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

【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

1. lock():获得锁，如果锁已被占用，则等待
2. lockinterruptibly():获得锁，但有限响应中断
3. unlock():释放锁
4. trylock():尝试获取锁。如果获得，返回true；否则返回false
5. 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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