complete infrastructure

Assets/UniRx.Async/Internal/PromisePool.cs

@@ -0,0 +1,53 @@
+using System.Collections.Concurrent;
+using System.Runtime.CompilerServices;
+using System.Threading;
+
+namespace UniRx.Async.Internal
+{
+    internal interface IPromisePoolItem
+    {
+        void Reset();
+    }
+
+    internal class PromisePool<T>
+        where T : class, IPromisePoolItem
+    {
+        int count = 0;
+        readonly ConcurrentQueue<T> queue = new ConcurrentQueue<T>();
+        readonly int maxSize;
+
+        public PromisePool(int maxSize = 256)
+        {
+            this.maxSize = maxSize;
+        }
+
+        [MethodImpl(MethodImplOptions.AggressiveInlining)]
+        public T TryRent()
+        {
+            if (queue.TryDequeue(out var value))
+            {
+                Interlocked.Decrement(ref count);
+                return value;
+            }
+
+            return null;
+        }
+
+        [MethodImpl(MethodImplOptions.AggressiveInlining)]
+        public bool TryReturn(T value)
+        {
+            value.Reset(); // reset when return.
+
+            if (count < maxSize)
+            {
+                queue.Enqueue(value);
+                Interlocked.Increment(ref count);
+                return true;
+            }
+            else
+            {
+                return false;
+            }
+        }
+    }
+}