Question

I have a multi thread application.

One thread inserts in a queue and many thread reads form this queue. In order to read properly, reader threads lock the queue like the following code.

My question is: Does the inserter thread become blocked when the following code is called by reader threads since it uses the same queue? Or it continues inserting without interruption?

lock ( MsgQueue ) {
    if ( MsgQueue.Count == 0 ) {
         Monitor.Wait( MsgQueue );
         continue;
    }
    msg = MsgQueue.Dequeue( );
}

Answer 1

The inserter thread is being blocked at points, yes.

    lock ( MsgQueue ) {
        if ( MsgQueue.Count == 0 ) {  // LINE 1
            Monitor.Wait( MsgQueue ); // LINE 2
            continue;
        }
        msg = MsgQueue.Dequeue( ); // LINE 3
    }

At line 1 the lock is held by the reader, so the inserter is blocked.

At line 2 the lock is released, and not reacquired until the inserter presumably calls Monintor.Pulse on MsgQueue.

At line 3 the lock is still being held (from line 1), and afterwards it is released again due to exiting the lock scope.