrace();
            }finally {
                lock.unlock();
            }
        }
    }
    
    class MyThread extends Thread {
    
        private MyService service;
    
        MyThread(MyService service) {
            this.service = service;
        }
    
        @Override
        public void run() {
            service.method();
        }
    }
    
    public class Test {
    
        public static void main(String[] args) {
            MyService service = new MyService();
            MyThread myThread1 = new MyThread(service);
            MyThread myThread2 = new MyThread(service);
    
            myThread1.start();
            myThread2.start();
        }
    }

结果   
ThreadName=Thread-0 1   
ThreadName=Thread-0 2   
ThreadName=Thread-0 3   
ThreadName=Thread-1 1   
ThreadName=Thread-1 2   
ThreadName=Thread-1 3

## 2、多线程执行不同代码块互斥 ##

import java.util.concurrent.locks.ReentrantLock;
    
    class MyService {
        private ReentrantLock lock = new ReentrantLock();
    
        public void methodA() {
            lock.lock();
            try {
                System.out.println("MethodA begin ThreadName=" + Thread.currentThread().getName());
                for (int i = 1; i <= 3; i++) {
                    System.out.println("ThreadName=" + Thread.currentThread().getName() + " " + i);
                    Thread.sleep(1000);
                }
                System.out.println("MethodA end ThreadName=" + Thread.currentThread().getName());
            } catch (InterruptedException e) {
                e.printStackTrace();
            } finally {
                lock.unlock();
            }
        }
    
        public void methodB() {
            lock.lock();
            try {
                System.out.println("MethodB begin ThreadName=" + Thread.currentThread().getName());
                for (int i = 1; i <= 3; i++) {
                    System.out.println("ThreadName=" + Thread.currentThread().getName() + " " + i);
                    Thread.sleep(1000);
                }
                System.out.println("MethodB end ThreadName=" + Thread.currentThread().getName());
            } catch (InterruptedException e) {
                e.printStackTrace();
            } finally {
                lock.unlock();
            }
        }
    }
    
    class ThreadA extends Thread {
    
        private MyService service;
    
        ThreadA(MyService service) {
            this.service = service;
        }
    
        @Override
        public void run() {
            service.methodA();
        }
    }
    
    class ThreadB extends Thread {
    
        private MyService service;
    
        ThreadB(MyService service) {
            this.service = service;
        }
    
        @Override
        public void run() {
            service.methodB();
        }
    }
    
    public class Test {
    
        public static void main(String[] args) {
            MyService service = new MyService();
            ThreadA threadA = new ThreadA(service);
            threadA.setName("A");
    
            ThreadB threadB = new ThreadB(service);
            threadB.setName("B");
            threadA.start();
            threadB.start();
        }
    }

结果：   
MethodA begin ThreadName=A   
ThreadName=A 1   
ThreadName=A 2   
ThreadName=A 3   
MethodA end ThreadName=A   
MethodB begin ThreadName=B   
ThreadName=B 1   
ThreadName=B 2   
ThreadName=B 3   
MethodB end ThreadName=B

## 3、多路通知 ##

当多线程进入await状态时，利用Condition监视器对不同类型线程通知

import java.util.concurrent.locks.Condition;
    import java.util.concurrent.locks.ReentrantLock;
    
    class MyService {
        private ReentrantLock lock = new ReentrantLock();
        private Condition conditionA = lock.newCondition();
        private Condition conditionB = lock.newCondition();
    
        public void methodA() {
            lock.lock();
            try {
                System.out.println("MethodA begin ThreadName=" + Thread.currentThread().getName() + " " + System.currentTimeMillis());
                conditionA.await();
                System.out.println("MethodA end ThreadName=" + Thread.currentThread().getName() + " " + System.currentTimeMillis());
            } catch (InterruptedException e) {
                e.printStackTrace();
            } finally {
                lock.unlock();
            }
        }
    
        public void methodB() {
            lock.lock();
            try {
                System.out.println("MethodB begin ThreadName=" + Thread.currentThread().getName() + " " + System.currentTimeMillis());
                conditionB.await();
                System.out.println("MethodB end ThreadName=" + Thread.currentThread().getName() + " " + System.currentTimeMillis());
            } catch (InterruptedException e) {
                e.printStackTrace();
            } finally {
                lock.unlock();
            }
        }
    
        public void signalA() {
            lock.lock();
            conditionA.signal();
            lock.unlock();
        }
        public void signalA_All() {
            lock.lock();
            conditionA.signalAll();
            lock.unlock();
        }
    
    
        public void signalB() {
            lock.lock();
            conditionB.signal();
            lock.unlock();
        }
        public void signalB_All() {
            lock.lock();
            conditionB.signalAll();
            lock.unlock();
        }
    }
    
    class ThreadA extends Thread {
    
        private MyService service;
    
        ThreadA(MyService service) {
            this.service = service;
        }
    
        @Override
        public void run() {
            service.methodA();
        }
    }
    
    class ThreadB extends Thread {
    
        private MyService service;
    
        ThreadB(MyService service) {
            this.service = service;
        }
    
        @Override
        public void run() {
            service.methodB();
        }
    }
    
    public class Test {
    
        public static void main(String[] args) throws InterruptedException {
            MyService service = new MyService();
            ThreadA threadA = new ThreadA(service);
            threadA.setName("A");
    
            ThreadB threadB = new ThreadB(service);
            threadB.setName("B");
            threadA.start();
            threadB.start();
    
            Thread.sleep(1000);
            service.signalA();
            Thread.sleep(1000);
            service.signalB();
    
    // ThreadA[] threadAs = new ThreadA[10];
    // for (int i=0;i<5;i++){ 
    // threadAs[i] = new ThreadA(service);
    // }
    // ThreadB[] threadBs = new ThreadB[10];
    // for (int i=0;i<5;i++){ 
    // threadBs[i] = new ThreadB(service);
    // }
    //
    // for (int i=0;i<5;i++){ 
    // threadAs[i].start();
    // threadBs[i].start();
    // }
    //
    // Thread.sleep(1000);
    // service.signalA_All();
    // Thread.sleep(1000);
    // service.signalB_All();
        }
    }

测试结果1：   
MethodA begin ThreadName=A 1476800025028   
MethodB begin ThreadName=B 1476800025029   
MethodA end ThreadName=A 1476800026028   
MethodB end ThreadName=B 1476800027028

修改代码为：

public static void main(String[] args) throws InterruptedException {
            MyService service = new MyService();
    // ThreadA threadA = new ThreadA(service);
    // threadA.setName("A");
    //
    // ThreadB threadB = new ThreadB(service);
    // threadB.setName("B");
    // threadA.start();
    // threadB.start();
    //
    // Thread.sleep(1000);
    // service.signalA();
    // Thread.sleep(1000);
    // service.signalB();
    
            ThreadA[] threadAs = new ThreadA[10];
            for (int i=0;i<5;i++){
                threadAs[i] = new ThreadA(service);
            }
            ThreadB[] threadBs = new ThreadB[10];
            for (int i=0;i<5;i++){
                threadBs[i] = new ThreadB(service);
            }
    
            for (int i=0;i<5;i++){
                threadAs[i].start();
                threadBs[i].start();
            }
    
            Thread.sleep(1000);
            service.signalA_All();
            Thread.sleep(1000);
            service.signalB_All();
        }

结果为：   
MethodA begin ThreadName=Thread-0 1476800227416   
MethodB begin ThreadName=Thread-7 1476800227417   
MethodB begin ThreadName=Thread-5 1476800227417   
MethodA begin ThreadName=Thread-3 1476800227418   
MethodA begin ThreadName=Thread-1 1476800227418   
MethodA begin ThreadName=Thread-4 1476800227418   
MethodB begin ThreadName=Thread-6 1476800227418   
MethodA begin ThreadName=Thread-2 1476800227418   
MethodB begin ThreadName=Thread-8 1476800227418   
MethodB begin ThreadName=Thread-9 1476800227418   
MethodA end ThreadName=Thread-0 1476800228419   
MethodA end ThreadName=Thread-3 1476800228419   
MethodA end ThreadName=Thread-1 1476800228419   
MethodA end ThreadName=Thread-4 1476800228420   
MethodA end ThreadName=Thread-2 1476800228420   
MethodB end ThreadName=Thread-7 1476800229419   
MethodB end ThreadName=Thread-5 1476800229419   
MethodB end ThreadName=Thread-6 1476800229419   
MethodB end ThreadName=Thread-8 1476800229419   
MethodB end ThreadName=Thread-9 1476800229419

4、公平所与非公平锁   
公平锁是指线程获（getting）取锁的顺序和线程锁定（got）的顺序相同，

Lock的一些方法说明   
A） getHoldCount()   
获取当前锁定（got）的个数   
B）getQueueLength()   
获取当前正在等待获取（getting）锁的线程数（Threads）   
C）getWaitQueueLength(Condition)   
返回等待（await）与此锁定（got）的Condition相关的个数

[https_blog.csdn.net_jihaitaowangyi_article_details_52852693]: https://blog.csdn.net/jihaitaowangyi/article/details/52852693