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java 中Lock的使用

發布時間：2024/4/14 编程问答 40 豆豆

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ReentrantLock也能夠讓代碼塊原子執行，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：是指線程發生await時，線程可以選擇注冊在不同的監視器Condition對象上，在適當的時候可以選擇指定的監視器Condition對象上的線程進行signal通知、執行

1、多線程執行同一代碼塊互斥

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;}@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();} }

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;}@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();} }

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狀態時，利用Condition監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;}@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();} }

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

轉載于:https://my.oschina.net/u/1177694/blog/1635168

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