Unload MsQuic after checking for QUIC support to free resources. (#74749)

* Unload MsQuic after checking for QUIC support to free resources.

* Unload MsQuic unconditionally

* Code review feedback

Author: rzikm

src/libraries/System.Net.Quic/src/System/Net/Quic/Internal/MsQuicApi.cs

@@ -1,6 +1,7 @@
 // Licensed to the .NET Foundation under one or more agreements.
 // The .NET Foundation licenses this file to you under the MIT license.
 
+using System.Diagnostics;
 using System.Diagnostics.CodeAnalysis;
 using System.Runtime.InteropServices;
 using Microsoft.Quic;
@@ -47,7 +48,8 @@ private MsQuicApi(QUIC_API_TABLE* apiTable)
         }
     }
 
-    internal static MsQuicApi Api { get; } = null!;
+    private static readonly Lazy<MsQuicApi> _api = new Lazy<MsQuicApi>(AllocateMsQuicApi);
+    internal static MsQuicApi Api => _api.Value;
 
     internal static bool IsQuicSupported { get; }
 
@@ -58,29 +60,21 @@ private MsQuicApi(QUIC_API_TABLE* apiTable)
 
     static MsQuicApi()
     {
-        IntPtr msQuicHandle;
-        if (!NativeLibrary.TryLoad($"{Interop.Libraries.MsQuic}.{MsQuicVersion.Major}", typeof(MsQuicApi).Assembly, DllImportSearchPath.AssemblyDirectory, out msQuicHandle) &&
-            !NativeLibrary.TryLoad(Interop.Libraries.MsQuic, typeof(MsQuicApi).Assembly, DllImportSearchPath.AssemblyDirectory, out msQuicHandle))
+        if (!TryLoadMsQuic(out IntPtr msQuicHandle))
         {
             return;
         }
 
         try
         {
-            if (!NativeLibrary.TryGetExport(msQuicHandle, "MsQuicOpenVersion", out IntPtr msQuicOpenVersionAddress))
-            {
-                return;
-            }
-
-            QUIC_API_TABLE* apiTable = null;
-            delegate* unmanaged[Cdecl]<uint, QUIC_API_TABLE**, int> msQuicOpenVersion = (delegate* unmanaged[Cdecl]<uint, QUIC_API_TABLE**, int>)msQuicOpenVersionAddress;
-            if (StatusFailed(msQuicOpenVersion((uint)MsQuicVersion.Major, &apiTable)))
+            if (!TryOpenMsQuic(msQuicHandle, out QUIC_API_TABLE* apiTable))
             {
                 return;
             }
 
             try
             {
+                // Check version
                 int arraySize = 4;
                 uint* libVersion = stackalloc uint[arraySize];
                 uint size = (uint)arraySize * sizeof(uint);
@@ -99,7 +93,7 @@ static MsQuicApi()
                     return;
                 }
 
-                // Assume SChannel is being used on windows and query for the actual provider from the library
+                // Assume SChannel is being used on windows and query for the actual provider from the library if querying is supported
                 QUIC_TLS_PROVIDER provider = OperatingSystem.IsWindows() ? QUIC_TLS_PROVIDER.SCHANNEL : QUIC_TLS_PROVIDER.OPENSSL;
                 size = sizeof(QUIC_TLS_PROVIDER);
                 apiTable->GetParam(null, QUIC_PARAM_GLOBAL_TLS_PROVIDER, &size, &provider);
@@ -122,26 +116,67 @@ static MsQuicApi()
                     Tls13ClientMayBeDisabled = IsTls13Disabled(isServer: false);
                 }
 
-                Api = new MsQuicApi(apiTable);
                 IsQuicSupported = true;
             }
             finally
             {
-                if (!IsQuicSupported && NativeLibrary.TryGetExport(msQuicHandle, "MsQuicClose", out IntPtr msQuicClose))
-                {
-                    // Gracefully close the API table
-                    ((delegate* unmanaged[Cdecl]<QUIC_API_TABLE*, void>)msQuicClose)(apiTable);
-                }
+                // Gracefully close the API table to free resources. The API table will be allocated lazily again if needed
+                bool closed = TryCloseMsQuic(msQuicHandle, apiTable);
+                Debug.Assert(closed, "Failed to close MsQuic");
             }
-
         }
         finally
         {
-            if (!IsQuicSupported)
-            {
-                NativeLibrary.Free(msQuicHandle);
-            }
+            // Unload the library, we will load it again when we actually use QUIC
+            NativeLibrary.Free(msQuicHandle);
+        }
+    }
+
+    private static MsQuicApi AllocateMsQuicApi()
+    {
+        Debug.Assert(IsQuicSupported);
+
+        if (TryLoadMsQuic(out IntPtr msQuicHandle) &&
+            TryOpenMsQuic(msQuicHandle, out QUIC_API_TABLE* apiTable))
+        {
+            return new MsQuicApi(apiTable);
+        }
+
+        throw new Exception("Failed to create MsQuicApi instance");
+    }
+
+    private static bool TryLoadMsQuic(out IntPtr msQuicHandle) =>
+        NativeLibrary.TryLoad($"{Interop.Libraries.MsQuic}.{MsQuicVersion.Major}", typeof(MsQuicApi).Assembly, DllImportSearchPath.AssemblyDirectory, out msQuicHandle) ||
+        NativeLibrary.TryLoad(Interop.Libraries.MsQuic, typeof(MsQuicApi).Assembly, DllImportSearchPath.AssemblyDirectory, out msQuicHandle);
+
+    private static bool TryOpenMsQuic(IntPtr msQuicHandle, out QUIC_API_TABLE* apiTable)
+    {
+        apiTable = null;
+        if (!NativeLibrary.TryGetExport(msQuicHandle, "MsQuicOpenVersion", out IntPtr msQuicOpenVersionAddress))
+        {
+            return false;
+        }
+
+        QUIC_API_TABLE* table = null;
+        delegate* unmanaged[Cdecl]<uint, QUIC_API_TABLE**, int> msQuicOpenVersion = (delegate* unmanaged[Cdecl]<uint, QUIC_API_TABLE**, int>)msQuicOpenVersionAddress;
+        if (StatusFailed(msQuicOpenVersion((uint)MsQuicVersion.Major, &table)))
+        {
+            return false;
         }
+
+        apiTable = table;
+        return true;
+    }
+
+    private static bool TryCloseMsQuic(IntPtr msQuicHandle, QUIC_API_TABLE* apiTable)
+    {
+        if (NativeLibrary.TryGetExport(msQuicHandle, "MsQuicClose", out IntPtr msQuicClose))
+        {
+            ((delegate* unmanaged[Cdecl]<QUIC_API_TABLE*, void>)msQuicClose)(apiTable);
+            return true;
+        }
+
+        return false;
     }
 
     private static bool IsWindowsVersionSupported() => OperatingSystem.IsWindowsVersionAtLeast(MinWindowsVersion.Major,