java ReentrantLock詳解
介紹
ReentrantLock稱為重入鎖，比內(nèi)部鎖synchonized擁有更強(qiáng)大的功能，它可中斷、可定時(shí)、設(shè)置公平鎖
【注】使用ReentrantLock時(shí)，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(yīng)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(shí)間內(nèi)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(zhí)行結(jié)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(zhí)行，secondThread不停的判斷是否可以獲得鎖，當(dāng)firstThread執(zhí)行完，secondThread執(zhí)行后被打斷
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(zhí)行結(jié)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(zhí)行，secondThread等待，等待過程被打斷。打斷后firstThread執(zhí)行結(jié)束了，secondThread得到鎖，繼續(xù)執(zhí)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(zhí)行結(jié)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$1.run(ReentrantLockTest2.java:22)
at java.lang.Thread.run(Thread.java:748)
Locked:secondThread
UnLocked:secondThread
分析：firstThread先獲得鎖執(zhí)行，secondThread在等待，此時(shí)中斷并未打斷等待。firstThread執(zhí)行完，secondThread獲取后被打斷
例子4
public class ReentrantLockTest2 {
ReentrantLock lock;
ReentrantLockTest2(ReentrantLock lock) {
this.lock = lock;
}
private Runnable getRunnable() {
return new Runnable() {
@Override
public void run() {
while (true) {
try {
try {
// lock.lock();
lock.lockInterruptibly();
System.out.println("Locked:" + Thread.currentThread().getName());
Thread.sleep(800);
break;
} finally {
lock.unlock();
System.out.println("UnLocked:" + Thread.currentThread().getName());
}
} catch (InterruptedException e) {
e.printStackTrace();
}
}
}
};
}
public static void main(String[] args) {
ReentrantLock lock = new ReentrantLock();
ReentrantLockTest2 test = new ReentrantLockTest2(lock);
ReentrantLockTest2 test2 = new ReentrantLockTest2(lock);
Thread thread1 = new Thread(test.getRunnable(), "firstThread");
Thread thread2 = new Thread(test2.getRunnable(), "secondThread");
thread1.start();
thread2.start();
try {
Thread.sleep(600);
}catch (InterruptedException e) {
e.printStackTrace();
}
System.out.println("interupt begin");
thread2.interrupt();
System.out.println("interupt end");
}
}
一次執(zhí)行結(jié)果
Locked:firstThread
interupt begin
interupt end
Exception in thread "secondThread" java.lang.IllegalMonitorStateException
at java.util.concurrent.locks.ReentrantLock$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(zhí)行過程中可以響應(yīng)中斷時(shí)間
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