[PATCH] libdw: add thread-safety to dwarf_getabbrev()
Sun Oct 27 18:11:00 GMT 2019
On Sun, Oct 27, 2019 at 09:59, Florian Weimer <firstname.lastname@example.org> wrote:
> * Mark Wielaard:
>>> Current glibc versions have a thread-local fast path, which should
>>> address some of these concerns. It's still not a bump-pointer
>>> allocator, but at least there are no atomics on that path.
>> Since which version of glibc is there a thread-local fast path?
> It was added in:
> commit d5c3fafc4307c9b7a4c7d5cb381fcdbfad340bcc
> Author: DJ Delorie <email@example.com <mailto:firstname.lastname@example.org>>
> Date: Thu Jul 6 13:37:30 2017 -0400
> Add per-thread cache to malloc
> So glibc 2.26. But it is a build-time option, enabled by default, but
> it can be switched off by distributions.
I doubt any non-mobile distros would disable it, the cost seems fairly
My main concern is that it seems like chunks will only enter the
thread-local cache in the presence of free()s (since they have to enter
the "smallbins" or "fastbins" first, and those two at a glance seem to
be filled very lazily or on free()); since the free()s are all on
dwarf_end this would pose an issue. I could also be entirely mistaken,
glibc is by no means a simple piece of code.
According to the comments, there might also be a 16 byte overhead per
allocation, which would explode the small allocations considerably.
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