FFTCache pooling

Cavern/Utilities/FFTCache.cs

@@ -71,6 +71,7 @@ public FFTCache(int size) {
             }
 
             for (int i = 0, c = QMath.Log2(size); i < c; i++) {
+                Interlocked.Increment(ref refcounts[i]);
                 if (cos[i] != null) {
                     continue;
                 }
@@ -89,7 +90,6 @@ public FFTCache(int size) {
                         thisSin[j + 1] = sinValue;
                     }
                 }
-                Interlocked.Increment(ref refcounts[i]);
             }
 
             float[] maskSource = new float[Vector<float>.Count + 1];

Cavern/Utilities/FFTCachePool.cs

@@ -0,0 +1,56 @@
+using System;
+using System.Collections.Generic;
+
+namespace Cavern.Utilities {
+    /// <summary>
+    /// When performing a large amount of FFTs across multiple threads, use this pool for optimizing allocation performance
+    /// by reusing caches that are not used anymore by their thread.
+    /// </summary>
+    public class FFTCachePool : IDisposable {
+        /// <summary>
+        /// Caches not currently leased.
+        /// </summary>
+        readonly Stack<FFTCache> caches = new Stack<FFTCache>();
+
+        /// <summary>
+        /// Size of the used FFTs.
+        /// </summary>
+        readonly int size;
+
+        /// <summary>
+        /// Create an <see cref="FFTCache"/> pool for this FFT size.
+        /// </summary>
+        public FFTCachePool(int size) => this.size = size;
+
+        /// <summary>
+        /// Get an <see cref="FFTCache"/> to work with.
+        /// </summary>
+        public FFTCache Lease() {
+            lock (this) {
+                if (caches.Count == 0) {
+                    return new ThreadSafeFFTCache(size);
+                } else {
+                    return caches.Pop();
+                }
+            }
+        }
+
+        /// <summary>
+        /// Store the <paramref name="cache"/> for later reuse.
+        /// </summary>
+        public void Return(FFTCache cache) {
+            lock (this) {
+                caches.Push(cache);
+            }
+        }
+
+        /// <summary>
+        /// Free all resources used by the allocated <see cref="caches"/>.
+        /// </summary>
+        public void Dispose() {
+            while (caches.Count != 0) {
+                caches.Pop().Dispose();
+            }
+        }
+    }
+}