FFI Segfaulting

magefile.go

// +build mage

package main

import (
	"fmt"
	"os"
	"os/exec"

	"github.com/magefile/mage/mg"
)

// Create the shared lib
func Build() error {
	fmt.Println("Compiling shared library...")
	cmd := exec.Command("go", "build", "-o", "object-loader.dylib", "-buildmode=c-shared", "main.go")
	return cmd.Run()
}

// Put the libs somewhere Ruby can find it
func Install() {
	mg.Deps(Build)
	fmt.Println("Installing...")
	os.Rename("./object-loader.dylib", "/usr/local/lib/object-loader.dylib")
	os.Rename("./object-loader.h", "/usr/local/lib/object-loader.h")
}

// Clean up after yourself
func Clean() {
	fmt.Println("Cleaning...")
	os.Remove("object-loader.dylib")
	os.Remove("object-loader.h")
}

// Make sure it runs from C
func TestC() {
	mg.Deps(Build)
	fmt.Println("Compiling C program")
	exec.Command("gcc", "-o", "test", "test.c", "./object-loader.dylib").Run()
	results, _ := exec.Command("./test").Output()
	fmt.Println("Testing it...")
	fmt.Print(string(results))
	os.Remove("./test")
}

main.go

package main

import (
	"database/sql"
	"fmt"
	"log"

	"C"

	_ "gopkg.in/goracle.v2"
)

var db *sql.DB

func init() {
	var err error
	connString := "" // connection string to database
	db, err = sql.Open("goracle", connString)
	if err != nil {
		log.Printf("Unable to connect to database: %v", err)
	}
}

//export LoadObject
func LoadObject(id int) *C.char {
	fmt.Println("Starting Query...")
	rows, err := db.Query("select * from users where id = :1", id)
	fmt.Println("Ran query")
	if err != nil {
		fmt.Printf("Unable to run query: %v\n", err)
		return C.CString("Failed to run query")
	}
	fmt.Println("Accessing rows")
	defer rows.Close()
	for rows.Next() {
		fmt.Println("Found a row")
	}
	fmt.Println("Returning")
	return C.CString("All done")
}

func main() {
}

test.c

#include <stdio.h>
#include "object-loader.h"

int main()
{
  GoInt userID = 4157737;
  char *result;
  result = LoadObject(userID);
  printf("%s", result);
  return 0;
}

use_it.rb

# frozen_string_literal: true

require 'ffi'

module ObjectLoader
  extend FFI::Library
  ffi_lib 'object-loader.dylib'
  attach_function :LoadObject, [:int], :string
end

threads = []
3.times do
  threads << Thread.new { puts ObjectLoader.LoadObject(31_859_085) }
end
threads.each(&:join)