CODEWITHSUNDEEP
c#.netasynchronous.net-core
dibr77
dibr77

Reputation: 49

Why to limit the amount of concurrent async I/O operations?

If I have to make simultaneously 100 of async queries to some URL. My code looks like this:

var tasks = requests.Select(x => httpClient.GetStringAsync(x)).ToList();
return Task.WhenAll(tasks);

Should I care about the limitation of concurrent calls? It means, don't create 100 tasks simultaneously, but do it by chunks. Good post on this subject is here.

I prefer rely on ServicePointManager.DefaultConnectionLimit instead. Windows OS limits the number of outbound connections. Look here. So, I'm creating 100 Tasks and only 10 of them (DefaultConnectionLimit default) are running in parallel.

Inspired by How to limit the amount of concurrent async I/O operations?.

Upvotes: 1

Views: 296

Answers (1)

Stefan
Stefan

Reputation: 17648

Yes, you should care about the limitation of concurrent calls; but only as per use case.

Bottom line: it depends on your infrastructure.

For example, if you are on a shared network connection; fetching a lot of data from different sources can clog your network.

Another example: writing to a network server might be more efficient when doing so in larger chuncsk, with fewer simultaneous connections.

Depending on where you run this, it worth to know how many possible parallel tasks are being executed.

If you know that, you can tweak it to be reasonable within the boundaries of your environment. This depends on the hardware and the possible load....

That's basically what's meant in the article by:

The optimum number of connections depends on the actual conditions in which the application runs. Increasing the number of connections available to the application may not affect application performance. To determine the impact of more connections, run performance tests while varying the number of connections.

The default of the HttpWebRequest, as described, is pretty low. Which would result in a pretty good "general approach" scenario, even on home/consumers internet connections. If your situation is e.g.: high performant server to server communication, then, different values would make more sense.

The key is to know the environment/context and it's capabilities.

Then you can determine a good number of parralel operations.

And that's why you must care about it, and sometimes limit it :-)

Upvotes: 3

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