Hi there,
for use on vanilla Windows7 systems (.Net 4.0) I still use my own Http Library, which is built around the Httpwebrequest and includes synchronchronous and asynchronous functions for different mime-types, as well as JSON and XML support.
By now I use .BeginGetRequest and .BegitGetResponse for the async calls, but extending the library blows up the code and makes it more and more complex. As an alternative I have considered wrapping the existing sync versions transparently
into a delegate wrapper and executing it on a threadpool thread (example below).
As I see it, advantages would be:
- simpler exception handling (around .endinvoke)
- more transparent and failsafe code
- simple implementation of Timeout and ReadTimeout (which is a bit of a pain in the async version)
- requests are created on the threadpool thread as well (slight ramp up)
Question: can you suggest any disadvantages going this way (performance, scaling, resources) ? Or a better way of doing it ?
A potential issue might be, that I am blocking a full threadpool thread, instead of using IO/blocking mechanisms.
Any answers / explanations / references for further reading would be greatly appreciated.
And yes, I'm using the Httpclient for the .Net 4.5 framework
Code examples:
''' <summary>Executes as synchronous GET request and returns string result</summary>
Public Function GetSync(url As String) As String
' create GET request
Dim request = DirectCast(Net.WebRequest.Create(url), HttpWebRequest)
request.Method = "GET"
' fetch result
Dim response = DirectCast(request.GetResponse(), HttpWebResponse)
Using responsestream = response.GetResponseStream, reader = New IO.StreamReader(responsestream)
Return reader.ReadToEnd()
End Using
End Function
''' <summary>Executes an async GET request and directs result to user defined callback</summary>
Public Sub GetAsync(url As String, resultCallback As Action(Of String))
' create GET request
Dim request = DirectCast(Net.WebRequest.Create(url), HttpWebRequest)
request.Method = "GET"
' send async request
request.BeginGetResponse(New AsyncCallback( _
Sub(iar As IAsyncResult)
'Dim result = DirectCast(iar.AsyncState, AsyncResult)
Using webResponse As HttpWebResponse = DirectCast(request.EndGetResponse(iar), HttpWebResponse), _
responsestream = webResponse.GetResponseStream, reader = New IO.StreamReader(responsestream)
resultCallback(reader.ReadToEnd())
End Using
End Sub), Nothing)
End Sub
''' <summary>Executes a synchronous GET request on a threadpool thread and directs result to user defined callback</summary>
Public Sub GetAsyncWrapped(url As String, resultCallback As Action(Of String))
' define wrapper delegate
Dim worker = New Action( _
Sub()
Dim request = DirectCast(Net.WebRequest.Create(url), HttpWebRequest)
request.Method = "GET"
resultCallback(GetSync(url))
End Sub)
' run it async on a threadpool thread
worker.BeginInvoke(New AsyncCallback( _
Sub(iar As IAsyncResult)
worker.EndInvoke(DirectCast(iar, AsyncResult))
End Sub), Nothing)
End Sub
To explain the question I used simple versions with lambda expressions.
