function to execute entire functions with a locked mutex

withLock.go

// this script can be use to execute entire functions with a locked mutex.
// It is especially useful when a if statement needs to read from a mutex sensible variable.

// withLock accepts either a "func()" or a "func() interface{}"
// in the first case, it executes the function returining <nil>
// in the second case, it returns the value of the function as an interface{}

package main

import (
	"fmt"
	"sync"
)

var m = &sync.Mutex{}
var wg sync.WaitGroup

var tot int
var totlock int

func main() {
	for n := 0; n < 10000; n++ {
		wg.Add(2)
		go func() { tot++; wg.Done() }()
		go withLock(func() { totlock++; wg.Done() })
	}

	fmt.Println("without lock:\t", tot)
	fmt.Println("with lock:\t", totlock)

	// prints true
	fmt.Println(withLock(func() interface{} { return 1 == 1 }))
	// prints hello
	fmt.Println(withLock(func() interface{} { return "hello" }))

	// use as conditional
	if withLock(func() interface{} { return 1 == 1 }).(bool) {
		fmt.Println("if block")
	}

	// prints <nil>
	fmt.Println(withLock(func() bool { return false }))
	fmt.Println(withLock(func() (interface{}, interface{}) { return "a", "b" }))
}

func withLock(i interface{}) interface{} {
	m.Lock()
	defer m.Unlock()

	switch i.(type) {
	case func():
		i.(func())()
	case func() interface{}:
		return i.(func() interface{})()
	}

	return nil
}