java 中Lock的使用【轉】

ReentrantLock也能夠讓代碼塊原子執(zhí)行，但是比synchronized更加強大，ReentrantLock具有嗅探鎖定、多路分支通知等功能。
嗅探鎖定：是指獲取鎖時如果鎖已經被其他線程獲取到ReentrantLock可以進行指定等待時間獲取鎖或者
多路分支通知：是指線程發(fā)生await時，線程可以選擇注冊在不同的監(jiān)視器Condition對象上，在適當的時候可以選擇指定的監(jiān)視器Condition對象上的線程進行signal通知、執(zhí)行
1、多線程執(zhí)行同一代碼塊互斥

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();
    }
}

結果

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、多線程執(zhí)行不同代碼塊互斥

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();
    }
}

結果：

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

當多線程進入await狀態(tài)時，利用Condition監(jiān)視器對不同類型線程通知

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();
    }
}

測試結果1：

MethodA begin ThreadName=A 1476800025028
MethodB begin ThreadName=B 1476800025029
MethodA end ThreadName=A 1476800026028
MethodB end ThreadName=B 1476800027028

修改代碼為：

 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();
    }

結果為：

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、公平所與非公平鎖
公平鎖是指線程獲（getting）取鎖的順序和線程鎖定（got）的順序相同，

Lock的一些方法說明
A） getHoldCount()
獲取當前鎖定（got）的個數
B）getQueueLength()
獲取當前正在等待獲取（getting）鎖的線程數（Threads）
C）getWaitQueueLength(Condition)
返回等待（await）與此鎖定（got）的Condition相關的個數

原文：https://blog.csdn.net/jihaitaowangyi/article/details/52852693

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