Asset loading race condition causes unexpected panic

[ViRb3]

I have a private project that uses go.rice. It works flawlessly on Windows, but on Linux, it fails with:

panic: could not locate box "assets"

It is compiled from the exact same source, on the same host (Windows 10), with the same Go toolchain (1.15). I started debugging go.rice, and noticed a very interesting race condition. I will simplify it below.

Intro

Recall the order in which Go initializes code: https://stackoverflow.com/questions/24790175/when-is-the-init-function-run

Say you have the following project:

rice-box.go

package main

import (
	"time"

	"github.com/GeertJohan/go.rice/embedded"
)

func init() {
    // ...
}

main.go

package main

import (
	rice "github.com/GeertJohan/go.rice"
	"log"
)

var box = rice.MustFindBox("assets")

func main() {
	log.Fatalln(box.String("message.txt"))
}

The issue

The first thing that will load is:

var box = rice.MustFindBox("assets")

Only then will rice-box.go be called, but by that time, the program will have panicked, because the assets box is not loaded. There are many additional ways this issue can be hit, including much less-trivial nested and multi-thread cases like in my private project.

Solution

The root of the problem is that the resource initialization is detached from the resource usage. Other projects such as binclude reference a variable in the generated file instead of global library functions in go-rice's case. You can reduce the amount of race cases in go-rice by making the resource initialize via a const/var instead of init() function, but ideally, a whole different approach should be employed.