java ReentrantLock详解

2019-11-26 09:07:46

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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

【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.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
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();  try {   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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