Warning

This feature is officially unsupported by .NET! Doing so; you accept full responsibility for all side-effects that may happen.

That being said, lets get into it! Here are some resources that may come in handy!

• DllMain entry point
• Best Practices
• Vanara.PInvoke.Kernel32 is a great package for any Win32 API related stuff!
  • I recommend adding a global using static Vanara.PInvoke.Kernel32; to your projects to have things feel just like C++

Warning

DllMain should still be re-linked by some non-C# language. Exporting a C# DllMain will deadlock your program in .NET 10. More info here

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Basically the package is adding these targets to your .csproj

<Target Name="RemoveDLLMainObjects" AfterTargets="SetupOSSpecificProps">
    <PropertyGroup>
        <MicrosoftDllMain>$(IlcSdkPath)dllmain$(ObjectSuffix)</MicrosoftDllMain>
        <MicrosoftDllMainGuardCF>$(IlcSdkPath)dllmain.GuardCF$(ObjectSuffix)</MicrosoftDllMainGuardCF>
        <EnableControlFlowGuard>false</EnableControlFlowGuard>
    </PropertyGroup>

    <ItemGroup Condition="'$(_targetOS)' == 'win'">
        <LinkerArg Remove="&quot;$(MicrosoftDllMain)&quot;"/>
        <LinkerArg Remove="&quot;$(MicrosoftDllMainGuardCF)&quot;"/>
        <NativeLibrary Remove="$(MicrosoftDllMain)"/>
        <NativeLibrary Remove="$(MicrosoftDllMainGuardCF)"/>
    </ItemGroup>
</Target>

Why does my C# DllMain deadlock in .NET 10+?

The main thread is waiting for the finalizer thread to start. The runtime is initializing the GC, then waiting for the finalizer thread to start, which was not the case in .NET 6-9

The .NET Finalizer thread will start when the loader lock is lifted. While we're in the loader lock, we're waiting for the .NET Finalizer thread to start.

Native Stack Trace of .NET 10 deadlock under loader lock

Thread ID	Address	To	From	Size	Party	Comment
31208 - Main Thread
	00000000000CF088	00007FFD52E1DF83	00007FFD55A22714	2F0	System	ntdll.ZwWaitForMultipleObjects+14
	00000000000CF378	00007FFBDFDCC4EA	00007FFD52E1DF83	40	User	kernelbase.WaitForMultipleObjectsEx+123
	00000000000CF3B8	00007FFBDFDD3CA6	00007FFBDFDCC4EA	40	User	<native_aot_library>.PalCompatibleWaitAny+3A
	00000000000CF3F8	00007FFBDFDC477B	00007FFBDFDD3CA6	30	User	<native_aot_library>.CLREventStatic::Wait+C6
	00000000000CF428	00007FFBDFDC021B	00007FFBDFDC477B	30	User	<native_aot_library>.RhWaitForFinalizerThreadStart+1B
	00000000000CF458	00007FFBDFDC715B	00007FFBDFDC021B	40	User	<native_aot_library>.InitializeGC+DB
	00000000000CF498	00007FFBDFDBF911	00007FFBDFDC715B	50	User	<native_aot_library>.RhInitialize+16B
	00000000000CF4E8	00007FFBDFDC2539	00007FFBDFDBF911	30	User	<native_aot_library>.InitializeRuntime+11
	00000000000CF518	00007FFBDFBF30D9	00007FFBDFDC2539	50	User	<native_aot_library>.RhpReversePInvokeAttachOrTrapThread2+69
	00000000000CF568	00007FFBDFE2640A	00007FFBDFBF30D9	60	User	<native_aot_library>.Managed__DllMain+29
	00000000000CF5C8	00007FFD55A1F86E	00007FFBDFE2640A	30	System	<native_aot_library>.dllmain_dispatch+8A
	00000000000CF5F8	00007FFD558CBCAE	00007FFD55A1F86E	70	System	ntdll.LdrpCallInitRoutineInternal+22
	00000000000CF668	00007FFD558C97AC	00007FFD558CBCAE	110	System	ntdll.LdrpCallInitRoutine+10E
	00000000000CF778	00007FFD559576EA	00007FFD558C97AC	40	System	ntdll.LdrpInitializeNode+19C
	00000000000CF7B8	00007FFD55956203	00007FFD559576EA	40	System	ntdll.LdrpInitializeGraphRecurse+6A
	00000000000CF7F8	00007FFD558D6414	00007FFD55956203	90	System	ntdll.LdrpPrepareModuleForExecution+EF
	00000000000CF888	00007FFD558D6020	00007FFD558D6414	1D0	System	ntdll.LdrpLoadDllInternal+284
	00000000000CFA58	00007FFD558FFA20	00007FFD558D6020	F0	System	ntdll.LdrpLoadDll+100
	00000000000CFB48	00007FFD52E1CA5F	00007FFD558FFA20	70	System	ntdll.LdrLoadDll+170
	00000000000CFBB8	00007FF6E18B76E9	00007FFD52E1CA5F	8	User	kernelbase.LoadLibraryExW+FF
	00000000000CFBC0	0000000000000000	00007FF6E18B76E9		User	00007FF6E18B76E9