compatibility with apps using mallopt?

[Eric Wong]

Jason Evans <jasone at canonware.com> wrote:
> On Nov 17, 2013, at 2:47 PM, Eric Wong <normalperson at yhbt.net> wrote:
> > Hi, I'd like to continue providing the option of using jemalloc (and
> > other alternative malloc implementations) to glibc/Linux users of
> > cmogstored[1].
> > 
> > When I ./configure with LIBS=-ljemalloc, things go bad because the
> > mallopt call is still detected and going to glibc even though the glibc
> > malloc implementation is not used/linked.
> > 
> > So my question is: what's the best way to avoid mallopt() when using
> > glibc if cmogstored is linked to jemalloc (or any non-glibc malloc)?
> > 
> > Or should jemalloc provide a mallopt() function which may
> > wrap mallctl() in some cases and/or just do nothing at all?

> mallopt() is a non-standard function, as is jemalloc’s mallctl().  I
> contemplated what to do about mallopt(), mallinfo(), mallinfo_heap(),
> etc. while implementing mallctl(), and decided that trying to emulate
> them would be an exercise in futility.  As for replacing them, I would
> be uncomfortable having replacements do anything besides call
> abort(3).  I’ve never followed through with that though, because I’m
> afraid the cure might be worse than the disease.

Thanks for the response.  Is having mallopt() be a no-op acceptable to
you?  That would be acceptable to me.

> In the case of cmogstored, I suggest you conditionalize the mallopt()
> calls such that they’re only used when using glibc’s allocator.  Since
> you’re making an explicit effort to support multiple alternative
> memory allocators, you may end up adding other allocator-specific
> tuning in #if..#elif..#else..#endif blocks anyway.

I'm trying to conditionalize the build already, but the problem is that
mallopt detection succeeds with glibc even if I use LIBS=-ljemalloc (or
any alternative allocator).  So I'm wondering if there's a way to stop
mallopt detection if jemalloc is used on a GNU system.

I suppose I could use dlsym to find mallctl and use that as an indicator
jemalloc is linked into the process at runtime.  But maybe there's a
better way...