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I am using parallel.foreach in my code to submit multiple url for my application. Initially it work fine but after few day I noticed this exception occurs often. I googled it for many hours but no luck for me.

Explaination: We have Api SMS system from where client submit sms to us and we submit to operators for bulksms. I have 10 URL to submit to specific operator File stop after few seconds with this error. Exception message: One or more errors occurred.

Below is my piece of code.

 Parallel.ForEach(urlList,
    Sub(state, line, index)

      If urlList(index).Sender.ToString = "" Then
          urlList(index).response = "ignore"
      Else
          urlList(index).response = SendHttpRequest(state.url.ToString)
      End If

      urlList(index).url = state.url
    End Sub)

and below is other function which submit HTTP Request.

Public Function SendHttpRequest(ByVal url As String) As String
    Dim responsetext As String = ""
    Try
        Dim webR As WebRequest = HttpWebRequest.Create(url)
        webR.Timeout = 40000
        Dim WebResponse As HttpWebResponse = TryCast(webR.GetResponse(), HttpWebResponse)
        Dim stream As Stream = WebResponse.GetResponseStream()
        Dim reader As New StreamReader(stream)
        responsetext = reader.ReadToEnd()
    Catch ex As Exception
        responsetext = ex.ToString() & vbCrLf
    End Try
    Return responsetext
End Function
Improve this question
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  • 1
    It's a bit of a concern that you have spent several days on this and seem not to have worked out that an AggregateException has an InnerExceptions property that is a collection of all the exceptions it is aggregating. You're supposed to examine each exception in that collection to find out what actually happened. Commented Jan 29, 2019 at 9:53
  • Thank you for response. you mean I should apply try catch on parallel.foreach (first code) and handle inner exceptions. Commented Jan 29, 2019 at 11:57
  • 2
    Where you put an exception handler depends on where you want to handle the exception but I would suggest that it is wrong to return an exception message from a function that is supposed to return text received from a web request. That suggests that, as you said, you should put the Parallel.ForEach in a Try block, catch the AggregateException and then examine each item in its InnerExceptions collection. You can then retry just the ones that failed if appropriate or whatever else you like. Commented Jan 30, 2019 at 3:24
  • @jmcilhinneyThank for the suggestion. I did the same as you said and caught the innerexceptions. Now I can handle exceptions as I required. Thanks again. Commented Jan 30, 2019 at 8:10
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