c# webclient async

Question

I have inherited a c# application that samples data from ~380 sites via Webclient downloadfileasync. A separate thread is created for each site! (the downloads each wait a timeout period before downloading the next data - so load is not constant....but still!) Anyway, As the number of sites will increase (likely dramatically) over the next year or so, I would like to change this to a few (reasonable number) of worker threads that issue a bunch of Webclient downloadfileasync calls for a subset of the sites. But I am not sure what might happen if multiple downloads complete concurrently - will the downloadfilecompleted event handler be serialized by webclient? Or can multiple webclient completions occur "simultaneously" (or more likely, interleaved)? Will I be running the risk of one completion corrupting another? Or does anyone have a better suggestion on how to manage the explosion of threads in the current implementation?

Thanks in advance.

If you are using DownloadFileAsync it already is in its own thread. So the use of yet another thread is sort of pointless and not very effective. — Security Hound
– Security Hound, Commented Jun 18, 2012 at 18:58
Like Jon Skeet says, a feature of asynchronous tasks is preventing thread blocking. You probably should do a baseline profile of your application in Performance Monitor using some of these counters to be able to compare what adding more sites to your application process will do. It'll also give you a good place to start if you need to do any optimization. — Sixto Saez
– Sixto Saez, Commented Jun 18, 2012 at 18:59

Jon Skeet · Accepted Answer · 2012-06-18 18:49:43Z

2

I would expect multiple completion events to potentially be raised concurrently - but unless you have some shared state that you don't handle carefully, it should be fine. The results shouldn't get "corrupted" - if they do, that's definitely a bug in .NET.

Note that if you're using async calls, you probably don't need the worker threads - the whole point of doing things async is that you issue the call and then don't block a thread, so it's fine to do that from the UI thread (or whatever).

If you're able to use bleeding-edge technology, the async/await feature in C# 5 / .NET 4.5 (which is in Release Candidate mode) could make your life a lot easier.

answered Jun 18, 2012 at 18:49

Jon Skeet

1.5m893 gold badges9.3k silver badges9.3k bronze badges

Sign up to request clarification or add additional context in comments.

2 Comments

s. holton Over a year ago

Thanks to all 4 responders. My only reason to consider working treads was to possible "harness" multiple cpus as the load grows. And I wasn't sure if the "completion" routine executed under the thread of the async get, or "my" thread (if under async get thread, then I might need locks??)

Jon Skeet Over a year ago

By default I believe WebClient will rendezvous back with the synchronization context that starts it - but unless you're doing a lot of work with the response, I wouldn't expect that to be an issue.

Collectives™ on Stack Overflow

c# webclient async

1 Answer 1

2 Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

1 Answer 1

2 Comments

Your Answer

Sign up or log in

Post as a guest

Related