Java非重入鎖實現

Question

我已經實現了非重入鎖。 我想知道這是否有任何錯誤，運行條件​​等。我知道必須使用現有庫的事實（而不是編寫我們自己的庫），但這只是為了查看我是否正確理解了Java並發性。 任何反饋表示贊賞。

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();
    }
}

}

Answer 1

這是Java中“標准” /“非可重入”鎖的實現，作為Java內置的ReentrantLock的包裝，它只是防止多次獲得該鎖。

/**
 * 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();
    }
}

這種方法的優點是該類實現了Java的Lock接口，因此附帶了Condition Variables，以便允許創建Monitors。 監視器對於充分利用鎖進行並行編程很重要。