Nondeterministic bug in Chrome regarding (u)int64 values

[mibitzi]

Hi,
I am generating a json on my Backend which includes a time.Duration field and I am trying to unmarshal it in gopherjs:

Playground: http://www.gopherjs.org/play/#/kdIAc8hVfH

package main

import (
    "encoding/json"
    "time"

    "github.com/gopherjs/gopherjs/js"
)

type Player struct {
    Main time.Duration
}

func main() {
    for i := 0; i < 1000; i++ {
        raw := `{"Main":1200000000000}`
        out := &Player{}

        if err := json.Unmarshal([]byte(raw), out); err != nil {
            // This error occurs very often, but not always
            js.Global.Get("console").Call("error", err.Error())
        }
    }
}

From my tests this works without issues in firefox but in chromium there is an error about ~900 of 1000 times. So it does sometimes work, but most of the time there's an error.

I'm using Chromium Version 41.0.2272.101 (64-bit) on linux.

Edit:
Internet Explorer seems to work fine as well. And Google Chrome 41 on Windows has the same issue still.

[dmitshur]

Confirmed via playground link on Chrome 41.0.2272.101 on OS X. Seeing 880~920 errors per run. This is pretty bizarre.

Seeing zero errors in Firefox.

Here's a slightly modified version that shows total errors in the output box:

http://www.gopherjs.org/play/#/W9Ne2KyZSV

With it, I see that when the console is opened, I keep getting 900~ errors each time, but with console closed, I get 900~ errors first two runs, but 0 errors afterwards. o.o

[neelance]

Chrome's JS optimizer is quite aggressive and sometimes it does optimizations that are wrong. It is also not deterministic. I've seen similar issues before and will try to find a workaround.

[neelance]

I've tracked down the exact issue. Here is a JavaScript test case:

var f = function() {
  var a = 4294967295;
  var b = 0;
  var c = a + b;
  console.log(c, c >>> 0);
};

for (var i = 0; i < 1000; i++) {
  f();
}

After some iterations, c >>> 0 changes from 4294967295 to 0. This is a quite fundamental bug, I haven't found a workaround. Good news is that it seems to be fixed in the Chrome Canary version. So I guess we'll have to wait until the fix ships in the stable channel.

[mibitzi]

Nice. I guess then we can close this for now :)

[neelance]

Let's keep it open until the bug is resolved in Chrome stable, just for others who run into the same issue.

[neelance]

I am using Chrome stable (version 41) and Chrome Canary (version 43). Only version 41 shows the bug. Is there someone who has Chrome beta (version 42) installed? It's not that easy to switch between release channels without messing with your system.

[mibitzi]

I don't have 42, but I noticed that in Version 40.0.2214.111 (64-bit) the bug also does not exist.
So it seems only 41 and possibly 42 are affected.

[neelance]

Chrome 42 just got released on the stable channel and the bug is fixed. Yey! 🎉