• JDK并发包


    JDK并发包

    1. ReentrantLock(重入锁)

    public class ReenterLock implements Runnable
    {
        public static ReentrantLock lock = new ReentrantLock();
        public static int i = 0;
    
        @Override
        public void run(){
            for(int j = 0; j < 10000000; j++){
                lock.lock();
                try{
                    i++;
                }finally{
                    lock.unlock();
                }
            }
        }
    
        public static void main(String[] args){
            ReenterLock t1 = new ReenterLock();
            Thread t1 = new Thread(t1);
            Thread t2 = new Thread(t1);
            t1.start();t2.start();
            t1.join();t2.join();
         //i=20000000,说明i++被加锁,不能被同一线程同时访问 System.out.println(i); } }

    特性:

    1.1 中断响应

    package com.tianmaying.crawler.impl;
    
    import java.util.concurrent.locks.ReentrantLock;
    
    public class IntLock implements Runnable{
        public static ReentrantLock lock1 = new ReentrantLock();
        public static ReentrantLock lock2 = new ReentrantLock();
        int lock;
        public IntLock(int lock){
            this.lock = lock;
        }
    
        @Override
        public void run() {
            try {
                if (lock == 1) {
                    lock1.lockInterruptibly();
                    Thread.sleep(500);
                    lock2.lockInterruptibly();
                }else {
                    lock2.lockInterruptibly();
                    Thread.sleep(500);
                    lock1.lockInterruptibly();
                }
            } catch (InterruptedException e) {
                e.printStackTrace();
            }finally {
                if(lock1.isHeldByCurrentThread()){
                    lock1.unlock();
                }
                if(lock2.isHeldByCurrentThread()){
                    lock2.unlock();
                }
                System.out.println(Thread.currentThread().getId()+":线程退出。");
            }
        }
    
        public static void main(String[] args) throws InterruptedException {
            IntLock r1 = new IntLock(1);
            IntLock r2 = new IntLock(2);
            Thread t1 = new Thread(r1);
            Thread t2 = new Thread(r2);
            t1.start();
            t2.start();
            Thread.sleep(1000);
            t2.interrupt();
        }
    }

    1.2 可以为锁设置等待时间

    import java.util.concurrent.TimeUnit;
    import java.util.concurrent.locks.ReentrantLock;
    
    public class TimeLock implements Runnable{
        public static ReentrantLock lock = new ReentrantLock();
    
        @Override
        public void run() {
            try {
                if(lock.tryLock(5, TimeUnit.SECONDS)){
                    System.out.println("get lock success");
                    Thread.sleep(6000);
                }else{
                    System.out.println("get lock failed");
                }
            } catch (InterruptedException e) {
                e.printStackTrace();
            }finally {
                if(lock.isHeldByCurrentThread()){
                    lock.unlock();
                }
            }
        }
    
        public static void main(String[] args){
            TimeLock t1 = new TimeLock();
            Thread t11 = new Thread(t1);
            Thread t12 = new Thread(t1);
            t11.start();
            t12.start();
        }
    }

    第一个线程获得了锁,然后休眠6s,然后第二个线程申请锁,等待5s,锁仍然在第一个线程手上,然后第二线程会输出获取锁失败。

     使用tryLock()锁,会不断尝试,总会拿到自己的资源

    import java.util.concurrent.locks.ReentrantLock;
    
    public class TryLock implements Runnable{
        public static ReentrantLock lock1 = new ReentrantLock();
        public static ReentrantLock lock2 = new ReentrantLock();
        int lock;
    
        public TryLock(int lock){
            this.lock = lock;
        }
    
        @Override
        public void run() {
            if(lock == 1){
                while(true){
                    if(lock1.tryLock()){
                        try {
                            try {
                                Thread.sleep(500);
                            } catch (InterruptedException e) {
                                e.printStackTrace();
                            }
                            if (lock2.tryLock()) {
                                try {
                                    System.out.println(Thread.currentThread().getId() + ":My Job done");
                                    return;
                                } finally {
                                    lock2.unlock();
                                }
                            }
                        }finally {
                            lock1.unlock();
                        }
                    }
                }
            }else{
                while(true){
                    if(lock2.tryLock()){
                        try {
                            try {
                                Thread.sleep(500);
                            } catch (InterruptedException e) {
                                e.printStackTrace();
                            }
                            if (lock1.tryLock()) {
                                try {
                                    System.out.println(Thread.currentThread().getId() + ":My Job done");
                                    return;
                                } finally {
                                    lock1.unlock();
                                }
                            }
                        }finally {
                            lock2.unlock();
                        }
                    }
                }
            }
        }
    
        public static void main(String[] args){
            TryLock r1 = new TryLock(1);
            TryLock r2 = new TryLock(2);
            Thread t1 = new Thread(r1);
            Thread t2 = new Thread(r2);
            t1.start();
            t2.start();
        }
    }

    可以设置ReentrantLock为公平锁,ReentrantLock fairLock = new ReentrantLock(true);

    import java.util.concurrent.locks.ReentrantLock;
    
    public class FairLock implements Runnable{
        public static ReentrantLock fairLock = new ReentrantLock(true);
    
        @Override
        public void run() {
            while(true){
                try {
                    fairLock.lock();
                    System.out.println(Thread.currentThread().getName() + "获得锁");
                }finally {
                    fairLock.unlock();
                }
            }
        }
    
        public static void main(String[] args){
            FairLock r1 = new FairLock();
            Thread t1 = new Thread(r1,"Thread_t1");
            Thread t2 = new Thread(r1,"Thread_t2");
            t1.start();
            t2.start();
        }
    }

    输出的结果:

    可以看出来线程1和线程2交替获得锁,很公平

    可以看出来线程1和线程2并不是很公平的获得锁

    public class ReentrantLockCondition implements Runnable{
        public static ReentrantLock lock = new ReentrantLock();
        public static Condition condition = lock.newCondition();
        @Override
        public void run() {
            try {
                lock.lock();
                condition.await();
                System.out.println("Thread is going on");
            } catch (InterruptedException e) {
                e.printStackTrace();
            }finally {
                lock.unlock();
            }
        }
    
        public static void main(String[] args) throws InterruptedException {
            ReentrantLockCondition r1 = new ReentrantLockCondition();
            Thread t1 = new Thread(r1);
            t1.start();
            Thread.sleep(2000);
            lock.lock();
            condition.signal();
            lock.unlock();
        }
    }
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  • 原文地址:https://www.cnblogs.com/zhangchiblog/p/8888871.html
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