How to work threading with ConcurrentQueue

Question

I am trying to figure out what the best way of working with a queue will be. I have a process that returns a DataTable. Each DataTable, in turn, is merged with the previous

Answer 1

I think ConcurrentQueue is useful only in very few cases. Its main advantage is that it is lock free. However, usually the producer thread(s) have to inform the consumer thread(s) somehow that there is data available to process. This signalling between threads needs locks and negates the benefit of using ConcurrentQueue. The fastest way to synchronize threads is using Monitor.Pulse(), which works only within a lock. All other synchronization tools are even slower.

Of course, the consumer can just continuously check if there is something in the queue, which works without locks, but is a huge waste of processor resources. A little bit better is if the consumer waits between checking.

Raising a thread when writing to the queue is a very bad idea. Using ConcurrentQueue to save maybe 1 microsecond will be completely wasted by executing the eventhandler, which might take 1000 times longer.

If all the processing is done in an event handler or an async call, the question is why still a queue is needed? Better pass the data directly to the handler and don't use a queue at all.

Please note that the implementation of ConcurrentQueue is rather complicated to allow concurrency. In most cases, better use a normal Queue<> and lock every access to the queue. Since the queue access needs only microseconds, it is extremely unlikely that 2 threads access the queue in the same microsecond and there will be hardly ever any delay because of locking. Using a normal Queue<> with locking will often result in faster code execution than ConcurrentQueue.