java - 有没有办法从 java.util.concurrent.locks.ReentrantReadWriteLock$ReadLock 获取 java.util.concurrent.locks.ReentrantReadWriteLock 对象

Question

我使用

创建一个 java.util.concurrent.locks.ReentrantReadWriteLock

new java.util.concurrent.locks.ReentrantReadWriteLock().readLock()

然后我将方法作为 Lock 接口(interface)传递给方法

method(Lock lock)

现在我想知道当前线程拥有多少个读锁。我怎样才能实现这个目标？

我无法将其再次转换为 ReentrantReadWriteLock 。我应该怎么办？我怎样才能得到这个计数？

Answer 1

要获取ReentrantReadWriteLock上的读锁计数，需要调用lock.getReadHoldCount()

要单独从 ReadLock 获取此信息，您需要获取“sync”字段并通过反射调用“getReadHoldCount()”。

<小时/>

使用反射访问锁的示例如下。

static void printOwner(ReentrantLock lock) {
    try {
        Field syncField = lock.getClass().getDeclaredField("sync");
        syncField.setAccessible(true);
        Object sync = syncField.get(lock);
        Field exclusiveOwnerThreadField = AbstractOwnableSynchronizer.class.getDeclaredField("exclusiveOwnerThread");
        exclusiveOwnerThreadField.setAccessible(true);
        Thread t = (Thread) exclusiveOwnerThreadField.get(sync);
        if (t == null) {
            System.err.println("No waiter?");
        } else {
            CharSequence sb = Threads.asString(t);
            synchronized (System.out) {
                System.out.println(sb);
            }
        }
    } catch (NoSuchFieldException e) {
        throw new AssertionError(e);
    } catch (IllegalAccessException e) {
        throw new AssertionError(e);
    }
}

<小时/>

您可以做的是创建一个包装器。

class MyLock implements Lock {
     private final ReentrantReadWriteLock underlying; // set in constructor

     public ReentrantReadWriteLock underlying() { return underlying; }
     public void lock() { underlying.readLock().lock(); }
}