How to marshal work onto single thread c#

Question

I have an app that needs to process some packets from a UDP broadcast, and write the result to a SQL database. During intervals the rate of incoming packets gets quite high, and I find that the underlying buffer overflows, even at 8MB, because of the slow database writing.

To solve this I have come up with two options, cache some of the DB writing, and/or marshal the db writes onto another sequentially operating thread. (order of db writes must be preserved).

My question is how to marshal the work most effectively, with built-in structures/features of c#?

Should I just have a synchronized queue, put the delegate work items onto it and have a single thread service it in an event loop?

You need to aggregate the DB writes so that you don't wind up with one transaction for each packet received. Otherwise you'll be clamped at about 30 transactions per second or so due to the rotational speed of the media. — David Schwartz, May 16 '12 at 08:55
You've got a pretty fundamental data flow problem here. Threading is not going to be a magic fix since you burn so few real cpu cycles. Using TCP instead of UDP would be a simple fix. Or a bigger buffer, including writing to local disk, assuming the fire hose is turned off long enough to allow you to catch up. — Hans Passant, May 16 '12 at 10:11
I agree 100% with both David and Hans, (what is wrong with me today?). Fixing your DB transactions with bulk updates and/or stored procedures will improve your DB performance and may allow you to keep up with the data. If not, then you will have to apply flow-control somehow. I appreciate that UDP broadcast has no provision whatsoever for flow-control and that other broadcast receivers may not want the data slowed up, but I don't see much choice. Can you put your DB on an SSD? — Martin James, May 16 '12 at 14:03
Yes, we are planning on putting the DB on an SSD, and also have it assigned a large amount of ram to allow it to run predominantly in-memory. — Vort3x, May 16 '12 at 21:32

adrianm · Accepted Answer · 2012-05-16T13:41:36.590

The easiest way is to create a separate thread for the UDP reading.

The thread just receives the packages and puts them into a BlockingCollection. (Don't know how you do the packet reading so this will be pseudocode)

BlockingCollection<Packet> _packets = new BlockingCollection<Packet>();
...

while (true) {
    var packet = udp.GetNextPacket();
    _packets.Add(packet);
}

This will ensure you don't miss any packages because the reading thread is busy.

Then you create a worker thread that does the same thing as your current code but it reads from the blockingcollection instead.

while (true) {
   var nextPacket = _packets.Take();
   ...
}

If your packages are independent (which they should be since you use UDP) you can fire up several worker threads.

score 1 · Answer 2 · answered May 16 '12 at 08:57

If you are using .Net 4, Tasks and TaskSchedulers can help you out here. On MSDN you'll find the LimitedConcurrencyLevelTaskScheduler. Create a single instance of that, with a concurrency level of 1, and each time you have work to do, create a Task and schedule it with that scheduler.

How to marshal work onto single thread c#

2 Answers2