java - 我如何将 ReentrantReadWriteLock.readLock 或 ReentrantReadWriteLock.writeLock 转换为我的类对象

Question

我想要做的是让当前线程一次保持读取计数的数量。我为此编写了一个包装器，但我的问题是 ReadLock() 方法正在返回 ReentrantReadWriteLock.WriteLock 所以我没有多余的getThreadReadLockCount 之后。我想要的是 readLock() 方法应该返回我，这样我就可以有多余的 count 方法。有任何想法吗。？

   private final ThreadLocal    readLocksHeldByThread;

private static class ReadCounts {
    public int  value   = 0;
}

public CustomReentrantReadWriteLock() {
    super(true);
    readLocksHeldByThread = new ThreadLocal() {
        @Override
        public Object initialValue() {
            return new ReadCounts();
        }
    };
}

@Override
public synchronized ReadLock readLock() {
    final ReadCounts myReadLocks = (ReadCounts) readLocksHeldByThread.get();
    ++myReadLocks.value;
    return super.readLock();
}

    public synchronized int getThreadReadLockCount() {
    final ReadCounts currentReadLocks = (ReadCounts) readLocksHeldByThread.get();
    return currentReadLocks.value;
}

Answer 1

您的代码只计算线程请求读锁的次数，如果它在锁定和释放之间被缓存，这将产生不同的结果：

Lock rl = var.readLock();
rl.lock();
try{
    //...
}finally{
    rl.unlock();
}

对比

var.readLock().lock();
try{
    //...
}finally{
    var.readLock().unlock();
}

会给出不同的结果

你可以像这样包裹返回的锁

@Override public Lock readLock() {
     final ReadCounts myReadLocks = (ReadCounts) readLocksHeldByThread.get();
     return new Lock(){
        Lock l = super.readLock(); 
        public void lock(){
            l.lock();
            ++myReadLocks.value;
        }

        public void lockInterruptibly() throws InterruptedException{
            l.lockInterruptibly();
            ++myReadLocks.value;
        }

        public boolean tryLock(){
            if(l.tryLock()){
                ++myReadLocks.value;
                return true;
            }else return false;
        }

        public boolean tryLock(long time, TimeUnit unit) throws InterruptedException{
            if(l.tryLock(time,unit)){
                ++myReadLocks.value;
                return true;
            }else return false;
        }

        public void unlock(){
            --myReadLocks.value;
            l.unlock();
        }

        public Condition newCondition(){
            return l.newCondition();
        }

     }
}