public async Task Invoke(HttpContext context)
{
CapacityCheckResult checkResult = _capacityGuard.CheckCapacity(context.RequestAborted);
if (!checkResult.ExecutionAllowed)
{
EnqueueStatus enqueueStatus = await checkResult.QueueTask; // this is the place task waits in queue
// execution cancelled or queue timeout reached or queue full
if (enqueueStatus != EnqueueStatus.AllowExecution && !context.RequestAborted.IsCancellationRequested)
{
var responseFeature = context.Features.Get <IHttpResponseFeature>();
responseFeature.StatusCode = StatusCodes.Status429TooManyRequests;
responseFeature.ReasonPhrase = enqueueStatus.ToString();
return;
}
}
try
{
await _next(context);
}
finally
{
_capacityGuard.FinishExecution();
}
}
public CapacityCheckResult CheckCapacity(CancellationToken requestAbortedCancellationToken)
{
try
{
CancellationToken enqueueCancellationToken = GetEnqueueCancellationToken(requestAbortedCancellationToken);
_guardSemaphore.Wait(enqueueCancellationToken);
if (_concurrentRequestsCount < _throttlingConfiguration.ConcurrentRequestsLimit)
{
++_concurrentRequestsCount;
return(CapacityCheckResult.GetAllowed());
}
return(CapacityCheckResult.GetQueued(Enqueue(enqueueCancellationToken)));
}
catch (OperationCanceledException)
{
return(CapacityCheckResult.GetCancelled());
}
finally
{
_guardSemaphore.Release();
}
}