I need to use Async/Await in my already running program to make it faster - vb.net

Question

I am having a program in VB, which searches for image in a website as follows:
www.website.com/1.jpg | www.website.com/2.jpg | www.website.com/3.jpg
in loop, and the program opens up only 3.jpg in browser, since 1 and 2 jpg does not exit in server. The program is up and running, but is very very slow, around 120 searches in a minute. However one of my colleagues designed the same program in Angular and that program is running very fast, around 500/600 searches in a minute.
He told me, what he did is generated 50 asynchronous calls to server, and then again 50, and then again 50 and went on like this. thus making his program very fast and ovbiously accurate.
I studied and learnt, that in Visual Basic too, we have async and wait calls to server request, but I cannot figure out how.
Here goes my existing code. Can anyone help me.
Private Sub Button2_Click(sender As Object, e As EventArgs) Handles Button2.Click
Dim MYURL as string
itemsF = 0
While Not itemsF = 50000
MYURL = "www.website.com/" & itemsF & ".jpg"
CheckPageExists(MYURL)
itemsF=itemsF+1
End While
End Sub
Private Function CheckPageExists(ByVal url As String) As Boolean
Dim request As Net.HttpWebRequest
Dim response As Net.HttpWebResponse
request = Net.WebRequest.Create(url)
request.Timeout = 5000
Try
response = request.GetResponse()
Catch ex As Exception
'IMAGE DOES NOT EXITS
Exit Function
End Try
Process.Start(url)
End Function

Answer 1

First, you have to make CheckPageExists an Async method:
Private Async Function CheckPageExists(ByVal url As String) As Task(Of Boolean)
Dim request As Net.HttpWebRequest = Net.WebRequest.Create(url)
request.Timeout = 5
Dim Result As Boolean
Try
Using response As HttpWebResponse = Await request.GetResponseAsync.ConfigureAwait(False)
Using responseReader As New IO.StreamReader(response.GetResponseStream)
Dim actualResponse As String = Await responseReader.ReadToEndAsync
Result = True
End Using
End Using
Catch ex As Exception
'IMAGE DOES NOT EXITS
Result = False
End Try
Console.WriteLine(url)
''Process.Start("chrome.exe", url)
Return Result
End Function
As you can see, instead of GetResponse we are using GetResponseAsync, which is Async itself. This method is very similar to what you were doing before, I
just added Return statements for clarity and a StreamReader to read the response of your website.
Once you've done that, you just need to change your Button2_Click method to call this other method, which incorporates all you were doing before:
Async Function MakeRequests() As Task
Dim tasks As List(Of Task(Of Boolean)) = New List(Of Task(Of Boolean))
Dim itemsF As Integer = 5
For i = 1 To itemsF
Dim MYURL As String = "http://www.touchegolfschool.com/images/" & i & ".jpg"
tasks.Add(CheckPageExists(MYURL))
Next
While tasks.Select(Function(x) x.Result).Count < tasks.Count
Thread.Sleep(100)
End While
End Function
The main change was adding tasks.Select(Function(x) x.Result).Count < tasks.Count; what you were seeing before was a request made but never returning because of the time it took to return; telling the main function to wait until all requests have a result makes the application wait long enough for the responses to come.
Here the main difference is the use of Tasks.
Check this for official documentation on asynchronous programming.