Async HttpWebRequest


A

APA

I've seen the MS sample async web request pattern and I ask is it really async if it is using a ManualResetEvent and setting WaitOne()? The
ManualResetEvent object is being declared as a static variable so isn't it causing problems with other threads that may be using the same class to
execute the async web request? If I remove the ManualResetEvent object will it be truly asynchronous and will I be losing something? Also, in my app
the web request is posting data.

For those that haven't seen the code it looks something like this:


public class AsyncWebRequest

public AsyncWebRequest(){}

public static ManualResetEvent allDone = new ManualResetEvent(false);

const int BUFFER_SIZE = 1024;

public void WebReq(string URL, string somedata)
{
try
{

if (URL.Trim() != "")
{
byte[] data = Encoding.ASCII.GetBytes(somedata);

HttpWebRequest webRequest = (HttpWebRequest)System.Net.WebRequest.Create(URL);
webRequest.Method = "POST";
webRequest.ContentType = "application/x-www-form-urlencoded";
webRequest.ContentLength = data.Length;

ManualResetEvent WaitHndle = new ManualResetEvent(false);
RequestState rs = new RequestState(WaitHndle,this.Debug);

rs.Request = webRequest;
rs.DataToSend = data;

webRequest.BeginGetRequestStream(new AsyncCallback(ReadCallbackRequest), rs);

IAsyncResult r = (IAsyncResult)webRequest.BeginGetResponse(new AsyncCallback(RespCallback), rs);

ThreadPool.RegisterWaitForSingleObject(r.AsyncWaitHandle, new WaitOrTimerCallback(ScanTimeoutCallback), rs, (30 * 1000), true);

allDone.WaitOne();
rs.ResponseStream.Close();

}
}
catch (WebException ex) { string str = ex.ToString(); }
catch (Exception ex) { string sr = ex.ToString(); }
}


private static void RespCallback(IAsyncResult ar)
{
RequestState rs = (RequestState)ar.AsyncState;
try
{
WebRequest req = rs.Request;

WebResponse resp = req.EndGetResponse(ar);

Stream ResponseStream = resp.GetResponseStream();

rs.ResponseStream = ResponseStream;
rs.Waitone.Set();

if (rs.Debug)
{
IAsyncResult iarRead = ResponseStream.BeginRead(rs.BufferRead, 0, BUFFER_SIZE, new AsyncCallback(ReadCallBack), rs);
}
}
catch (Exception ex)
{
rs.Waitone.Set();
}
}


private static void ReadCallbackRequest(IAsyncResult asynchronousResult)
{
RequestState rs = (RequestState)asynchronousResult.AsyncState;
try
{
HttpWebRequest request = rs.Request;

Stream postStream = request.EndGetRequestStream(asynchronousResult);

postStream.Write(rs.DataToSend, 0, rs.DataToSend.Length);
postStream.Close();
}
catch (Exception ex)
{
}
allDone.Set();

}

private static void ScanTimeoutCallback(object state, bool timedOut)
{
if (timedOut)
{
RequestState reqState = (RequestState)state;
if (reqState != null)
reqState.Request.Abort();
}
}

public class RequestState
{
const int BufferSize = 1024;
public byte[] DataToSend;
public StringBuilder RequestData;
public byte[] BufferRead;
public HttpWebRequest Request;
public Stream ResponseStream;
public ManualResetEvent Waitone;
public bool Debug;

public Decoder StreamDecode = Encoding.UTF8.GetDecoder();

public RequestState(ManualResetEvent waitHandle,bool debug)
{
BufferRead = new byte[BufferSize];
RequestData = new StringBuilder(String.Empty);
Request = null;
ResponseStream = null;
Waitone = waitHandle;
Debug = debug;
}
}
}
 
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B

bruce barker

normally you would put code you want to happen during the async request
before the wait. then after the wait, you put the code to handle the response.

the question is what do you want the thread to do during the request call?
after?

note: this code will not work from an asp.net application. if a webform, use
the builting async processing, if called from a web service, you will want to
use a WaitHandle rather than ManualResetEvent.

-- bruce (sqlwork.com)


APA said:
I've seen the MS sample async web request pattern and I ask is it really async if it is using a ManualResetEvent and setting WaitOne()? The
ManualResetEvent object is being declared as a static variable so isn't it causing problems with other threads that may be using the same class to
execute the async web request? If I remove the ManualResetEvent object will it be truly asynchronous and will I be losing something? Also, in my app
the web request is posting data.

For those that haven't seen the code it looks something like this:


public class AsyncWebRequest

public AsyncWebRequest(){}

public static ManualResetEvent allDone = new ManualResetEvent(false);

const int BUFFER_SIZE = 1024;

public void WebReq(string URL, string somedata)
{
try
{

if (URL.Trim() != "")
{
byte[] data = Encoding.ASCII.GetBytes(somedata);

HttpWebRequest webRequest = (HttpWebRequest)System.Net.WebRequest.Create(URL);
webRequest.Method = "POST";
webRequest.ContentType = "application/x-www-form-urlencoded";
webRequest.ContentLength = data.Length;

ManualResetEvent WaitHndle = new ManualResetEvent(false);
RequestState rs = new RequestState(WaitHndle,this.Debug);

rs.Request = webRequest;
rs.DataToSend = data;

webRequest.BeginGetRequestStream(new AsyncCallback(ReadCallbackRequest), rs);

IAsyncResult r = (IAsyncResult)webRequest.BeginGetResponse(new AsyncCallback(RespCallback), rs);

ThreadPool.RegisterWaitForSingleObject(r.AsyncWaitHandle, new WaitOrTimerCallback(ScanTimeoutCallback), rs, (30 * 1000), true);

allDone.WaitOne();
rs.ResponseStream.Close();

}
}
catch (WebException ex) { string str = ex.ToString(); }
catch (Exception ex) { string sr = ex.ToString(); }
}


private static void RespCallback(IAsyncResult ar)
{
RequestState rs = (RequestState)ar.AsyncState;
try
{
WebRequest req = rs.Request;

WebResponse resp = req.EndGetResponse(ar);

Stream ResponseStream = resp.GetResponseStream();

rs.ResponseStream = ResponseStream;
rs.Waitone.Set();

if (rs.Debug)
{
IAsyncResult iarRead = ResponseStream.BeginRead(rs.BufferRead, 0, BUFFER_SIZE, new AsyncCallback(ReadCallBack), rs);
}
}
catch (Exception ex)
{
rs.Waitone.Set();
}
}


private static void ReadCallbackRequest(IAsyncResult asynchronousResult)
{
RequestState rs = (RequestState)asynchronousResult.AsyncState;
try
{
HttpWebRequest request = rs.Request;

Stream postStream = request.EndGetRequestStream(asynchronousResult);

postStream.Write(rs.DataToSend, 0, rs.DataToSend.Length);
postStream.Close();
}
catch (Exception ex)
{
}
allDone.Set();

}

private static void ScanTimeoutCallback(object state, bool timedOut)
{
if (timedOut)
{
RequestState reqState = (RequestState)state;
if (reqState != null)
reqState.Request.Abort();
}
}

public class RequestState
{
const int BufferSize = 1024;
public byte[] DataToSend;
public StringBuilder RequestData;
public byte[] BufferRead;
public HttpWebRequest Request;
public Stream ResponseStream;
public ManualResetEvent Waitone;
public bool Debug;

public Decoder StreamDecode = Encoding.UTF8.GetDecoder();

public RequestState(ManualResetEvent waitHandle,bool debug)
{
BufferRead = new byte[BufferSize];
RequestData = new StringBuilder(String.Empty);
Request = null;
ResponseStream = null;
Waitone = waitHandle;
Debug = debug;
}
}
}
 

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