I have a strange problem in my MVC 4.0 application. I use REST web services (Amazon Associate) . I created a method, which I use from everywhere. The shortened version is this:
private async Task<XElement> GetRequest(string url)
{
string myresponse;
HttpResponseMessage response = null;
HttpClient client = new HttpClient();
try
{
response = await client.GetAsync(url);
myresponse = response.Content.ToString();
if (myresponse.Contains("503"))
{
myTrace.WriteLine("503 Sleep.....");
Thread.Sleep(3000); // looks like amazon us does not like fast requests....
return await GetRequest(url); //restart after pausing....
}
}
catch (TaskCanceledException ex)
{
myTrace.WriteLine("TaskCancelled From GetRequest: " + ex);
return null;
}
catch (HttpRequestException ex)
{
myTrace.WriteLine("RequestException Sleep.....");
Thread.Sleep(300000); // 5 minutes de pause
}
catch (Exception ex)
{
myTrace.WriteLine("From GetRequest: " + ex);
return null;
}
try
{
XElement content = await response.Content.ReadAsAsync<XElement>();
response.Dispose();
client.Dispose();
return content;
}
catch (Exception)
{
return null;
}
}
Nothing fancy, it does work perfectly well....But, now, on a specific call, it bombs on client.GetAsync(url)
. At first I suspected something in the url to be wrong, so I grabbed it from a debugger session and pasted it directly in my browser, got the expected answer...
So, nothing wrong with the URL. Made a little Unit Test, works just fine with that same specific URL...
As it bombs in the debugger, difficult to see what's wrong. (There are no exceptions thrown!). Finally, I saw with IntelliTrace that there ARE exceptions, seemingly inside System.Threading.Tasks
. Difficult to pin point, as the call Stack is a bit confusing for my NON expert eyes....
Here is the call stack I get from a previous pass in the code:
> System.Web.dll!System.Web.ThreadContext.AssociateWithCurrentThread(bool setImpersonationContext = {unknown}) C#
System.Web.dll!System.Web.HttpApplication.OnThreadEnterPrivate(bool setImpersonationContext = {unknown}) C#
System.Web.dll!System.Web.HttpApplication.OnThreadEnter() C#
System.Web.dll!System.Web.HttpApplication.System.Web.Util.ISyncContext.Enter() C#
System.Web.dll!System.Web.Util.SynchronizationHelper.SafeWrapCallback(System.Action action = {unknown}) C#
System.Web.dll!<>c__DisplayClass9.AnonymousMethod(System.Threading.Tasks.Task _ = {unknown}) C#
mscorlib.dll!System.Threading.Tasks.ContinuationTaskFromTask.InnerInvoke() C#
mscorlib.dll!System.Threading.Tasks.Task.Execute() C#
mscorlib.dll!System.Threading.Tasks.Task.ExecutionContextCallback(object obj = {unknown}) C#
mscorlib.dll!System.Threading.ExecutionContext.RunInternal(System.Threading.ExecutionContext executionContext = {unknown}, System.Threading.ContextCallback callback = {unknown}, object state = {unknown}, bool preserveSyncCtx = {unknown}) C#
mscorlib.dll!System.Threading.ExecutionContext.Run(System.Threading.ExecutionContext executionContext = {unknown}, System.Threading.ContextCallback callback = {unknown}, object state = {unknown}, bool preserveSyncCtx = {unknown}) C#
mscorlib.dll!System.Threading.Tasks.Task.ExecuteWithThreadLocal(ref System.Threading.Tasks.Task currentTaskSlot = {unknown}) C#
mscorlib.dll!System.Threading.Tasks.Task.ExecuteEntry(bool bPreventDoubleExecution = {unknown}) C#
mscorlib.dll!System.Threading.Tasks.Task.System.Threading.IThreadPoolWorkItem.ExecuteWorkItem() C#
mscorlib.dll!System.Threading.ThreadPoolWorkQueue.Dispatch() C#
mscorlib.dll!System.Threading._ThreadPoolWaitCallback.PerformWaitCallback() C#
Anyway, this looks definitely linked to Tasks, Async, Background workers, etc... Is there a good way to "clear" all other running tasks, to avoid this problem?
Thanks for your help,
Bernard.
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