Asynchronous WebRequests using C#

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开发者_JAVA技巧). 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.)

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.

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);
                });
}

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

Use WebClient with Async methods.

Begin\End is more difficult to use.