Fixed MessageQueue race condition

src/Discord.Net/Net/Rest/RequestQueue/RequestQueueBucket.cs

@@ -16,8 +16,8 @@ namespace Discord.Net.Rest
         private readonly ConcurrentQueue<RestRequest> _queue;
         private readonly SemaphoreSlim _lock;
         private Task _resetTask;
-        private DateTime? _retryAfter;
-        private bool _waitingToProcess;
+        private bool _waitingToProcess, _destroyed; //TODO: Remove _destroyed
+        private int _id;
 
         public int WindowMaxCount { get; }
         public int WindowSeconds { get; }
@@ -44,10 +44,12 @@ namespace Discord.Net.Rest
             WindowSeconds = windowSeconds;
             _queue = new ConcurrentQueue<RestRequest>();
             _lock = new SemaphoreSlim(1, 1);
+            _id = new System.Random().Next(0, int.MaxValue);
         }
 
         public void Queue(RestRequest request)
         {
+            if (_destroyed) throw new Exception();
             //Assume this obj's parent is under lock
 
             _queue.Enqueue(request);
@@ -75,7 +77,7 @@ namespace Discord.Net.Rest
                     //If we're waiting to reset (due to a rate limit exception, or preemptive check), abort
                     if (WindowCount == WindowMaxCount) return;
                     //Get next request, return if queue is empty
-                    if (!_queue.TryPeek(out request)) return;
+                    if (!_queue.TryPeek(out request)) break;
 
                     try
                     {
@@ -88,17 +90,20 @@ namespace Discord.Net.Rest
                     }
                     catch (HttpRateLimitException ex) //Preemptive check failed, use Discord's time instead of our own
                     {
-                        if (_resetTask == null)
+                        WindowCount = WindowMaxCount;
+                        var task = _resetTask;
+                        if (task != null)
                         {
-                            //No reset has been queued yet, lets create one as if this *was* preemptive
-                            _resetTask = ResetAfter(ex.RetryAfterMilliseconds);
-                            Debug($"External rate limit: Reset in {ex.RetryAfterMilliseconds} ms");
+                            Debug($"External rate limit: Extended to {ex.RetryAfterMilliseconds} ms");
+                            var retryAfter = DateTime.UtcNow.AddMilliseconds(ex.RetryAfterMilliseconds);
+                            await task.ConfigureAwait(false);
+                            int millis = (int)Math.Ceiling((DateTime.UtcNow - retryAfter).TotalMilliseconds);
+                            _resetTask = ResetAfter(millis);
                         }
                         else
                         {
-                            //A preemptive reset is already queued, set RetryAfter to extend it
-                            _retryAfter = DateTime.UtcNow.AddMilliseconds(ex.RetryAfterMilliseconds);
-                            Debug($"External rate limit: Extended to {ex.RetryAfterMilliseconds} ms");
+                            Debug($"External rate limit: Reset in {ex.RetryAfterMilliseconds} ms");
+                            _resetTask = ResetAfter(ex.RetryAfterMilliseconds);
                         }
                         return;
                     }
@@ -132,6 +137,25 @@ namespace Discord.Net.Rest
                         Debug($"Internal rate limit: Reset in {WindowSeconds * 1000} ms");
                     }
                 }
+
+                //If queue is empty, non-global, and there is no active rate limit, remove this bucket
+                if (_resetTask == null && _bucketGroup == BucketGroup.Guild)
+                {
+                    try
+                    {
+                        await _parent.Lock().ConfigureAwait(false);
+                        if (_queue.IsEmpty) //Double check, in case a request was queued before we got both locks
+                        {
+                            Debug($"Destroy");
+                            _parent.DestroyGuildBucket((GuildBucket)_bucketId, _guildId);
+                            _destroyed = true;
+                        }
+                    }
+                    finally
+                    {
+                        _parent.Unlock();
+                    }
+                }
             }
             finally
             {
@@ -155,36 +179,14 @@ namespace Discord.Net.Rest
             {
                 await Lock().ConfigureAwait(false);
 
-                //If an extension has been planned, start a new wait task
-                if (_retryAfter != null)
-                {
-                    _resetTask = ResetAfter((int)(_retryAfter.Value - DateTime.UtcNow).TotalMilliseconds);
-                    _retryAfter = null;
-                    return;
-                }
-
                 Debug($"Reset");
+
                 //Reset the current window count and set our state back to normal
                 WindowCount = 0;
                 _resetTask = null;
 
                 //Wait is over, work through the current queue
                 await ProcessQueue().ConfigureAwait(false);
-                
-                //If queue is empty and non-global, remove this bucket
-                if (_bucketGroup == BucketGroup.Guild && _queue.IsEmpty)
-                {
-                    try
-                    {
-                        await _parent.Lock().ConfigureAwait(false);
-                        if (_queue.IsEmpty) //Double check, in case a request was queued before we got both locks
-                            _parent.DestroyGuildBucket((GuildBucket)_bucketId, _guildId);
-                    }
-                    finally
-                    {
-                        _parent.Unlock();
-                    }
-                }
             }
             finally
             {
@@ -217,7 +219,7 @@ namespace Discord.Net.Rest
                     name = "Unknown";
                     break;
             }
-            System.Diagnostics.Debug.WriteLine($"[{name}] {text}");
+            System.Diagnostics.Debug.WriteLine($"[{name} {_id}] {text}");
         }
     }
 }