java 中Lock的使用

2019独角兽企业重金招聘Python工程师标准>>>

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;}@Overridepublic 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;}@Overridepublic void run() {service.methodA();}
}class ThreadB extends Thread {private MyService service;ThreadB(MyService service) {this.service = service;}@Overridepublic 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;}@Overridepublic void run() {service.methodA();}
}class ThreadB extends Thread {private MyService service;ThreadB(MyService service) {this.service = service;}@Overridepublic 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

转载于:https://my.oschina.net/u/1177694/blog/1635168