Asynchronous WebRequests using C#

Question

Hi i have a function that passes url Get parameters to a php file on a webserver and waits for a response from the file (normally takes 10-20 seconds). I want to put this inside a loop because I have to send these Get requests to about 5 different php files at once but when i try to add it to a loop the function makes the loop wait until the file returns the response before it will go on to the next one.

    public string HttpGet(string URI, string Parameters)
    {
        HttpWebRequest request = (HttpWebRequest)WebRequest.Create(URI + Parameters);

        HttpWebResponse response = (HttpWebResponse)request.GetResponse();
        StreamReader resStream = new StreamReader(response.GetResponseStream());
          return resStream.ReadToEnd().Trim();
    }

    private void SendCommand()
    {
        for( int i = 0; i <= 4; i++)
        {
            AddRTB(HttpGet(url, paramater));
        }
    }

Is there a way that i could send the all 5 requests at once without waiting for the previous to finish? (i was thinking about threading it but alas i never touched it before is i don't know where to start.)

Threading is the way to go for this, though you'll need to wait for all 5 to reply before continuing. — ChrisF
– ChrisF, Commented Sep 26, 2010 at 18:38

linuxuser27 · Accepted Answer · 2010-09-26 18:40:15Z

9

Instead of using the GetResponse() method you could use the BeginGetResponse() which is a non-blocking call. It takes a callback that can then handle the WebResponse object when it finally returns. The example in the link will give you a good idea of how to have the main thread wait for all the responses to return.

answered Sep 26, 2010 at 18:40

linuxuser27

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Scott Weinstein · Accepted Answer · 2010-09-26 21:45:12Z

9

Here are two approaches which uses the TPL.

The first waits for all the requests to complete before you access any of the results

var runningTasks = new List<Task<string>>();

for (int ii = 0; ii <= 4; ii++)
{
    var wreq = (HttpWebRequest)WebRequest.Create("..." + ii);

    var taskResp = Task.Factory.FromAsync<WebResponse>(wreq.BeginGetResponse, 
                                                    wreq.EndGetResponse, 
                                                    null);
    var taskResult = taskResp.ContinueWith(tsk => new StreamReader(tsk.Result.GetResponseStream()).ReadToEnd().Trim());
    runningTasks.Add(taskResult);
}

Task.WaitAll(runningTasks.ToArray());
IEnumerable<string> results = runningTasks.Select(tsk => tsk.Result);

and the second does something with each result as it comes in:

for (int ii = 0; ii <= 4; ii++)
{
    var wreq = (HttpWebRequest)WebRequest.Create("..." + ii);

    var taskResp = Task.Factory.FromAsync<WebResponse>(wreq.BeginGetResponse, 
                                                    wreq.EndGetResponse, 
                                                    null);
    taskResp.ContinueWith(tsk => new StreamReader(tsk.Result.GetResponseStream()).ReadToEnd().Trim())
            .ContinueWith((Task<string> trs) => 
                { 
                    var result = trs.Result;
                    DoSomthingWithTheResult(result);
                });
}

edited Sep 26, 2010 at 21:45

answered Sep 26, 2010 at 21:37

Scott Weinstein

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3 Comments

Arseni Mourzenko Over a year ago

+1. Even if @linuxuser27 answer has nothing wrong, this one answers better to the question and will be much easier to implement.

linuxuser27 Over a year ago

+1 Indeed it is. The ContinueWith() method is a good idea.

Konstantin Tarkus Over a year ago

And how would this change if I need to send some data with HTTP POST request with BeginGetRequestStream / EndGetRequestSteam ? stackoverflow.com/questions/4190903

Sandeep Singh Rawat · Accepted Answer · 2010-09-26 18:44:23Z

1

Instead of GetResponse use BeginGetResonse method of request class. Sample and documentation can be found at http://msdn.microsoft.com/en-us/library/system.net.httpwebrequest.begingetresponse.aspx

answered Sep 26, 2010 at 18:44

Sandeep Singh Rawat

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Comments

gandjustas · Accepted Answer · 2010-09-26 18:58:08Z

0

Use WebClient with Async methods.

Begin\End is more difficult to use.

answered Sep 26, 2010 at 18:58

gandjustas

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