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、設置公平鎖
【注】使用reentrantlock時，一定要釋放鎖，一般釋放放到finnal里寫。
提供以下重要的方法
- lock():獲得鎖，如果鎖已被占用，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
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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執行后被打斷
例子2
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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。打斷后firstthread執行結束了，secondthread得到鎖，繼續執行
例子3
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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$1.run(reentrantlocktest2.java:22)
at java.lang.thread.run(thread.java:748)
locked:secondthread
unlocked:secondthread
分析：firstthread先獲得鎖執行，secondthread在等待，此時中斷并未打斷等待。firstthread執行完，secondthread獲取后被打斷
例子4
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public class reentrantlocktest2 { reentrantlock lock; reentrantlocktest2(reentrantlock lock) { this.lock = lock; } private runnable getrunnable() { return new runnable() { @override public void run() { while (true) { try { try {// lock.lock(); lock.lockinterruptibly(); system.out.println("locked:" + thread.currentthread().getname()); thread.sleep(800); break; } finally { lock.unlock(); system.out.println("unlocked:" + thread.currentthread().getname()); } } catch (interruptedexception e) { e.printstacktrace(); } } } }; } public static void main(string[] args) { reentrantlock lock = new reentrantlock(); reentrantlocktest2 test = new reentrantlocktest2(lock); reentrantlocktest2 test2 = new reentrantlocktest2(lock); thread thread1 = new thread(test.getrunnable(), "firstthread"); thread thread2 = new thread(test2.getrunnable(), "secondthread"); thread1.start(); thread2.start(); try { thread.sleep(600); }catch (interruptedexception e) { e.printstacktrace(); } system.out.println("interupt begin"); thread2.interrupt(); system.out.println("interupt end"); }} |
一次執行結果
locked:firstthread
interupt begin
interupt end
exception in thread "secondthread" java.lang.illegalmonitorstateexception
at java.util.concurrent.locks.reentrantlock$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
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