fix: queue gauge metric

Makefile

@@ -5,3 +5,6 @@ sample:
 
 sample-clean:
 	@docker compose -f docker-compose.sample.yaml down
+
+benchmark:
+	dotnet run -c Release --project ./tests/benchmark/Farfetch.LoadShedding.BenchmarkTests/Farfetch.LoadShedding.BenchmarkTests.csproj

src/Farfetch.LoadShedding/Events/Args/ItemDequeuedEventArgs.cs

@@ -6,29 +6,17 @@ namespace Farfetch.LoadShedding.Events.Args
     /// <summary>
     /// Event args for the task dequeued event.
     /// </summary>
-    public class ItemDequeuedEventArgs : ItemEventArgs
+    public class ItemDequeuedEventArgs : TaskQueueEventArgs
     {
-        internal ItemDequeuedEventArgs(Priority priority, TimeSpan queueTime, int queueLimit, int queueCount)
-            : base(priority)
+        internal ItemDequeuedEventArgs(Priority priority, TimeSpan queueTime, IReadOnlyCounter queueCounter)
+            : base(priority, queueCounter)
         {
             this.QueueTime = queueTime;
-            this.QueueLimit = queueLimit;
-            this.QueueCount = queueCount;
         }
 
         /// <summary>
         /// Gets the time waiting in the queue.
         /// </summary>
         public TimeSpan QueueTime { get; }
-
-        /// <summary>
-        /// Gets the maximum number of items in the queue.
-        /// </summary>
-        public int QueueLimit { get; }
-
-        /// <summary>
-        /// Gets the current number of items in the queue.
-        /// </summary>
-        public int QueueCount { get; }
     }
 }

src/Farfetch.LoadShedding/Events/Args/ItemEnqueuedEventArgs.cs

@@ -5,23 +5,11 @@ namespace Farfetch.LoadShedding.Events.Args
     /// <summary>
     /// Event args for the task enqueued event.
     /// </summary>
-    public class ItemEnqueuedEventArgs : ItemEventArgs
+    public class ItemEnqueuedEventArgs : TaskQueueEventArgs
     {
-        internal ItemEnqueuedEventArgs(Priority priority, int queueLimit, int queueCount)
-            : base(priority)
+        internal ItemEnqueuedEventArgs(Priority priority, IReadOnlyCounter queueCounter)
+            : base(priority, queueCounter)
         {
-            this.QueueLimit = queueLimit;
-            this.QueueCount = queueCount;
         }
-
-        /// <summary>
-        /// Gets the maximum number of items in the queue.
-        /// </summary>
-        public int QueueLimit { get; }
-
-        /// <summary>
-        /// Gets the current number of items in the queue.
-        /// </summary>
-        public int QueueCount { get; }
     }
 }

src/Farfetch.LoadShedding/Events/Args/ItemProcessedEventArgs.cs

@@ -1,34 +1,22 @@
-using System;
+using System;
 using Farfetch.LoadShedding.Tasks;
 
 namespace Farfetch.LoadShedding.Events.Args
 {
     /// <summary>
     /// Event args for task processed event.
     /// </summary>
-    public class ItemProcessedEventArgs : ItemEventArgs
+    public class ItemProcessedEventArgs : TaskItemEventArgs
     {
-        internal ItemProcessedEventArgs(Priority priority, TimeSpan processingTime, int concurrencyLimit, int concurrencyCount)
-            : base(priority)
+        internal ItemProcessedEventArgs(Priority priority, TimeSpan processingTime, IReadOnlyCounter concurrencyCounter)
+            : base(priority, concurrencyCounter)
         {
             this.ProcessingTime = processingTime;
-            this.ConcurrencyLimit = concurrencyLimit;
-            this.ConcurrencyCount = concurrencyCount;
         }
 
         /// <summary>
         /// Gets time spent to process the task.
         /// </summary>
         public TimeSpan ProcessingTime { get; }
-
-        /// <summary>
-        /// Gets the current concurrency limit.
-        /// </summary>
-        public int ConcurrencyLimit { get; }
-
-        /// <summary>
-        /// Gets the current concurrency items count.
-        /// </summary>
-        public int ConcurrencyCount { get; }
     }
 }

src/Farfetch.LoadShedding/Events/Args/ItemProcessingEventArgs.cs

@@ -1,27 +1,15 @@
-using Farfetch.LoadShedding.Tasks;
+using Farfetch.LoadShedding.Tasks;
 
 namespace Farfetch.LoadShedding.Events.Args
 {
     /// <summary>
-    /// Event args for task procssing event.
+    /// Event args for task processing event.
     /// </summary>
-    public class ItemProcessingEventArgs : ItemEventArgs
+    public class ItemProcessingEventArgs : TaskItemEventArgs
     {
-        internal ItemProcessingEventArgs(Priority priority, int concurrencyLimit, int concurrencyCount)
-            : base(priority)
+        internal ItemProcessingEventArgs(Priority priority, IReadOnlyCounter concurrencyCounter)
+            : base(priority, concurrencyCounter)
         {
-            this.ConcurrencyLimit = concurrencyLimit;
-            this.ConcurrencyCount = concurrencyCount;
         }
-
-        /// <summary>
-        /// Gets the current concurrency limit.
-        /// </summary>
-        public int ConcurrencyLimit { get; }
-
-        /// <summary>
-        /// Gets the current concurrency items count.
-        /// </summary>
-        public int ConcurrencyCount { get; }
     }
 }

src/Farfetch.LoadShedding/Events/Args/TaskItemEventArgs.cs

@@ -0,0 +1,28 @@
+using Farfetch.LoadShedding.Tasks;
+
+namespace Farfetch.LoadShedding.Events.Args
+{
+    /// <summary>
+    /// Event args for task item event.
+    /// </summary>
+    public class TaskItemEventArgs : ItemEventArgs
+    {
+        private readonly IReadOnlyCounter _concurrencyCounter;
+
+        internal TaskItemEventArgs(Priority priority, IReadOnlyCounter concurrencyCounter)
+            : base(priority)
+        {
+            _concurrencyCounter = concurrencyCounter;
+        }
+
+        /// <summary>
+        /// Gets the current concurrency limit.
+        /// </summary>
+        public int ConcurrencyLimit => _concurrencyCounter.Limit;
+
+        /// <summary>
+        /// Gets the current concurrency items count.
+        /// </summary>
+        public int ConcurrencyCount => _concurrencyCounter.Count;
+    }
+}

src/Farfetch.LoadShedding/Events/Args/TaskQueueEventArgs.cs

@@ -0,0 +1,28 @@
+using Farfetch.LoadShedding.Tasks;
+
+namespace Farfetch.LoadShedding.Events.Args
+{
+    /// <summary>
+    /// Event args for the task queue event.
+    /// </summary>
+    public class TaskQueueEventArgs : ItemEventArgs
+    {
+        private readonly IReadOnlyCounter _queueCounter;
+
+        internal TaskQueueEventArgs(Priority priority, IReadOnlyCounter queueCounter)
+            : base(priority)
+        {
+            this._queueCounter = queueCounter;
+        }
+
+        /// <summary>
+        /// Gets the maximum number of items in the queue.
+        /// </summary>
+        public int QueueLimit => _queueCounter.Limit;
+
+        /// <summary>
+        /// Gets the current number of items in the queue.
+        /// </summary>
+        public int QueueCount => _queueCounter.Count;
+    }
+}

src/Farfetch.LoadShedding/Tasks/ConcurrentCounter.cs

@@ -1,8 +1,8 @@
 namespace Farfetch.LoadShedding.Tasks
 {
-    internal class ConcurrentCounter
+    internal class ConcurrentCounter : IReadOnlyCounter
     {
-        private readonly object _locker = new object();
+        private readonly object _locker = new();
 
         private int _count = 0;
 

src/Farfetch.LoadShedding/Tasks/IReadOnlyCounter.cs

@@ -0,0 +1,9 @@
+namespace Farfetch.LoadShedding.Tasks
+{
+    internal interface IReadOnlyCounter
+    {
+        int Count { get; }
+
+        int Limit { get; }
+    }
+}

src/Farfetch.LoadShedding/Tasks/Priority.cs

@@ -6,17 +6,17 @@ namespace Farfetch.LoadShedding.Tasks
     public enum Priority
     {
         /// <summary>
-        /// Priority as critical.
+        /// Priority as Critical.
         /// </summary>
         Critical = 0,
 
         /// <summary>
-        /// Priority as normal.
+        /// Priority as Normal.
         /// </summary>
         Normal = 1,
 
         /// <summary>
-        /// Priority as critical.
+        /// Priority as Non Critical.
         /// </summary>
         NonCritical = 2,
     }

src/Farfetch.LoadShedding/Tasks/TaskManager.cs

@@ -1,4 +1,4 @@
-using System;
+using System;
 using System.Threading;
 using System.Threading.Tasks;
 using Farfetch.LoadShedding.Constants;
@@ -12,7 +12,7 @@ internal class TaskManager : ITaskManager
     {
         private readonly TaskQueue _taskQueue;
 
-        private readonly ConcurrentCounter _counter = new ConcurrentCounter();
+        private readonly ConcurrentCounter _counter = new();
 
         private readonly int _queueTimeout;
         private readonly ILoadSheddingEvents _events;
@@ -30,8 +30,8 @@ public TaskManager(
 
             this._taskQueue = new TaskQueue(maxQueueSize)
             {
-                OnItemEnqueued = (count, item) => this.NotifyItemEnqueued(count, item),
-                OnItemDequeued = (count, item) => this.NotifyItemDequeued(count, item),
+                OnItemEnqueued = this.NotifyItemEnqueued,
+                OnItemDequeued = this.NotifyItemDequeued,
             };
 
             this._events?.ConcurrencyLimitChanged?.Raise(new LimitChangedEventArgs(this._counter.Limit));
@@ -86,11 +86,11 @@ public async Task<TaskItem> AcquireAsync(Priority priority, CancellationToken ca
         {
             var item = this.CreateTask(priority);
 
-            if (this._counter.TryIncrement(out var currentCount))
+            if (this._counter.TryIncrement(out var _))
             {
                 item.Process();
 
-                this.NotifyItemProcessing(item, currentCount);
+                this.NotifyItemProcessing(item);
 
                 return item;
             }
@@ -124,7 +124,8 @@ await item
                     break;
             }
 
-            this.NotifyItemProcessing(item, this._counter.Increment());
+            this._counter.Increment();
+            this.NotifyItemProcessing(item);
 
             return item;
         }
@@ -136,10 +137,9 @@ private TaskItem CreateTask(Priority priority)
             item.OnCompleted = () =>
             {
                 var count = this._counter.Decrement();
-
                 var processNext = count < this._counter.Limit;
 
-                this.NotifyItemProcessed(item, count);
+                this.NotifyItemProcessed(item);
 
                 if (processNext)
                 {
@@ -155,32 +155,28 @@ private void NotifyItemRejected(TaskItem item, string reason)
                 item.Priority,
                 reason));
 
-        private void NotifyItemProcessed(TaskItem item, int count)
+        private void NotifyItemProcessed(TaskItem item)
             => this._events?.ItemProcessed?.Raise(new ItemProcessedEventArgs(
                 item.Priority,
                 item.ProcessingTime,
-                this.ConcurrencyLimit,
-                count));
+                this._counter));
 
-        private void NotifyItemProcessing(TaskItem item, int count)
+        private void NotifyItemProcessing(TaskItem item)
             => this._events?.ItemProcessing?.Raise(new ItemProcessingEventArgs(
                 item.Priority,
-                this.ConcurrencyLimit,
-                count));
+                this._counter));
 
         private void NotifyConcurrencyLimitChanged()
             => this._events?.ConcurrencyLimitChanged?.Raise(new LimitChangedEventArgs(this._counter.Limit));
 
-        private void NotifyItemDequeued(int count, TaskItem item) => this._events?.ItemDequeued?.Raise(new ItemDequeuedEventArgs(
+        private void NotifyItemDequeued(TaskItem item) => this._events?.ItemDequeued?.Raise(new ItemDequeuedEventArgs(
              item.Priority,
              item.WaitingTime,
-             this._taskQueue.Limit,
-             count));
+             this._taskQueue));
 
-        private void NotifyItemEnqueued(int count, TaskItem item) => this._events?.ItemEnqueued?.Raise(new ItemEnqueuedEventArgs(
+        private void NotifyItemEnqueued(TaskItem item) => this._events?.ItemEnqueued?.Raise(new ItemEnqueuedEventArgs(
             item.Priority,
-            this._taskQueue.Limit,
-            count));
+            this._taskQueue));
 
         private void ProcessPendingTasks()
         {