Add GPU lease warm-up and shared limiter

PerfectNumbers.Core/Gpu/GpuContextPool.cs

@@ -50,13 +50,23 @@ public static class GpuContextPool
 	// Allows callers to choose CPU/GPU per use-case, decoupled from ForceCpu.
 	public static GpuContextLease Rent()
 	{
-		if (GpuPool.TryDequeue(out var gpu))
-		{
-			return new GpuContextLease(gpu);
-		}
+		GpuPrimeLeaseLimiter.Enter();
 
-		// Create a new accelerator when the pool does not have one available.
-		return new GpuContextLease(new PooledContext());
+		try
+		{
+			if (GpuPool.TryDequeue(out var gpu))
+			{
+				return new GpuContextLease(gpu);
+			}
+
+			// Create a new accelerator when the pool does not have one available.
+			return new GpuContextLease(new PooledContext());
+		}
+		catch
+		{
+			GpuPrimeLeaseLimiter.Exit();
+			throw;
+		}
 	}
 
 	public static void WarmUpPool(int threadCount)
@@ -96,23 +106,33 @@ public static class GpuContextPool
 	{
 		ctx.Accelerator.Synchronize();
 		GpuPool.Enqueue(ctx);
+		GpuPrimeLeaseLimiter.Exit();
 	}
 
-	public readonly struct GpuContextLease
+	public struct GpuContextLease
 	{
-		private readonly PooledContext _ctx;
+		private PooledContext? _ctx;
+		private bool _disposed;
 
 		internal GpuContextLease(PooledContext ctx)
 		{
 			_ctx = ctx;
+			_disposed = false;
 		}
 
-		public readonly Context Context => _ctx.Context;
-		public readonly Accelerator Accelerator => _ctx.Accelerator;
+		public Context Context => _ctx!.Context;
+		public Accelerator Accelerator => _ctx!.Accelerator;
 
-		public readonly void Dispose()
+		public void Dispose()
 		{
-			Return(_ctx);
+			if (_disposed)
+			{
+				return;
+			}
+
+			_disposed = true;
+			Return(_ctx!);
+			_ctx = null;
 		}
 	}
 }

PerfectNumbers.Core/Gpu/GpuPrimeLeaseLimiter.cs

@@ -0,0 +1,37 @@
+using System.Threading;
+
+namespace PerfectNumbers.Core.Gpu;
+
+public static class GpuPrimeLeaseLimiter
+{
+        private static SemaphoreSlim _semaphore = new(int.MaxValue, int.MaxValue);
+        private static int _currentLimit = int.MaxValue;
+
+        public static void Initialize(int limit)
+        {
+                if (limit <= 0)
+                {
+                        limit = 1;
+                }
+
+                if (limit == _currentLimit)
+                {
+                        return;
+                }
+
+                var previous = _semaphore;
+                _semaphore = new SemaphoreSlim(limit, limit);
+                _currentLimit = limit;
+                previous.Dispose();
+        }
+
+        public static void Enter()
+        {
+                _semaphore.Wait();
+        }
+
+        public static void Exit()
+        {
+                _semaphore.Release();
+        }
+}

PerfectNumbers.Core/PrimeTester.cs

@@ -159,18 +159,7 @@ public sealed class PrimeTester
 				return;
 			}
 
-			int toWarm = target - WarmedGpuLeaseCount;
-			var leases = new PrimeTesterGpuContextPool.PrimeTesterGpuContextLease[toWarm];
-			for (int i = 0; i < toWarm; i++)
-			{
-				leases[i] = PrimeTesterGpuContextPool.Rent(GpuBatchSize);
-			}
-
-			for (int i = 0; i < toWarm; i++)
-			{
-				leases[i].Dispose();
-			}
-
+			PrimeTesterGpuContextPool.WarmUp(target, GpuBatchSize);
 			WarmedGpuLeaseCount = target;
 		}
 	}
@@ -229,6 +218,8 @@ public sealed class PrimeTester
 	internal static class PrimeTesterGpuContextPool
 	{
 		private static readonly ConcurrentQueue<PrimeTesterGpuContextLease> Pool = new();
+		private static readonly object WarmUpLock = new();
+		private static int WarmedLeaseCount;
 		private static readonly object SharedTablesLock = new();
 		private static readonly Dictionary<string, SharedHeuristicGpuTables> SharedTables = new();
 
@@ -267,25 +258,60 @@ public sealed class PrimeTester
 			}
 		}
 
-		internal static PrimeTesterGpuContextLease Rent(int minBufferCapacity = 1)
+		internal static void WarmUp(int target, int minBufferCapacity)
 		{
-			if (!Pool.TryDequeue(out var lease))
+			if (target <= 0)
 			{
-				lease = new PrimeTesterGpuContextLease(minBufferCapacity);
-			}
-			else
-			{
-				lease.EnsureCapacity(minBufferCapacity);
+				return;
 			}
 
-			lease.ResetReturnFlag();
-			return lease;
+			lock (WarmUpLock)
+			{
+				if (target <= WarmedLeaseCount)
+				{
+					return;
+				}
+
+				int toCreate = target - WarmedLeaseCount;
+				for (int i = 0; i < toCreate; i++)
+				{
+					Pool.Enqueue(new PrimeTesterGpuContextLease(minBufferCapacity));
+				}
+
+				WarmedLeaseCount = target;
+			}
+		}
+
+		internal static PrimeTesterGpuContextLease Rent(int minBufferCapacity = 1)
+		{
+			GpuPrimeLeaseLimiter.Enter();
+
+			try
+			{
+				if (!Pool.TryDequeue(out var lease))
+				{
+					lease = new PrimeTesterGpuContextLease(minBufferCapacity);
+				}
+				else
+				{
+					lease.EnsureCapacity(minBufferCapacity);
+				}
+
+				lease.ResetReturnFlag();
+				return lease;
+			}
+			catch
+			{
+				GpuPrimeLeaseLimiter.Exit();
+				throw;
+			}
 		}
 
 		internal static void Return(PrimeTesterGpuContextLease lease)
 		{
 			lease.Accelerator.Synchronize();
 			Pool.Enqueue(lease);
+			GpuPrimeLeaseLimiter.Exit();
 		}
 
 		internal static void DisposeAll()
@@ -304,6 +330,8 @@ public sealed class PrimeTester
 
 				SharedTables.Clear();
 			}
+
+			WarmedLeaseCount = 0;
 		}
 
 		internal static void Clear(Accelerator accelerator)
@@ -313,23 +341,28 @@ public sealed class PrimeTester
 				return;
 			}
 
-			var retained = new List<PrimeTesterGpuContextLease>();
-			while (Pool.TryDequeue(out var lease))
+			lock (WarmUpLock)
 			{
-				if (lease.Accelerator == accelerator)
+				var retained = new List<PrimeTesterGpuContextLease>();
+				while (Pool.TryDequeue(out var lease))
 				{
-					lease.DisposeResources();
+					if (lease.Accelerator == accelerator)
+					{
+						lease.DisposeResources();
+					}
+					else
+					{
+						retained.Add(lease);
+					}
 				}
-				else
-				{
-					retained.Add(lease);
-				}
-			}
 
-			int retainedCount = retained.Count;
-			for (int i = 0; i < retainedCount; i++)
-			{
-				Pool.Enqueue(retained[i]);
+				int retainedCount = retained.Count;
+				for (int i = 0; i < retainedCount; i++)
+				{
+					Pool.Enqueue(retained[i]);
+				}
+
+				WarmedLeaseCount = Pool.Count;
 			}
 		}