Short practice for using Windows DLL in Go Language

a_windows_dll_test.go

package main

//
//	References
//	- https://medium.com/jettech/breaking-all-the-rules-using-go-to-call-windows-api-2cbfd8c79724
//

import (
	"math/rand"
	"os"
	"path/filepath"
	"plugin"
	"runtime"
	"syscall"
	"testing"
)

func testDllPath() string {
	name := "module1.dll"
	wd, _ := os.Getwd()
	mpath := filepath.Join(wd, "build", "Debug", name)
	return mpath
}

func TestTryLoadWithPath(t *testing.T) {
	mpath := testDllPath()
	if _, err := plugin.Open(mpath); err != nil {
		t.Log(err) // this can fail if not implemented
	}
}

func TestSyscallWindowsDLL(t *testing.T) {
	if runtime.GOOS != "windows" {
		t.SkipNow()
	}
	mpath := testDllPath()
	p, err := syscall.LoadDLL(mpath)
	if err != nil {
		t.Fatal(err)
	}
	defer p.Release()

	t.Log("handle", p.Handle)
	fn, err := p.FindProc("is_available")
	if err != nil {
		t.Fatal(err)
	}
	t.Logf("proc %s %x", fn.Name, fn.Addr())

	arg0 := uint32(16)
	ret1, _, err := fn.Call(uintptr(arg0))
	if err != syscall.Errno(0) {
		t.Log(err)
	}
	t.Log(ret1, ":=", fn.Name, "(", arg0, ")")
}

func TestSyscallParallel(t *testing.T) {
	if runtime.GOOS != "windows" {
		t.SkipNow()
	}

	mpath := testDllPath()
	p, err := syscall.LoadDLL(mpath)
	if err != nil {
		t.Fatal(err)
	}
	defer p.Release()
	fn, err := p.FindProc("is_available")
	if err != nil {
		t.Fatal(err)
	}

	requests := make(chan uint32, 10)
	defer close(requests)

	serve := func(arg0 uint32) (uintptr, error) {
		ret1, _, err := fn.Call(uintptr(arg0))
		if err != syscall.Errno(0) {
			return ret1, err
		}
		return ret1, nil
	}
	worker := func(id uint32, reqs <-chan uint32) {
		for req := range reqs {
			ret, err := serve(req)
			if err != nil {
				t.Log(id, "failed", err)
			} else {
				t.Log(id, ret, "<--", req)
			}
		}
	}

	go worker(0xA, requests)
	go worker(0xB, requests)
	go worker(0xC, requests)
	go worker(0xD, requests)

	for i := 0; i < 50; i++ {
		requests <- rand.Uint32()
	}
}

cpp_build.cmake

cmake_minimum_required(VERSION 3.14)

project(module1 LANGUAGES CXX)

add_library(module1 SHARED
    cpp_export.h
    cpp_libmain.cpp
    cpp_export_c.cpp
)
set_target_properties(module1
PROPERTIES
    CXX_STANDARD 20
)

cpp_export.h

#pragma once
// clang-format off
#   if defined(_MSC_VER) // MSVC
#       define _HIDDEN_
#       ifdef _WINDLL
#           define _INTERFACE_ __declspec(dllexport)
#       else
#           define _INTERFACE_ __declspec(dllimport)
#       endif
#   elif defined(__GNUC__) || defined(__clang__)
#       define _INTERFACE_ __attribute__((visibility("default")))
#       define _HIDDEN_ __attribute__((visibility("hidden")))
#   else
#       error "unexpected compiler"
#   endif // compiler check
// clang-format on

#include <cstdint>

namespace space1
{
_INTERFACE_ bool is_available(uint32_t idx) noexcept;
}

cpp_export_c.cpp

#include "cpp_export.h"

extern "C"
{
    _INTERFACE_ uint32_t is_available(uint32_t idx) noexcept
    {
        return space1::is_available(idx);
    }
}

cpp_libmain.cpp

#include "cpp_export.h"

namespace space1
{
bool is_available(uint32_t idx) noexcept
{
    return idx < 4;
}
} // namespace space1

Exported symbols in DLL with https://github.com/lucasg/Dependencies