IEnumerator <Task <AsyncCompletedEventArgs> > FetchOperationAsyncHelper(object state, CancellationToken token, int timeout, Action continuator)
{
var tcs = new TaskCompletionSource <AsyncCompletedEventArgs>();
// prepare the timeout
CancellationToken newToken;
if (timeout != Timeout.Infinite)
{
var cts = CancellationTokenSource.CreateLinkedTokenSource(token);
TaskExt.CancelAfterEx(cts, timeout * 1000);
newToken = cts.Token;
}
else
{
newToken = token;
}
/* handle completion */
AsyncCompletedEventHandler handler = (sender, args) =>
{
if (args.Cancelled)
{
tcs.TrySetCanceled();
}
else if (args.Error != null)
{
tcs.SetException(args.Error);
}
else
{
tcs.SetResult(args);
}
};
this.FetchOperationCompleted += handler;
try
{
using (newToken.Register(() =>
{
try
{
tcs.SetCanceled();
}
catch (InvalidOperationException)
{
/* cancel when already finished, does not matter */
#if DEBUG
Tracing.WarningDAL("Canceled async db operation, when it has already completed.");
#endif
}
}, useSynchronizationContext: false))
{
this.StartFetchOperation(state);
yield return(tcs.Task.Continuation(continuator));
}
}
finally
{
this.FetchOperationCompleted -= handler;
}
}