Do I need to worry about this race condition?

[Art Mellor]

I have a race condition that is clearly real. I don't think it will cause a problem, but I wanted to make sure I'm not missing something non-obvious, either in a side-effect or in a better way to do it.

Below is a stripped down toy version of what I'm working with, I also have it in the playground. The race condition output is below the code listing.

Basically, I'm swapping out a func in a var to turn debug output on/off. My thoughts are that the assignment is "atomic" and thus I'm not at risk for unexpected behavior. I realize I could embed it in a struct with appropriate methods and a lock, but I like having it behave as a straight func.

http://play.golang.org/p/pqWOmUP13I

(obviously running it in the playground won't show the -race output)

It's a go routine printing debug output and a main routine turning the debug on and off.

Is there something bad possibly happening that I'm missing or a better way to do this. I also like having clean -race output.

Thanks!

package main

import (
    "fmt"
    "time"
)

func DebugOn(fmtstr string, args ...interface{}) {
    fmt.Printf(fmtstr, args...)
    return
}

func DebugOff(fmtstr string, args ...interface{}) {
    return
}

var Debug = DebugOn

func main() {

    go func() {
        for i := 1; i <= 100; i++ {
            Debug("%03d: Debug\n", i)
            time.Sleep(100 * time.Millisecond)
        }
    }()

    for i := 1; i <= 5; i++ {
        time.Sleep(1 * time.Second)
        Debug = DebugOff
        time.Sleep(1 * time.Second)
 Debug = DebugOn
    }

    return
}

/*
==================
WARNING: DATA RACE
Write by main goroutine:
  main.main()
      /emu/build/art/repo/Go/src/race/race.go:30 +0x6c

Previous read by goroutine 5:
  main.func-001()
      /emu/build/art/repo/Go/src/race/race.go:23 +0xf1

Goroutine 5 (running) created at:
  main.main()
      /emu/build/art/repo/Go/src/race/race.go:26 +0x37
==================
*/

[Brad Fitzpatrick]

Once you have any race, all bets are off. There is no such thing as a benign race.

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[Tamás Gulácsi]

There's no such thing as benign data race: https://software.intel.com/en-us/blogs/2013/01/06/benign-data-races-what-could-possibly-go-wrong

So guard it with a muted - you can hide the muted into a function, if you wish.

[Art Mellor]

Thanks for the pointer to that article - just what I needed.

Also, hadn't thought of wrapping the func in a func to hide the mutex. Great idea.

On Sunday, April 19, 2015 at 9:19:20 AM UTC-5, Tamás Gulácsi wrote:

[atd...@gmail.com]

Perhaps something like that can help:

http://play.golang.org/p/o8-Jy42aPP

[Art Mellor]

I literally just completed writing almost the exact code, although yours is slightly more elegant - so I'll steal that.

Thanks - exactly what I was looking for!

[John Waycott]

Here's another take, more like your original idea of swapping functions:

https://play.golang.org/p/912MwiNFf1

It would be useful if you wanted to swap out different types of debug functions.

[atd...@gmail.com]

A bit cleaner of an example, (added the possibility to provide an alternate logging function as John mentioned it could be useful)

http://play.golang.org/p/FaDIzeBc9t