// Acquire the lock for read (shared) access
public void LockRead()
{
lock (monitor) {
// if there isn’t blocked writers and the resource isn’t being written, grant
// read access immediately
if (writeReqQueue.Count == 0 && state >= 0)
{
state++; // add one reader
return;
}
// otherwise, enqueue a read access request
LockReadRequest request = EnqueueReader();
// wait until request is granted, or the thread gives up due to interruption
do
{
try {
MonitorEx.Wait(monitor, monitor); // eq a Monitor.Wait(monitor);
} catch (ThreadInterruptedException) {
// if the requested shared access was granted, we must re-assert interrupt
// exception, and return normally.
if (request.done)
{
Thread.CurrentThread.Interrupt();
break;
}
// otherwise, we remove the request from the queue and re-throw the exception
RemoveReader();
throw;
}
// if shared access was granted then return; otherwise, re-wait
} while (!request.done);
}
}
/*
* Methods that implement the lock read request queue
*/
private LockReadRequest EnqueueReader()
{
if (readReqQueue == null)
{
readReqQueue = new LockReadRequest();
}
else
{
readReqQueue.waiters++;
}
return(readReqQueue);
}
private void ClearReaderQueue()
{
readReqQueue = null;
}