Merge pull request #1928 from tyrielv/tyrielv/oom-connection-pool-size

Increase HTTP connection pool default to 2xCPU count and allow configuration override

Author: tyrielv

GVFS/GVFS.Common/GVFSConstants.cs

@@ -46,6 +46,8 @@ public static class GitConfig
 
             public const string ShowHydrationStatus = GVFSPrefix + "show-hydration-status";
             public const bool ShowHydrationStatusDefault = false;
+
+            public const string MaxHttpConnectionsConfig = GVFSPrefix + "max-http-connections";
         }
 
         public static class LocalGVFSConfig

GVFS/GVFS.Common/Http/HttpRequestor.cs

@@ -22,6 +22,7 @@ public abstract class HttpRequestor : IDisposable
 
         private static long requestCount = 0;
         private static SemaphoreSlim availableConnections;
+        private static int connectionLimitConfigured = 0;
 
         private readonly ProductInfoHeaderValue userAgentHeader;
 
@@ -37,8 +38,12 @@ static HttpRequestor()
             using (var machineConfigLock = GetMachineConfigLock())
             {
                 ServicePointManager.SecurityProtocol = ServicePointManager.SecurityProtocol | SecurityProtocolType.Tls12;
-                ServicePointManager.DefaultConnectionLimit = Environment.ProcessorCount;
-                availableConnections = new SemaphoreSlim(ServicePointManager.DefaultConnectionLimit);
+
+                // HTTP downloads are I/O-bound, not CPU-bound, so we default to
+                // 2x ProcessorCount. Can be overridden via gvfs.max-http-connections.
+                int connectionLimit = 2 * Environment.ProcessorCount;
+                ServicePointManager.DefaultConnectionLimit = connectionLimit;
+                availableConnections = new SemaphoreSlim(connectionLimit);
             }
         }
 
@@ -50,6 +55,13 @@ protected HttpRequestor(ITracer tracer, RetryConfig retryConfig, Enlistment enli
 
             this.Tracer = tracer;
 
+            // On first instantiation, check git config for a custom connection limit.
+            // This runs before any requests are made (during mount initialization).
+            if (Interlocked.CompareExchange(ref connectionLimitConfigured, 1, 0) == 0)
+            {
+                TryApplyConnectionLimitFromConfig(tracer, enlistment);
+            }
+
             HttpClientHandler httpClientHandler = new HttpClientHandler() { UseDefaultCredentials = true };
 
             this.authentication.ConfigureHttpClientHandlerSslIfNeeded(this.Tracer, httpClientHandler, enlistment.CreateGitProcess());
@@ -362,6 +374,58 @@ private static bool TryGetResponseMessageFromHttpRequestException(HttpRequestExc
 
         }
 
+        private static void TryApplyConnectionLimitFromConfig(ITracer tracer, Enlistment enlistment)
+        {
+            try
+            {
+                GitProcess.ConfigResult result = enlistment.CreateGitProcess().GetFromConfig(GVFSConstants.GitConfig.MaxHttpConnectionsConfig);
+                string error;
+                int configuredLimit;
+                if (!result.TryParseAsInt(0, 1, out configuredLimit, out error))
+                {
+                    EventMetadata metadata = new EventMetadata();
+                    metadata.Add("error", error);
+                    tracer.RelatedWarning(metadata, "HttpRequestor: Invalid gvfs.max-http-connections config value, using default");
+                    return;
+                }
+
+                if (configuredLimit > 0)
+                {
+                    int currentLimit = ServicePointManager.DefaultConnectionLimit;
+                    ServicePointManager.DefaultConnectionLimit = configuredLimit;
+
+                    // Adjust the existing semaphore rather than replacing it, so any
+                    // in-flight waiters release permits to the correct instance.
+                    int delta = configuredLimit - currentLimit;
+                    if (delta > 0)
+                    {
+                        for (int i = 0; i < delta; i++)
+                        {
+                            availableConnections.Release();
+                        }
+                    }
+                    else if (delta < 0)
+                    {
+                        for (int i = 0; i < -delta; i++)
+                        {
+                            availableConnections.Wait();
+                        }
+                    }
+
+                    EventMetadata metadata = new EventMetadata();
+                    metadata.Add("configuredLimit", configuredLimit);
+                    metadata.Add("previousLimit", currentLimit);
+                    tracer.RelatedEvent(EventLevel.Informational, "HttpRequestor_ConnectionLimitConfigured", metadata);
+                }
+            }
+            catch (Exception e)
+            {
+                EventMetadata metadata = new EventMetadata();
+                metadata.Add("Exception", e.ToString());
+                tracer.RelatedWarning(metadata, "HttpRequestor: Failed to read gvfs.max-http-connections config, using default");
+            }
+        }
+
         private static FileStream GetMachineConfigLock()
         {
             var machineConfigLocation = RuntimeEnvironment.SystemConfigurationFile;