本文主要是介绍ReentrantLock的三种获取锁Lock，tryLock，lockInterruptibly的区别，希望对大家解决编程问题提供一定的参考价值，需要的开发者们随着小编来一起学习吧！
重入锁有三种获取锁的方式,本文就是来说明三种方式的异同点的.
lock
public void lock()获得锁。
- 如果锁没有被另一个线程占用并且立即返回，则将锁定计数设置为1。
- 如果当前线程已经保持锁定，则保持计数增加1，该方法立即返回。
- 如果锁被另一个线程保持，则当前线程将被禁用以进行线程调度，并且在锁定已被获取之前处于休眠状态，此时锁定保持计数被设置为1。
tryLock
boolean tryLock();- 当获取锁时，只有当该锁资源没有被其他线程持有才可以获取到，并且返回true，同时设置持有count为1。
- 当获取锁时，当前线程已持有该锁，那么锁可用时，返回true，同时设置持有count加1。
- 当获取锁时，如果其他线程持有该锁，无可用锁资源，直接返回false，这时候线程不用阻塞等待，可以先去做其他事情。
- 即使该锁是公平锁fairLock，使用tryLock()的方式获取锁也会是非公平的方式，只要获取锁时该锁可用那么就会直接获取并返回true。这种直接插入的特性在一些特定场景是很有用的。但是如果就是想使用公平的方式的话，可以试一试tryLock(0,TimeUnit.SECONDS)，几乎跟公平锁没区别，只是会监测中断事件
使用标准模板:
Lock lock = ...;
if (lock.tryLock()) {try {// manipulate protected state} finally {lock.unlock();}} else {// perform alternative actions}tryLock的重载方法:
boolean tryLock(long time, TimeUnit unit) throws InterruptedException;
- 获取锁成功或者超时之后返回。而且在公平锁和非公平锁的场景下都可以使用，只是会增加对中断事件的监测。
- 当获取锁时，锁资源在超时时间之内变为可用，并且在等待时没有被中断，那么当前线程成功获取锁，返回true，同时当前线程持有锁的count设置为1.
- 当获取锁时，在超时时间之内没有锁资源可用，那么当前线程获取失败，不再继续等待，返回false.
- 当获取锁时，在超时等待时间之内，被中断了，那么抛出InterruptedException，不再继续等待.
- 当获取锁时，在超时时间之内锁可用，并且当前线程之前已持有该锁，那么成功获取锁，同时持有count加1.
lockInterruptibly
void lockInterruptibly() throws InterruptedException;- 当获取锁时，锁资源可用，那么当前线程成功获得锁，同时持有count设置为1，返回true.
- 当获取锁时，锁资源可用，当前线程已持有该锁，它成功获取该锁，同时持有count增加1，返回true.
- 当获取锁时，锁资源不可用，那么该线程开始阻塞休眠等待，但是等待过程中如果有中断事件，那么会停止等待，立即返回.
- 当获取锁时，锁资源不可用，线程开始阻塞休眠等待，如果等待过程中锁资源变为可用，那么当前线程成功获得锁，同时持有count设置为1，返回true.
lockInterruptibly()获取锁是以排他的模式获取，一旦被中断就放弃等待获取。在等待开始时首先检测中断状态，然后至少调用一次tryAcquire，成功获取就返回true。否则当前线程就开始排队，并且不断的被blocking、unblocking、invoking tryAcquire 直到获取成功或者被中断为止。
下面使用代码进行演示:
package com.springcloud.server.springserver.thread;import java.util.concurrent.locks.ReentrantLock;public class TestLockAndTryLock {private ReentrantLock rlock = new ReentrantLock();private void lockTest(){long currentTime = System.currentTimeMillis();try {rlock.lock();while (System.currentTimeMillis() - currentTime <= 1000){//assume do something}System.out.println("lockTest----current thread get the lock: " + Thread.currentThread().getName());}finally {rlock.unlock();System.out.println("lockTest----current thread release the lock: " + Thread.currentThread().getName());}}private void tryLockTest(){long currentTime = System.currentTimeMillis();while (System.currentTimeMillis() - currentTime <= 100){//assume do something}if (rlock.tryLock()){try {System.out.println("tryLockTest----current thread get the lock: " + Thread.currentThread().getName());}finally {rlock.unlock();System.out.println("tryLockTest----current thread release the lock: " + Thread.currentThread().getName());}}else {System.out.println("tryLockTest----current thread CAN NOT get the lock: " + Thread.currentThread().getName());}}public static void main(String[] args){TestLockAndTryLock lockAndTryLock = new TestLockAndTryLock();Thread lockThread = new Thread(() -> lockAndTryLock.lockTest(), "Lock-Thread" );Thread tryLockThread = new Thread(() -> lockAndTryLock.tryLockTest(), "TryLock-Thread" );tryLockThread.start();lockThread.start();}}
输出结果:
lock()方法先获取锁,然后在执行任务的时候阻塞,tryLock()会在尝试加锁失败的时候返回false.package com.springcloud.server.springserver.thread;import java.util.concurrent.TimeUnit;
import java.util.concurrent.locks.ReentrantLock;public class TestLockAndTryLock1 {private ReentrantLock rlock = new ReentrantLock();private void lockTest(){long currentTime = System.currentTimeMillis();try {rlock.lock();System.out.println("lockTest----current thread get the lock: " + Thread.currentThread().getName());while (System.currentTimeMillis() - currentTime <= 5000){//assume do something}}finally {rlock.unlock();System.out.println("lockTest----current thread release the lock: " + Thread.currentThread().getName());}}private void tryLockInterruptTest(){long currentTime = System.currentTimeMillis();while (System.currentTimeMillis() - currentTime <= 100){//assume do something}try {System.out.println("Begin time: " + System.currentTimeMillis());if (rlock.tryLock(1, TimeUnit.SECONDS)){try {System.out.println("tryLockInterruptTest----current thread get the lock: " + Thread.currentThread().getName());}finally {rlock.unlock();System.out.println("tryLockInterruptTest----current thread release the lock: " + Thread.currentThread().getName());}}else {System.out.println("End time: " + System.currentTimeMillis());System.out.println("tryLockInterruptTest----current thread CAN NOT get the lock: " + Thread.currentThread().getName());}} catch (InterruptedException e) {e.printStackTrace();}}public static void main(String[] args){TestLockAndTryLock1 lockAndTryLock = new TestLockAndTryLock1();Thread lockThread = new Thread(() -> lockAndTryLock.lockTest(), "Lock-Thread" );Thread tryLockInterruptThread = new Thread(() -> lockAndTryLock.tryLockInterruptTest(), "TryLockInterrupt-Thread");tryLockInterruptThread.start();lockThread.start();}}输出结果:
lock()方法先获取锁,然后执行任务5秒,tryLock()方法先直接获取锁,获取不到就在1秒的时间内持续获取锁,超过时间还获取不到就返回false.package com.springcloud.server.springserver.thread;import java.util.concurrent.TimeUnit;
import java.util.concurrent.locks.ReentrantLock;public class TestLockAndTryLock2 {private ReentrantLock rlock = new ReentrantLock();private void lockTest(){long currentTime = System.currentTimeMillis();try {rlock.lock();System.out.println("lockTest----current thread get the lock: " + Thread.currentThread().getName());while (System.currentTimeMillis() - currentTime <= 5000){//assume do something}}finally {rlock.unlock();System.out.println("lockTest----current thread release the lock: " + Thread.currentThread().getName());}}private void tryLockInterruptTest(){long currentTime = System.currentTimeMillis();while (System.currentTimeMillis() - currentTime <= 100){//assume do something}try {System.out.println("Begin time: " + System.currentTimeMillis());if (rlock.tryLock(3, TimeUnit.SECONDS)){try {System.out.println("tryLockInterruptTest----current thread get the lock: " + Thread.currentThread().getName());}finally {rlock.unlock();System.out.println("tryLockInterruptTest----current thread release the lock: " + Thread.currentThread().getName());}}else {System.out.println("End time: " + System.currentTimeMillis());System.out.println("tryLockInterruptTest----current thread CAN NOT get the lock: " + Thread.currentThread().getName());}} catch (InterruptedException e) {System.out.println("tryLockInterruptTest Interrupt----current thread is interrupted: " + Thread.currentThread().getName());}}public static void main(String[] args){TestLockAndTryLock2 lockAndTryLock = new TestLockAndTryLock2();Thread lockThread = new Thread(() -> lockAndTryLock.lockTest(), "Lock-Thread" );Thread tryLockInterruptThread = new Thread(() -> lockAndTryLock.tryLockInterruptTest(), "TryLockInterrupt-Thread");tryLockInterruptThread.start();lockThread.start();try {Thread.sleep(100);} catch (InterruptedException e) {System.out.println(Thread.currentThread().getName() + "is interrupted now. ");}tryLockInterruptThread.interrupt();}}lock()方法先获取锁,然后执行任务5秒,tryLock()方法先直接获取锁,获取不到就在1秒的时间内持续获取锁,在获取锁的过程中,主线程(main)以通知的方式中断tryLockInterruptThread线程,tryLock()方法可以响应中断.
package com.springcloud.server.springserver.thread;import java.util.concurrent.TimeUnit;
import java.util.concurrent.locks.Lock;
import java.util.concurrent.locks.ReentrantLock;public class TestLockInterruptibly {final Lock lock = new ReentrantLock();public static void main(String[] args) throws Exception {TestLockInterruptibly testLockInterruptibly = new TestLockInterruptibly();Thread lockThread = new Thread(() -> testLockInterruptibly.lock());Thread interruptiblyThread = new Thread(() -> testLockInterruptibly.lockInterruptibly());lockThread.start();interruptiblyThread.start();TimeUnit.SECONDS.sleep(2);
// interruptiblyThread.interrupt();}public void lockInterruptibly() {long currentTime = System.currentTimeMillis();while (System.currentTimeMillis() - currentTime <= 500){//assume do something}try {lock.lockInterruptibly();System.out.println("lockInterruptibly获取Lock锁");} catch (InterruptedException e) {System.out.println("lockInterruptibly捕捉InterruptedException异常");}finally {lock.unlock();System.out.println("lockInterruptibly释放Lock锁");}}public void lock() {long currentTime = System.currentTimeMillis();try {lock.lock();System.out.println("lock获取Lock锁");while (System.currentTimeMillis() - currentTime <= 5000){//assume do something}}finally {lock.unlock();System.out.println("lock释放Lock锁");}}}一般情况下,lockInterruptibly()会阻塞直到获取lock锁,此时和普通的lock()作用差不多,输出结果:
当我们打开main方法里面的注释,结果就不一样了,输出结果:
lockInterruptibly()在阻塞的过程中可以响应中断,并可以结束线程.此处抛异常原因是并没有获取锁,却去解锁(unLock()),普通的lock()方法无法响应中断.
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