use max size semaphore

fix double release

stack-info: PR: #4220, branch: GarrettBeatty/gcbeatty/taskoptimization/3

Author: GarrettBeatty

sdk/src/Services/S3/Custom/Transfer/Internal/BufferedPartDataHandler.cs

@@ -153,9 +153,6 @@ private void ProcessStreamingPart(
                 // If ReleaseBufferSpace() throws, we no longer own the data source, so we won't dispose it
                 streamingDataSource = null;
 
-                // Release capacity immediately since we're not holding anything in memory
-                _partBufferManager.ReleaseBufferSpace();
-
                 _logger.DebugFormat("BufferedPartDataHandler: [Part {0}] StreamingDataSource added and capacity released",
                     partNumber);
             }

sdk/src/Services/S3/Custom/Transfer/Internal/MultipartDownloadManager.cs

@@ -159,7 +159,10 @@ public MultipartDownloadManager(IAmazonS3 s3Client, BaseDownloadRequest request,
             }
             else
             {
-                _httpConcurrencySlots = new SemaphoreSlim(_config.ConcurrentServiceRequests);
+                _httpConcurrencySlots = new SemaphoreSlim(
+                    _config.ConcurrentServiceRequests,  // initialCount
+                    _config.ConcurrentServiceRequests   // maxCount - prevents exceeding configured limit
+                );
                 _ownsHttpThrottler = true; // We own it, so we dispose it
             }
         }

sdk/src/Services/S3/Custom/Transfer/Internal/PartBufferManager.cs

@@ -199,7 +199,10 @@ public PartBufferManager(BufferedDownloadConfiguration config)
                 throw new ArgumentNullException(nameof(config));
 
             _partDataSources = new ConcurrentDictionary<int, IPartDataSource>();
-            _bufferSpaceAvailable = new SemaphoreSlim(config.MaxInMemoryParts);
+            _bufferSpaceAvailable = new SemaphoreSlim(
+                config.MaxInMemoryParts,  // initialCount
+                config.MaxInMemoryParts   // maxCount - prevents exceeding configured limit
+            );
             _partAvailable = new AutoResetEvent(false);
 
             Logger.DebugFormat("PartBufferManager initialized with MaxInMemoryParts={0}", config.MaxInMemoryParts);