java ReentrantLock详解

java ReentrantLock详解

介绍

ReentrantLock称为重入锁，比内部锁synchonized拥有更强大的功能，它可中断、可定时、设置公平锁

【http://注】使用ReentrantLock时，一定要释放锁，一般释放放到finnal里写。

提供以下重要的方法

lock():获得锁，如果锁已被占用，则等待

lockInterruptibly():获得锁，但有限响应中断

unlock():释放锁

tryLock():尝试获取锁。如果获得，返回true；否则返回false

tryLock(long time, TimeUnit unit):在给定时间内获得锁。如果获得返回true；否则返回false

示例

例子1

import java.util.concurrent.locks.ReentrantLock;

public class ReentrantLockTest {

ReentrantLock lock;

ReentrantLockTest(ReentrantLock lock) {

this.lock = lock;

}

private Runnable getRunnable() {

return new Runnable() {

@Override

public void run() {

while(true) {

try {

if (lock.tryLock()) {

try {

System.out.println("Locked:" + Thread.currentThread().getName());

Thread.sleep(800);

} finally {

lock.unlock();

System.out.println("UnLocked:" + Thread.currentThread().getName());

}

System.out.println("break before");

break;

} else {

//System.out.println("Unable to lock " + Thread.currentThread().getName());

}

} catch (InterruptedException e){

System.out.println(Thread.currentThread() + " is Interupted");

e.printStackTrace();

}

}

}

};

}

public static void main(String[] args) {

ReentrantLock lock = new ReentrantLock();

ReentrantLockTest test = new ReentrantLockTest(lock);

ReentrantLockTest test2 = new ReentrantLockTest(lock);

Thread thread1 = new Thread(test.getRunnable(), "firstThread");

Thread thread2 = new Thread(test2.getRunnable(), "secondThread");

thread1.start();

thread2.start();

try {

Thread.sleep(300);

}catch (InterruptedException e) {

e.printStackTrace();

}

System.out.println("interupt begin");

thread2.interrupt();

System.out.println("interupt end");

}

}

一次执行结果：

Locked:firstThread

interupt begin

interupt end

UnLocked:firstThread

break before

Locked:secondThread

UnLocked:secondThread

Thread[secondThread,5,main] is Interupted

java.lang.InterruptedException: sleep interrupted

    at java.lang.Thread.sleep(Native Method)

    at com.jihite.templet.JavaBase.ReentrantLockTest$1.run(ReentrantLockTest.java:23)

    at java.lang.Thread.run(Thread.java:748)

Locked:secondThread

UnLocked:secondThread

break before

分析：firstThread执行，secondThread不停的判断是否可以获得锁，当firstThread执行完，secondThread执行后被打断

例子2

import java.util.concurrent.TimeUnit;

import java.util.concurrent.locks.ReentrantLock;

public class ReentrantLockTest {

ReentrantLock lock;

ReentrantLockTest(ReentrantLock lock) {

this.lock = lock;

}

private Runnable getRunnable() {

return new Runnable() {

@Override

public void run() {

while(true) {

try {

if (lock.tryLock(700, TimeUnit.MILLISECONDS)) {

try {

System.out.println("Locked:" + Thread.currentThread().getName());

Thread.sleep(800);

} finally {

lock.unlock();

System.out.println("UnLocked:" + Thread.currentThread().getName());

}

System.out.println("break before");

break;

} else {

//System.out.println("Unable to lock " + Thread.currentThread().getName());

}

} catch (InterruptedException e){

System.out.println(Thread.currentThread() + " is Interupted");

e.printStackTrace();

}

}

}

};

}

public static void main(String[] args) {

ReentrantLock lock = new ReentrantLock();

ReentrantLockTest test = new ReentrantLockTest(lock);

ReentrantLockTest test2 = new ReentrantLockTest(lock);

Thread thread1 = new Thread(test.getRunnable(), "firstThread");

Thread thread2 = new Thread(test2.getRunnable(), "secondThread");

thread1.start();

thread2.start();

try {

Thread.sleep(300);

}catch (InterruptedException e) {

e.printStackTrace();

}

System.out.println("interupt begin");

thread2.interrupt();

System.out.println("interupt end");

}

}

一次执行结果

Locked:firstThread

interupt begin

interupt end

Thread[secondThread,5,main] is Interupted

java.lang.InterruptedException

    at java.util.concurrent.locks.AbstractQueuedSynchronizer.doAcquireNanos(AbstractQueuedSynchronizer.java:936)

    at java.util.concurrent.locks.AbstractQueuedSynchronizer.tryAcquireNanos(AbstractQueuedSynchronizer.java:1247)

    at java.util.concurrent.locks.ReentrantLock.tryLock(ReentrantLock.java:442)

    at com.jihite.templet.JavaBase.ReentrantLockTest$1.run(ReentrantLockTest.java:19)

    at java.lang.Thread.run(Thread.java:748)

Locked:secondThread

UnLocked:firstThread

break before

UnLocked:secondThread

break before

分析：firstThread执行，secondThread等待，等待过程被打断。打断后firstThread执行结束了，secondThread得到锁，继续执行

例子3

import java.util.concurrent.locks.ReentrantLock;

public class ReentrantLockTest2 {

ReentrantLock lock;

ReentrantLockTest2(ReentrantLock lock) {

this.lock = lock;

}

private Runnable getRunnable() {

return new Runnable() {

@Override

public void run() {

while (true) {

try {

try {

lock.lock();

// lock.lockInterruptibly();

System.out.println("Locked:" + Thread.currentThread().getName());

Thread.sleep(800);

break;

} finally {

lock.unlock();

System.out.println("UnLocked:" + Thread.currentThread().getName());

}

} catch (InterruptedException e) {

e.printStackTrace();

}

}

}

};

}

public static void main(String[] args) {

ReentrantLock lock = new ReentrantLock();

ReentrantLockTest2 test = new ReentrantLockTest2(lock);

ReentrantLockTest2 test2 = new ReentrantLockTest2(lock);

Thread thread1 = new Thread(test.getRunnable(), "firstThread");

Thread thread2 = new Thread(test2.getRunnable(), "secondThread");

thread1.start();

thread2.start();

try {

Thread.sleep(600);

}catch (InterruptedException e) {

e.printStHsfAkyackTrace();

}

System.out.println("interupt begin");

thread2.interrupt();

System.out.println("interupt end");

}

}

一次执行结果

Locked:firstThread

interupt begin

interupt end

UnLocked:firstThread

Locked:secondThread

UnLocked:secondThread

java.lang.InterruptedException: sleep interrupted

    at java.lang.Thread.sleep(Native Method)

    at com.jihite.templet.JavaBase.ReentrantLockTest2$1.run(ReentrantLockTest2.java:22)

    at java.lang.Thread.run(Thread.java:748)

Locked:secondThread

UnLocked:secondThread

分析：firstThread先获得锁执行，secondThread在等待，此时中断并未打断等待。firstThread执行完，secondThread获取后被打断

例子4

public class ReentrantLockTest2 {

ReentrantLock lock;

ReentrantLockTest2(ReentrantLock lock) {

this.lock = lock;

}

private Runnable getRunnable() {

return new Runnable() {

@Override

public void run() {

while (true) {

try {

try {

// lock.lock();

lock.lockInterruptibly();

System.out.println("Locked:" + Thread.currentThread().getName());

Thread.sleep(800);

break;

} finally {

lock.unlock();

System.out.println("UnLocked:" + Thread.currentThread().getName());

}

} catch (InterruptedException e) {

e.printStackTrace();

}

}

}

};

}

public static void main(String[] args) {

ReentrantLock lock = new ReentrantLock();

ReentrantLockTest2 test = new ReentrantLockTest2(lock);

ReentrantLockTest2 test2 = new ReentrantLockTest2(lock);

Thread thread1 = new Thread(test.getRunnable(), "firstThread");

Thread thread2 = new Thread(test2.getRunnable(), "secondThread");

thread1.start();

thread2.start();

HsfAkytry {

Thread.sleep(600);

}catch (InterruptedException e) {

e.printStackTrace();

}

System.out.println("interupt begin");

thread2.interrupt();

System.out.println("interupt end");

}

}

一次执行结果

Locked:firstThread

interupt begin

interupt end

Exception in thread "secondThread" java.lang.IllegalMonitorStateException

    at java.util.concurrent.locks.ReentrantLock$Sync.tryRelease(ReentrantLock.java:151)

    at java.util.concurrent.locks.AbstractQueuedSynchronizer.release(AbstractQueuedSynchronizer.java:1261)

    at java.util.concurrent.locks.ReentrantLock.unlock(ReentrantLock.java:457)

    at com.jihite.templet.JavaBase.ReentrantLockTest2$1.run(ReentrantLockTest2.java:25)

    at java.lang.Thread.run(Thread.java:748)

分析：lock.lockInterruptibly();在执行过程中可以响应中断时间

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