Once this is approved, I'll also create a backport PR.

Adhoc distribtests: https://g3c.corp.google.com/results/invocations/a25cde5a-bf1c-49cc-923e-315e96987e17 (including the newly added single file publish distribtest).

Another adhoc distribtest run: https://g3c.corp.google.com/results/invocations/8872dc43-c7da-4533-b792-bc1c5eaff03b/targets

Yet another adhoc distribtest: https://g3c.corp.google.com/results/invocations/700ebfdb-8e9a-43c8-9e43-2e58a4929037

https://github.com/grpc/grpc/blob/master/src/csharp/Grpc.Core/Internal/UnmanagedLibrary.cs#L245 is another problem that needs to be fixed to make the single file scenario working. There is no libcoreclr.so on disk in the single file scenario.

https://github.com/grpc/grpc/blob/master/src/csharp/Grpc.Core/Internal/UnmanagedLibrary.cs#L245 is another problem that needs to be fixed to make the single file scenario working. There is no libcoreclr.so on disk in the single file scenario.

Ok, thanks for the tip. Do you have ideas on how to fix this problem?

@jtattermusch please add a distribtest for the IncludeNativeLibrariesForSelfExtract case. Hopefully @jkotas can advise on how to detect and/or handle that too?

Do you have ideas on how to fix this problem?

The best way to fix this problem is to use Native.Load for .NET Core. This API deals with all probing paths, single file and platform differences, including IncludeNativeLibrariesForSelfExtract.

Native.Load

Thanks for the tip! Unfortunately Native.Load is only available on .NET Core 3+ (and at this point the newest we target is netstandard2.0)

Another distribtest: https://g3c.corp.google.com/results/invocations/757851c5-c719-4434-bad6-bac0e655990b/targets

The interop test failure is #24764.

As @jkotas has pointed out, I'm now getting the Unhandled exception. System.DllNotFoundException: Unable to load shared library 'libcoreclr.so' error.

https://source.cloud.google.com/results/invocations/9ccd7ae8-32c0-4ee9-b08a-e7848b2f84a4/targets/github%2Fgrpc/tests

@yulin-liang I don't have a fully working fix at this point, so I think it's fine to cut the release branch without it. (If I come up with a fix, I can backport it)

Unfortunately Native.Load is only available on .NET Core 3+ (and at this point the newest we target is netstandard2.0)

The fix for this should be to try to lookup these methods using reflection, and then use them instead of the hardcoded P/Invokes when these methods are available. Something like:

delegate bool TryLoadDelegate(string libraryName, System.Reflection.Assembly assembly, System.Runtime.InteropServices.DllImportSearchPath? searchPath, out IntPtr handle);
delegate bool TryGetExportDelegate(IntPtr handle, string name, out IntPtr address);

static TryLoadDelegate s_tryLoad;
static TryGetExportDelegate s_tryGetExport; 

...

Type nativeLibrary = Type.GetType("System.Runtime.InteropServices.NativeLibrary, System.Runtime.InteropServices, PublicKeyToken=b03f5f7f11d50a3a", throwOnError: false);
if (nativeLibrary == null)
    return;

MethodInfo tryLoad = nativeLibrary.GetMethod("TryLoad", BindingFlags.Static | BindingFlags.Public, null,
    new Type[] { typeof(string), typeof(Assembly), typeof(Nullable<DllImportSearchPath>), typeof(IntPtr).MakeByRefType() }, null);
s_tryLoad = (TryLoadDelegate)tryLoad?.CreateDelegate(typeof(TryLoadDelegate));

MethodInfo tryGetExport = nativeLibrary.GetMethod("TryLoad", BindingFlags.Static | BindingFlags.Public, null,
    new Type[] { typeof(IntPtr), typeof(string), typeof(IntPtr).MakeByRefType() }, null);
s_tryGetExport = (TryGetExportDelegate)tryGetExport?.CreateDelegate(typeof(TryGetExportDelegate));

Alternative approach used by a library that faced a similar problem: gui-cs/Terminal.Gui@19955fa#diff-91d94d0e5b8dd01a182c51299d7e8093247fa636a9768574b7042bfd5df9a1deR261

I refactored the native library loading logic to use the default DllImport loading mechanism when on .NET Core.
It leads to some code simplification and also seems to handle the case with of .NET 5 single file published app well.
PTAL.

The adhoc distribtest run is here: https://g3c.corp.google.com/results/invocations/4da3122d-8972-48ff-ac92-d01b22705b99/log

Known failures: build_docker_go is also failing on master.

Adhoc distribtests are passing:
https://g3c.corp.google.com/results/invocations/50ae873b-5510-4ae0-b735-0840c7e9dd6d/targets/grpc%2Fcore%2Fexperimental%2Fgrpc_distribtests_multiplatform/log (the php7 distribtest has actually failed but that's unrelated to this PR - everything C# related is green)

dotnet 5 distribtest is also green:
https://g3c.corp.google.com/results/invocations/4228feb1-e59b-4bb1-9933-982998e8d431/targets/github%2Fgrpc;config=default/tests;query=csharp

@jkotas your opinions on the approach I ended up taking (= rely on DllImport default loading logic) are welcome.

@apolcyn PTAL.

@jkotas your opinions on the approach I ended up taking

Looks fine to me.

@jtattermusch does your fix handle the IncludeNativeLibrariesForSelfExtract case too?

@jtattermusch does your fix handle the IncludeNativeLibrariesForSelfExtract case too?

I haven't tested that explicitly - would you mind trying it out and posting back the result?

The nightly build of the nugets should appear here soon:
https://packages.grpc.io/

Alternatively, here are nugets from my last manual build:
https://storage.cloud.google.com/grpc-testing-kokoro-prod/test_result_public/prod/grpc/core/master/linux/grpc_build_packages/14907/20201130-052042/github/grpc/artifacts/csharp_nugets_windows_dotnetcli.zip

I wanted to merge this PR ASAP because like this the fixes will still make it to Grpc.Core 2.34.0 release - we can address IncludeNativeLibrariesForSelfExtract as a follow up.

@jtattermusch I did a test with Grpc.Core version 2.34.0 and it works for IncludeNativeLibrariesForSelfExtract too! 😀