[英]Java Non Reentrant Lock Implementation
我已经实现了非重入锁。 我想知道这是否有任何错误,运行条件等。我知道必须使用现有库的事实(而不是编写我们自己的库),但这只是为了查看我是否正确理解了Java并发性。 任何反馈表示赞赏。
public class MyLock {
private boolean isLocked = false;
private long owner = -1;
private static String TAG = "MyLock: ";
public synchronized void Lock() throws InterruptedException, IllegalStateException {
if(!isLocked) {
isLocked = true;
owner = Thread.currentThread().getId();
} else {
if(owner == Thread.currentThread().getId()) {
throw new IllegalStateException("Lock already acquired. " +
"This lock is not reentrant");
} else {
while(isLocked == true) {
System.out.println(TAG+"Waiting for Lock, Tid = " +
Thread.currentThread().getId());
wait();
}
}
}
System.out.println(TAG+"Lock Acquired: Owner = " + owner);
}
public synchronized void Unlock() throws IllegalStateException {
if(!isLocked || owner != Thread.currentThread().getId()) {
throw new IllegalStateException("Only Owner can Unlock the lock");
} else {
System.out.println(TAG+"Unlocking: Owner = " + owner);
owner = -1;
isLocked = false;
notify();
}
}
}
这是Java中“标准” /“非可重入”锁的实现,作为Java内置的ReentrantLock的包装,它只是防止多次获得该锁。
/**
* A "non-reentrant" lock, implemented as a wrapper around Java's ReentrantLock.
*
*/
class StandardLock implements java.util.concurrent.locks.Lock {
public static class LockAlreadyHeldException extends RuntimeException {}
private final java.util.concurrent.locks.ReentrantLock mainLock;
private void checkNotAlreadyHeld() {
if (mainLock.getHoldCount()!=0) {
throw new LockAlreadyHeldException();
}
}
public StandardLock() {
mainLock=new java.util.concurrent.locks.ReentrantLock();
}
public StandardLock(boolean fair) {
mainLock=new java.util.concurrent.locks.ReentrantLock(fair);
}
@Override
public void lock() {
checkNotAlreadyHeld();
mainLock.lock();
}
@Override
public void lockInterruptibly() throws InterruptedException {
checkNotAlreadyHeld();
mainLock.lockInterruptibly();
}
@Override
public boolean tryLock() {
checkNotAlreadyHeld();
return mainLock.tryLock();
}
@Override
public boolean tryLock(long time, TimeUnit unit) throws InterruptedException {
checkNotAlreadyHeld();
return mainLock.tryLock(time, unit);
}
@Override
public void unlock() {
mainLock.unlock();
}
@Override
public Condition newCondition() {
return mainLock.newCondition();
}
}
这种方法的优点是该类实现了Java的Lock接口,因此附带了Condition Variables,以便允许创建Monitors。 监视器对于充分利用锁进行并行编程很重要。
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