Possible weird garbage collection bug, not sure - confused

[cerk]

Hi, I am running gothic on Windows (via Horkonaut fork). I am running into a weird problem. When I run the following program, I click on the "Hello World" button a few times. Then I wait 8+ minutes and click on the button about 10 times. Then I wait a minute or two and the program crashes with:

fatal error: unexpected signal during runtime execution
[signal 0xc0000005 code=0x0 addr=0xffffffffffffffff pc=0x40a057]

Note that if I turn off garbage collection, the program does not crash.

I have tried to strip the program down to a minimal form:

package main

import (
    // For Windows, "github.com/Horkonaut/gothic"
    "github.com/nsf/gothic"
    // Uncomment to prevent garbage collection and eliminate bug
    //"runtime/debug"
)

type bug struct {
    *gothic.Interpreter
}

func (b *bug) TCL_OnButtonPress() {
}

func main() {
    // Uncomment to prevent garbage collection and eliminate bug
    //debug.SetGCPercent(-1)
    ir := gothic.NewInterpreter(`
        wm title . PossibleBug      
        ttk::button .button -text {Hello World} -command go::OnButtonPress      
        pack .button
            `)

    ir.RegisterCommands("go", &bug{Interpreter: ir})
    <-ir.Done
}

Note that if I eliminate the "-command go::OnButtonPress" portion of the code, it does not crash either.

Could someone try to reproduce what I am seeing on a linux machine? Any ideas on what may be going on? It looks like there is some memory interaction between cgo and go that is causing a garbage collection crash.

I am running:

go1.3.2 windows/amd64
tcl8.6 on windows

Thanks for reading!

[nsf]

The key is to figure out what "unexpected signal" means on windows. Because on windows there are no posix signals. I'll take a look on it in few days.

[cerk]

I tried to do some research on the signal 0xc0000005 error on Windows, and all I could come up with is that it may be an access violation ("usually caused by heap memory corruption"):

http://stackoverflow.com/questions/5303524/what-exactly-is-the-scope-of-access-violation-0xc0000005

[nsf]

Interesting. I tried reproducing the issue on a linux machine, no luck. Will try it on windows tomorrow.

[nsf]

Also try using go 1.4.1, the latest go version, if possible. So that we stay in-sync here.

[cerk]

Just installed 1.4.1 and I am still getting the fatal error.

[nsf]

Yes, I can reproduce the issue on windows. I'll see what I can do to fix it within next few days (that is this week for sure).

[nsf]

Correction. Happend on linux too. So it's a bug in gothic I'm pretty much sure about it.

[nsf]

Here's the thing. I do a lot of nasty stuff in there. And it was written ages ago with a different Go runtime. I think I'll just rewrite everything following rsc's advice to never pass a Go pointer to C. It may take few more days to happen, but nothing really complicated, code is small after all.

Because it's really hard to say where it fails. Apparently my code doesn't play well with Go's precise GC.

[cerk]

Yes, I tried debugging what was happening myself (before filing this issue) but could not gain any traction with the error messages that were occurring. The only reason I found this issue was because I would leave a (larger) TclTk program running and then come back a half an hour later and press a button and it would crash mysteriously. I really appreciate you taking a look at it - and no rush on the fixes.

[nsf]

It seems to be fixed. I checked it only on linux, feel free to reopen issue if the bug is still there.

[cerk]

I checked it on Windows and it looks like you fixed it. Thanks!