java ReentrantLock
介紹
ReentrantLock稱為重入鎖,比內部鎖synchonized擁有更強大的功能,它可中斷、可定時、設定公平鎖
【注】使用ReentrantLock時,一定要釋放鎖,一般釋放放到finnal裡寫。
提供以下重要的方法
lock():獲得鎖,如果鎖已被佔用,則等待
lockInterruptibly():獲得鎖,但有限響應中斷
unlock():釋放鎖
tryLock():嘗試獲取鎖。如果獲得,返回true;否則返回false
tryLock(long time, TimeUnit unit):在給定時間內獲得鎖。如果獲得返回true;否則返回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"); } }
一次執行結果:
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執行,secondThread不停的判斷是否可以獲得鎖,當firstThread執行完,secondThread執行後被打斷
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"); } }
一次執行結果
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執行,secondThread等待,等待過程被打斷。打斷後firstThread執行結束了,secondThread得到鎖,繼續執行
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"); } }
一次執行結果
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$1.run(ReentrantLockTest2.java:22) at java.lang.Thread.run(Thread.java:748) Locked:secondThread UnLocked:secondThread
分析:firstThread先獲得鎖執行,secondThread在等待,此時中斷並未打斷等待。firstThread執行完,secondThread獲取後被打斷
例子4
public class ReentrantLockTest2 { ReentrantLock lock; ReentrantLockTest2(ReentrantLock lock) { this.lock = lock; } private Runnable getRunnable() { return new Runnable() { @Override public void run() { while (true) { try { try { //lock.lock(); lock.lockInterruptibly(); System.out.println("Locked:" + Thread.currentThread().getName()); Thread.sleep(800); break; } finally { lock.unlock(); System.out.println("UnLocked:" + Thread.currentThread().getName()); } } catch (InterruptedException e) { e.printStackTrace(); } } } }; } public static void main(String[] args) { ReentrantLock lock = new ReentrantLock(); ReentrantLockTest2 test = new ReentrantLockTest2(lock); ReentrantLockTest2 test2 = new ReentrantLockTest2(lock); Thread thread1 = new Thread(test.getRunnable(), "firstThread"); Thread thread2 = new Thread(test2.getRunnable(), "secondThread"); thread1.start(); thread2.start(); try { Thread.sleep(600); }catch (InterruptedException e) { e.printStackTrace(); } System.out.println("interupt begin"); thread2.interrupt(); System.out.println("interupt end"); } }
一次執行結果
Locked:firstThread interupt begin interupt end Exception in thread "secondThread" java.lang.IllegalMonitorStateException at java.util.concurrent.locks.ReentrantLock$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();在執行過程中可以響應中斷時間