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
- 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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