[zeromq-dev] On hooking memory allocations

Tue Nov 29 11:51:03 CET 2016

That works on Linux (and I guess *NIX) yes, but I'm not sure if Windows
has a similar functionality. Even if it does, the use case here (a game
engine/library) is most likely a statically linked binary, so I think it
won't work there :-)

All in all this is an interesting discussion, but let's see some PRs and
take it from there :-)

On Mon, 2016-11-28 at 11:48 -0800, Max Kozlovsky wrote:
> Each program can be linked with a separate malloc implementation if the
> user so desires. Libraries don't need to be aware which implementation it
> is. Different malloc implementation can be even substituted at run time on
> platforms with dynamic linking support (LD_PRELOAD etc).
> 
> On Mon, Nov 28, 2016 at 11:39 AM, Jens Auer <jens.auer at betaversion.net>
> wrote:
> 
> > Hi,
> >
> >
> >
> > yes and no. If you overwrite it globally at compute-time every program on
> > the system has to use your custom implementation. So if you deliver your
> > ZeroMQ library with your program it will work, but what if my program wants
> > a different custom allocator?
> >
> >
> >
> > Cheers,
> >
> > Jens
> >
> >
> >
> > *Von:* zeromq-dev [mailto:zeromq-dev-bounces at lists.zeromq.org] *Im
> > Auftrag von *Max Kozlovsky
> > *Gesendet:* Montag, 28. November 2016 20:36
> > *An:* ZeroMQ development list
> > *Betreff:* Re: [zeromq-dev] On hooking memory allocations
> >
> >
> >
> > Hi,
> >
> >
> >
> > Would not globally overwriting malloc/free with the custom implementation
> > achieve the desired behavior (instead of providing hooks for installing
> > malloc overrides in each and every library)?
> >
> >
> >
> > Max
> >
> >
> >
> > On Mon, Nov 28, 2016 at 5:08 AM, Auer, Jens <jens.auer at cgi.com> wrote:
> >
> > Hi,
> >
> > I don't see a big problem with the C API except that C doesn't support
> > overloads. So if the function has a new name, e.g.
> > zmq_ctx_new_with_allocator, everything stays plain C. The default instance
> > would be a
> >
> > static void* malloc_(size_t n, void*) {return malloc(n);}
> > static void free_(void* ptr, size_t n, void*) {free(ptr);}
> >
> > allocator_t alloc{
> > NULL,
> > malloc_,
> > free_
> > };
> >
> > context_t then stores the member and gets methods to forward memory
> > allocations to the function pointers, passing the hint pointer as an
> > additional argument.
> >
> > In my C++ code, I can then use an allocator
> > static void* allocate(size_t n, void* obj) {return
> > static_cast<std::allocator<char>>(obj)->allocate(n); }
> > static void free_(void* ptr, size_t n, void*obj) {
> > static_cast<std::allocator<char>>(obj)->deallocate(ptr, n); }
> >
> > std::allocator<char> a;
> > allocator_t zmqAlloc{
> >    &a,
> >    allocate,
> >    free_
> > };
> >
> > void* ctx = zmq_ctx_new_with_allocator(&zmqAlloc);
> >
> > I think this should work?
> >
> > Best wishes,
> > Jens
> >
> > --
> > Dr. Jens Auer | CGI | Software Engineer
> > CGI Deutschland Ltd. & Co. KG
> > Rheinstraße 95 | 64295 Darmstadt | Germany
> > T: +49 6151 36860 154
> > jens.auer at cgi.com
> > Unsere Pflichtangaben gemäß § 35a GmbHG / §§ 161, 125a HGB finden Sie
> > unter de.cgi.com/pflichtangaben.
> >
> > CONFIDENTIALITY NOTICE: Proprietary/Confidential information belonging to
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> >
> > > -----Original Message-----
> > > From: zeromq-dev [mailto:zeromq-dev-bounces at lists.zeromq.org] On Behalf
> > Of
> > > Luca Boccassi
> > > Sent: 28 November 2016 12:30
> > > To: ZeroMQ development list
> > > Subject: Re: [zeromq-dev] On hooking memory allocations
> > >
> > > That would work for an internal API, but given we expose a C API
> > unfortunately I
> > > don't think that would work as a public API :-( And I think for this use
> > case they
> > > would require a public API.
> > >
> > > As an external API, a new zmq_ctx_set that takes a callback would have
> > been ideal,
> > > but it only takes int. So perhaps a new zmq_ctx_set_allocator that takes
> > a callback
> > > pointer would be the next best.
> > >
> > > An alternative would be to have a system similar to what we use for the
> > poll
> > > implementation (epoll kqueue select etc), but this would be a build-time
> > option,
> > > and the implementation would have to be checked in, which I don't think
> > is an
> > > option for this case, right?
> > >
> > > On Mon, 2016-11-28 at 10:51 +0000, Auer, Jens wrote:
> > > > Hi,
> > > >
> > > > I am just a user, but I would love to see this change. I have thinking
> > > > about this and I would like to be able to pass a C++ allocator object
> > > > to ZeroMQ, so a simple function hook is not enough. My idea is to
> > > > define a struct in the interface
> > > >
> > > > struct allocator_t
> > > > {
> > > >     void* hint;
> > > >     void* (allocate)(size_t, void*);
> > > >     void (deallocate)(void*, size_t, void*); };
> > > >
> > > > and store this in the context object. Since I don't think that this
> > should be
> > > changed during runtime, I would create a new zmq_ctx_new overload which
> > takes a
> > > parameter of type allocator_t. The default value would be to call
> > malloc/free.
> > > >
> > > > Cheers,
> > > > Jens
> > > >
> > > > --
> > > > Jens Auer | CGI | Software-Engineer
> > > > CGI (Germany) GmbH & Co. KG
> > > > Rheinstraße 95 | 64295 Darmstadt | Germany
> > > > T: +49 6151 36860 154
> > > > jens.auer at cgi.com<mailto:jens.auer at cgi.com>
> > > > Unsere Pflichtangaben gemäß § 35a GmbHG / §§ 161, 125a HGB finden Sie
> > unter
> > > de.cgi.com/pflichtangaben<http://de.cgi.com/pflichtangaben>.
> > > >
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> > > > ________________________________
> > > > Von: zeromq-dev [zeromq-dev-bounces at lists.zeromq.org]" im Auftrag von
> > > > "Petteri Salo [petteri.salo at gmail.com]
> > > > Gesendet: Montag, 28. November 2016 09:40
> > > > An: zeromq-dev at lists.zeromq.org
> > > > Betreff: [zeromq-dev] On hooking memory allocations
> > > >
> > > > Hello,
> > > >
> > > > Let me first do a little introduction as I'm new to this list. I'm a
> > software engineer
> > > with 15+ years of experience working on games at a company called Remedy
> > > Entertainment Ltd. We've done games for PC, and various games consoles
> > over the
> > > years. Most recently we did Quantum Break for Xbox One.
> > > >
> > > > I've now been tasked with evaluating ZeroMQ. One important feature of
> > any
> > > library we use in games is the ability to hook all memory allocations -
> > this is to allow
> > > the use of custom memory allocators and/or for tracking when and where
> > memory is
> > > allocated.
> > > >
> > > > I've searched the libzmq source code and there is about 150 uses of
> > new, malloc,
> > > realloc , etc.
> > > >
> > > > If we were to adopt libzmq we'd like to put in allocation hooks and
> > that work
> > > would then be something that we'd like to contribute back to the
> > project. Having
> > > those hooks in the main repository would then make it easier for us to
> > adopt future
> > > changes to the library.
> > > >
> > > > So, my question is would this kind of change be something that would be
> > > accepted? Of course assuming that coding conventions, proper way of
> > submitting
> > > the patch etc. are followed. I do realize that one would want to see the
> > actual code
> > > before accepting. I'm interested in the principle of accepting a change
> > such as this,
> > > since it would introduce a new "rule" for working ión libzmq source code
> > : "All
> > > allocations shall go through an allocation hook."
> > > >
> > > > Best Regards,
> > > >
> > > > Petteri Salo
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