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
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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" );
}
}
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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
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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" );
}
}
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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
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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" );
}
}
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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$1.run(reentrantlocktest2.java:22)
at java.lang.thread.run(thread.java:748)
locked:secondthread
unlocked:secondthread
分析:firstthread先获得锁执行,secondthread在等待,此时中断并未打断等待。firstthread执行完,secondthread获取后被打断
例子4
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public class reentrantlocktest2 {
reentrantlock lock;
reentrantlocktest2(reentrantlock lock) {
this .lock = lock;
}
private runnable getrunnable() {
return new runnable() {
@override
public void run() {
while ( true ) {
try {
try {
// lock.lock();
lock.lockinterruptibly();
system.out.println( "locked:" + thread.currentthread().getname());
thread.sleep( 800 );
break ;
} finally {
lock.unlock();
system.out.println( "unlocked:" + thread.currentthread().getname());
}
} catch (interruptedexception e) {
e.printstacktrace();
}
}
}
};
}
public static void main(string[] args) {
reentrantlock lock = new reentrantlock();
reentrantlocktest2 test = new reentrantlocktest2(lock);
reentrantlocktest2 test2 = new reentrantlocktest2(lock);
thread thread1 = new thread(test.getrunnable(), "firstthread" );
thread thread2 = new thread(test2.getrunnable(), "secondthread" );
thread1.start();
thread2.start();
try {
thread.sleep( 600 );
} catch (interruptedexception e) {
e.printstacktrace();
}
system.out.println( "interupt begin" );
thread2.interrupt();
system.out.println( "interupt end" );
}
}
|
一次执行结果
locked:firstthread
interupt begin
interupt end
exception in thread "secondthread" java.lang.illegalmonitorstateexception
at java.util.concurrent.locks.reentrantlock$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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