2018-07-04 7:26 GMT+02:00 Christopher Sean Morrison via brlcad-devel <
brlcad-devel@lists.sourceforge.net>:
>
> On Jun 27, 2018, at 12:36 PM, Daniel Roßberg <danielmrossb...@gmail.com>
> wrote:
>
> Is the Tk-mged supposed to work with multiple threads? It looks like if a
> simple call to bu_log() in a subthread can crash it.
>
>
> It is supposed to work, but that’s been historically tricky code to get
> right and keep working because of how libbu manages a set of global locks.
> Currently, nearly everything goes through BU_SEM_SYSCALL which means you
> can’t recursively call bu functions from bu functions safely without
> hitting a deadlock, race, or other issue. This is particularly problematic
> for bu_log() and it’s hook functions (which very often are written to call
> bu functions, but that’s nfg) and bu_malloc() and friends.
>
> What’s needed is breaking up BU_SEM_SYSCALL into different semaphores for
> each of the respective bu groupings that need to coordinate some access.
>
I'm afraid there is an additional issue with calling Tk functions: In
general, Tk functions have to be called all from the same thread because
they use thread specific memory. See e.g. this thread:
https://sourceforge.net/p/tktoolkit/bugs/1359/
And, this was the reason why we see crashes with
check_overlaps: Tk_FreeGC() calls TkGetDisplay() which looks at thread
specific data, can't find anything there, and returned NULL
which Tk_FreeGC() tries to dereferenciate. According to the above mentioned
discussion, there are specific Tcl/Tk APIs for queuing events from one
thread into another, which would be necessary to use in a multi thread
Tk-mged.
Regards,
Daniel
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