GO: AtExit function without modification in main

example.go

// A litte example
package main

import (
	"fmt"
	"progtrailer"
)

func main() {
	defer func() {
		fmt.Println("Defered fonction in main")
	}()

	fmt.Println("Start of program")
	
	progtrailer.AtExit(func() {
		fmt.Println("Executed at exit by AtExit")
	})
	
	fmt.Println("End of program")
	
	// Friendly Exit
	progtrailer.Exit(0)
	
	// After this, Code not executed
	fmt.Println("Not Executed")
}

prog_trailer.go

/* This package has an AtExit function without modification in neither in `main` package, neither in `main` function
Too, it has an Exit funtion which allow defer functions in the `main` function:
```
func main() {
	defer func() {
		// It will be executed
	}()
	progtrailer.Exit(0)
}
```
*/
package progtrailer

import (
	"os"
	"runtime"
	"sync"
	"sync/atomic"
	"time"
)

// Synchronized list for avoiding races
type tSyncHandlerList struct {
	list []func()
	m    sync.Mutex
}

func (l *tSyncHandlerList) Add(h func()) {
	l.m.Lock()
	defer l.m.Unlock()

	l.list = append(l.list, h)
}

func (l *tSyncHandlerList) Get() []func() {
	l.m.Lock()
	defer l.m.Unlock()

	res := make([]func(), len(l.list))
	copy(res, l.list)

	return res
}

var exitCode int64
var handlers tSyncHandlerList

func init() {
	go func() {
		t := time.NewTicker(500 * time.Millisecond)
		for _ = range t.C {
			if runtime.NumGoroutine() < 2 {
				t.Stop()

				for _, h := range handlers.Get() {
					h()
				}

				os.Exit(int(atomic.LoadInt64(&exitCode)))
			}
		}
	}()
}

// A exit function that allow defers in main function
func Exit(code int) {
	atomic.StoreInt64(&exitCode, int64(code))

	runtime.Goexit()
}

func AtExit(handler func()) {
	handlers.Add(handler)
}