ReentrantReadWriteLock

ReentrantReadWriteLock

据说ReentrantReadWriteLock是供一位作者和多位读者使用的。

但是,读取器应该等待,直到缓冲区中存在一些数据为止。

那么,要锁定什么?

我创建了并发对象,如下所示:

private final ReentrantReadWriteLock rwl = new ReentrantReadWriteLock();
protected final Lock readLock = rwl.readLock();
protected final Lock writeLock = rwl.writeLock();
protected final Condition hasData = writeLock.newCondition();

现在在写方法中,我这样做:
writeLock.lock();

// writing first portion and updating variables

hasData.signalAll();

// if required then writing second portion and updating variables

hasData.signalAll();

但是如何写一个读者呢?它应该只获取readLock吗?但是,它如何才能等待信号呢?如果它还需要一个writeLock,那么读/写锁定的最高权限在哪里?

如果仅由writeLock保护所需的变量,如何确保它们在读取期间不会改变?

队列不匹配任务

这是关于ReentrantReadWriteLock的问题。

最佳答案

ReentrantReadWriteLock确实有点令人困惑,因为readLock没有条件。
您必须在阅读器中升级到writeLock才能等待这种情况。

在作家中。

writeLock.lock(); //locks all readers and writers
// do write data
hasData.signalAll();
writeLock.unlock();

在阅读器中,您可以执行以下操作:
readLock.lock(); //blocks writers only
try{
 if(!checkData()) //check if there's data, don't modify shared variables
 {
  readLock.unlock();
  writeLock.lock(); // need to lock the writeLock to allow to use the condition.
                    // only one reader will get the lock, other readers will wait here
  try{
   while(!checkData()) // check if there' still no data
   {
     hasData.await(); //will unlock and re-lock after writer has signalled and unlocked.
   }
   readLock.lock();    // continue blocking writer
  }
  finally
  {
    writeLock.unlock(); //let other readers in
  }
 }
 //there should be data now
 readData(); // don't modify variables shared by readers.
}
finally
{
  readlock.unlock(); //let writers in
}

为了完整起见,当然,每个unlock()应该放在一个finally块中。

09-12 16:17