Allow memory-mapped file to open for shared reading

microsoft · Apr 25, 2022 · 02c4fec · 02c4fec
1 parent 054aabf
commit 02c4fec
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Showing 2 changed files with 11 additions and 2 deletions.
diff --git a/src/Microsoft.Windows.CsWin32/MetadataIndex.cs b/src/Microsoft.Windows.CsWin32/MetadataIndex.cs
@@ -250,11 +250,12 @@ internal static MetadataIndex Get(string metadataPath, Platform? platform)
                 // Read the entire metadata file exactly once so that many MemoryStreams can share the memory.
                 if (!MetadataFiles.TryGetValue(metadataPath, out MemoryMappedFile? file))
                 {
-                    file = MemoryMappedFile.CreateFromFile(metadataPath);
+                    FileStream metadataStream = new FileStream(metadataPath, FileMode.Open, FileAccess.Read, FileShare.Read);
+                    file = MemoryMappedFile.CreateFromFile(metadataStream, mapName: null, capacity: 0, MemoryMappedFileAccess.Read, HandleInheritability.None, leaveOpen: false);
                     MetadataFiles.Add(metadataPath, file);
                 }
 
-                metadataBytes = file.CreateViewStream();
+                metadataBytes = file.CreateViewStream(offset: 0, size: 0, MemoryMappedFileAccess.Read);
             }
 
             return new MetadataIndex(metadataPath, metadataBytes, platform);

diff --git a/test/Microsoft.Windows.CsWin32.Tests/GeneratorTests.cs b/test/Microsoft.Windows.CsWin32.Tests/GeneratorTests.cs
@@ -2429,6 +2429,14 @@ public void CocreatableStructs()
         Assert.Contains(classDecl.AttributeLists, al => al.Attributes.Any(a => a.Name.ToString().Contains("ComImport")));
     }
 
+    [Fact]
+    public void OpensMetadataForSharedReading()
+    {
+        using FileStream competingReader = File.OpenRead(MetadataPath);
+        this.generator = this.CreateGenerator();
+        Assert.True(this.generator.TryGenerate("CreateFile", CancellationToken.None));
+    }
+
     private static string ConstructGlobalConfigString(bool omitDocs = false)
     {
         StringBuilder globalConfigBuilder = new();