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();
    }
}