Subject: Re: bug#29275: dynamic-link hangs on error

From: [email-masked] (Ludovic Courtès)
Date: Wed, 22 Nov 2017 16:47:57 +0100

Hello,

noxdafox <[email-masked]> skribis:

> GNU Guile 2.2.2
> Copyright (C) 1995-2017 Free Software Foundation, Inc.
>
> Guile comes with ABSOLUTELY NO WARRANTY; for details type `,show w'.
> This program is free software, and you are welcome to redistribute it
> under certain conditions; type `,show c' for details.
>
> Enter `,help' for help.
> scheme@(guile-user)> (use-modules (system foreign))
> scheme@(guile-user)> (define libc-obj (dynamic-link "nonexisting"))
> ERROR: In procedure dynamic-link:
> ERROR: In procedure dynamic-link: file: "nonexisting", message: "file
> not found"
>
> Entering a new prompt.  Type `,bt' for a backtrace or `,q' to continue.
> scheme@(guile-user) [1]> (define libc-obj (dynamic-link "nonexisting"))
>
> ^^^ here the VM becomes unresponsive.

This is because libguile synchronizes uses of ‘dynamic-link’ with a
non-recursive mutex.  Here, the “inner” ‘dynamic-link’ call occurs while
the mutex is already held by the calling thread, which is why it just
hangs.

Fixed in commit 48d42553ef5a9c2240bc2296d1b38dbfd5fca1ac, which will be
in the next 2.2 release.

Thanks,
Ludo’.