I must be doing something wrong since this code is blocking and runs synchronously, inspite of calling the async method of GetStringAsync. Any help would really help me understand the reasons:
Private Async Sub btnTest_Click(sender As Object, e As EventArgs) Handles btnTest.Click
Dim urls As List(Of String) = SetUpURLList()
Dim baseAddress = New Uri("http://www.amazon.com")
ServicePointManager.DefaultConnectionLimit = 10
Dim requestNumber As Integer = 0
For Each url In urls
requestNumber += 1
Console.WriteLine("Request #:{0}", requestNumber)
Dim cookies As New CookieContainer()
Dim handler As New HttpClientHandler With {.CookieContainer = cookies, _
.UseCookies = True}
Dim httpClient = New HttpClient(handler) With {.BaseAddress = baseAddress}
Dim response As String = Await HttpClient.GetStringAsync(url).ConfigureAwait(False)
For Each cook As Cookie In cookies.GetCookies(baseAddress)
Console.WriteLine(cook.Name & "=" & cook.Value)
Next
httpClient.Dispose()
Next
Console.WriteLine("Done")
End Sub
Your code isn't blocking, it's just sequential. You are firing each Async operation and asynchronously waiting for it to complete with Await before starting the next one.
If you want to fire all these operations concurrently first create a task for each url and then Await all these tasks at once using Task.WhenAll:
Dim semaphore As New SemaphoreSlim(10)
Async Sub btnTest_Click(sender As Object, e As EventArgs) Handles btnTest.Click
Dim urls As List(Of String) = SetUpURLList()
ServicePointManager.DefaultConnectionLimit = 10
Dim tasks As List(Of Task) = new List(Of Task)()
For Each url In urls
tasks.Add(GetUrlAsync(url))
Next
Await Task.WhenAll(tasks)
Console.WriteLine("Done")
End Sub
Async Function GetUrlAsync(url As String) As Task
Await semaphore.WaitAsync()
Dim baseAddress = New Uri("http://www.amazon.com")
Dim cookies As New CookieContainer()
Dim handler As New HttpClientHandler With {.CookieContainer = cookies, _
.UseCookies = True}
Dim httpClient = New HttpClient(handler) With {.BaseAddress = baseAddress}
Dim response As String = Await HttpClient.GetStringAsync(url).ConfigureAwait(False)
For Each cook As Cookie In cookies.GetCookies(baseAddress)
Console.WriteLine(cook.Name & "=" & cook.Value)
Next
httpClient.Dispose()
semaphore.Release()
End Sub
*I hope this code makes sense, since I'm not really familiar with VB.Net.
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