perf(worker): pooled frame buffers — brings the net48 codec up to the gateway side's GWC-30 pattern

src/ZB.MOM.WW.MxGateway.Worker/Ipc/WorkerFrameReader.cs

@@ -9,11 +9,21 @@ using ZB.MOM.WW.MxGateway.Contracts.Proto;
 namespace ZB.MOM.WW.MxGateway.Worker.Ipc;
 
 /// <summary>Reads length-prefixed WorkerEnvelope protobuf frames from a stream.</summary>
+/// <remarks>
+///     <see cref="ReadAsync"/> is not reentrant: the reader keeps a per-instance length-prefix scratch
+///     buffer, so exactly one consumer may be inside a read at a time. That matches how the reader is
+///     used — a single read loop per <c>WorkerPipeSession</c>, with the startup handshake read
+///     completing before the loop starts.
+/// </remarks>
 public sealed class WorkerFrameReader
 {
     private readonly WorkerFrameProtocolOptions _options;
     private readonly Stream _stream;
 
+    // Reused across frames rather than allocated per read (GWC-30). Safe because ReadAsync is
+    // single-consumer by construction; the prefix is fully overwritten by every read.
+    private readonly byte[] _lengthPrefix = new byte[sizeof(uint)];
+
     /// <summary>Initializes the reader with a stream and protocol options.</summary>
     /// <param name="stream">Stream to read frames from.</param>
     /// <param name="options">Protocol options for frame validation.</param>
@@ -30,10 +40,9 @@ public sealed class WorkerFrameReader
     /// <returns>The validated <see cref="WorkerEnvelope"/> read from the stream.</returns>
     public async Task<WorkerEnvelope> ReadAsync(CancellationToken cancellationToken = default)
     {
-        byte[] lengthPrefix = new byte[sizeof(uint)];
-        await ReadExactlyOrThrowAsync(lengthPrefix, lengthPrefix.Length, cancellationToken).ConfigureAwait(false);
+        await ReadExactlyOrThrowAsync(_lengthPrefix, sizeof(uint), cancellationToken).ConfigureAwait(false);
 
-        uint payloadLength = ReadUInt32LittleEndian(lengthPrefix);
+        uint payloadLength = ReadUInt32LittleEndian(_lengthPrefix);
         if (payloadLength == 0)
         {
             throw new WorkerFrameProtocolException(

src/ZB.MOM.WW.MxGateway.Worker/Ipc/WorkerFrameWriter.cs

@@ -1,4 +1,5 @@
 using System;
+using System.Buffers;
 using System.Collections.Generic;
 using System.IO;
 using System.Runtime.ExceptionServices;
@@ -459,17 +460,27 @@ public sealed class WorkerFrameWriter
 
         _nextSequence = candidateSequence;
 
-        // Serialize once into a single buffer that carries the 4-byte length prefix followed by the
-        // payload, then issue one stream write. This avoids a second serialization pass, a separate
-        // prefix array, and a separate prefix write. The flush is deferred to the end of the drained
-        // batch (see DrainQueuedFramesAsync) so a burst of frames shares one flush.
+        // Serialize once into a single pooled buffer that carries the 4-byte length prefix followed
+        // by the payload, then issue one stream write. This avoids a second serialization pass, a
+        // separate prefix array, a separate prefix write, and any per-frame heap allocation — the
+        // gateway-side writer's GWC-30 shape, now matched on the net48 side. The rented buffer may
+        // be larger than requested, so only the first frameLength bytes are ever written. The buffer
+        // is returned only after this frame's write has completed; the batch flush deferred to the
+        // end of the drain (see DrainQueuedFramesAsync) does not read from it.
         int frameLength = sizeof(uint) + payloadLength;
-        byte[] frame = new byte[frameLength];
+        byte[] frame = ArrayPool<byte>.Shared.Rent(frameLength);
+        try
+        {
             WriteUInt32LittleEndian(frame, (uint)payloadLength);
             envelope.WriteTo(new Span<byte>(frame, sizeof(uint), payloadLength));
 
             await _stream.WriteAsync(frame, 0, frameLength, CancellationToken.None).ConfigureAwait(false);
         }
+        finally
+        {
+            ArrayPool<byte>.Shared.Return(frame);
+        }
+    }
 
     private static void WriteUInt32LittleEndian(
         byte[] buffer,