[zeromq-dev] ZeroMQ 4.2 release, planning

[Doron Somech]

Sorry for the late response, increasing the msg_t structure will be
great, however this will require changing a lot of binding.

Sorry for disappearing, baby and full time job is a lot :-), hopefully
I'm back...




On Mon, Aug 29, 2016 at 6:46 PM, Luca Boccassi <luca.boccassi at gmail.com> wrote:
> Sorry, I meant if we go with (1), not (2), we might bump the size as
> well, since we are already doing another ABI-breaking change.
>
> I agree on the solution as well.
>
> On Mon, 2016-08-29 at 17:12 +0200, Pieter Hintjens wrote:
>> I'm confused between the (1) and (2) choices, and can't see where
>> bumping the message size fits.
>>
>> Nonetheless, I think bumping the size, fixing the alignment issues,
>> and bumping the ABI version is the best solution here.
>>
>> On Fri, Aug 26, 2016 at 12:33 PM, Luca Boccassi <luca.boccassi at gmail.com> wrote:
>> > I've given some more thoughts and testing to the alignment issue. I can
>> > reproduce the problem by enabling alignment checks on x86 too.
>> >
>> > But most importantly, I think we cannot get away from bumping the ABI
>> > with this fix, however we rearrange it, simply because applications need
>> > to be rebuilt against the new header to be fixed. A simple rebuild of
>> > the libzmq.so is not enough. And the way to do this is to bump the ABI
>> > so that distros can schedule transitions and rebuilds and so on.
>> >
>> > So the choice list is now restricted to:
>> >
>> > 1) Bump ABI
>> > 2) Revert the fix and leave everything broken on sparc64 and some
>> > aarch64 (rpi3 seems not to be affected, must depend on the SoC flavour)
>> >
>> > If we go with 2, we might as well get 2 birds with one stone and bump
>> > the zmq_msg_t size to 128 as we have talked about in the past.
>> >
>> > Doron, this would help with the new UDP based socket types right?
>> >
>> > Pros of bumping msg size:
>> >
>> > - we can get rid of the malloc() in the lmsg type case as all the data
>> > will fit
>> >
>> > Cons:
>> >
>> > - for the vsm/cmsg type cases (for most architectures anyway) it won't
>> > fit anymore into a single cacheline
>> >
>> > Given all this, I'd say we should go for it.
>> >
>> > Opinions?
>> >
>> > On Sat, 2016-08-13 at 16:59 +0100, Luca Boccassi wrote:
>> >> Hello,
>> >>
>> >> Trying to give some thoughts again on the libzmq 4.2 release. It's
>> >> really long overdue!
>> >>
>> >> The main issue from my point of view is this change:
>> >>
>> >> https://github.com/zeromq/libzmq/commit/d9fb1d36ff2008966af538f722a1f4ab158dbf64
>> >>
>> >> -typedef struct zmq_msg_t {unsigned char _ [64];} zmq_msg_t;
>> >>  +/* union here ensures correct alignment on architectures that require
>> >> it, e.g.
>> >>  + * SPARC
>> >>  + */
>> >>  +typedef union zmq_msg_t {unsigned char _ [64]; void *p; } zmq_msg_t;
>> >>
>> >>
>> >> This is flagged by the common ABI checkers tools as an ABI breakage
>> >> (see: http://abi-laboratory.pro/tracker/timeline/zeromq/ ). And it makes
>> >> sense from this point of view: if some applications on some
>> >> architectures are broken due to wrong alignment, they would need to be
>> >> rebuilt, and the way to ensure that is to bump the ABI "current" digit
>> >> to make sure maintainers do a rebuild.
>> >>
>> >> On the other hand, signaling an ABI breakage is a pain, and a cause of
>> >> major churn for packagers and maintainers. It means for example a new
>> >> package has to be created (eg: libzmq5 -> libzmq6), and a transition has
>> >> to be started and all reverse dependencies need to be rebuilt. And if
>> >> this is pointless for all save a few corner cases (eg SPARC64 as for
>> >> above) it's all quite frustrating.
>> >>
>> >> So we have a choice to make before we release 4.2, four possibilities as
>> >> far as I can see:
>> >>
>> >> 1) Ignore the ABI checkers and get yelled at by maintainers and
>> >> packagers. Also the SPARC64 users will most likely NOT get their bug
>> >> fixed
>> >> 2) Bump ABI revision to 6 and get yelled at by maintainers and packagers
>> >> 3) Revert the above change and postpone it to when we have a more
>> >> generally useful reason to break ABI (bump zmq_msg_t from 64 to 128
>> >> bytes for example, Doron?)
>> >> 4) Try to be clever and revert the above change and use something like
>> >> #pragma pack(8). This will fool the ABI checkers (I tried it), and given
>> >> that typedef is only used externally to allocate the right size it
>> >> shouldn't actually affect anything, apart from the users of SPARC64
>> >> which should get the bugfix with this too. This is very sneaky :-)
>> >>
>> >> CC'ing Lazslo, the Debian maintainer, given what we choose to do might
>> >> result in a lot of work for him :-)
>> >>
>> >> Opinions?
>> >>
>> >> Kind regards,
>> >> Luca Boccassi
>> >>
>> >> On Tue, 2016-05-03 at 10:39 +0200, Pieter Hintjens wrote:
>> >> > Hi all,
>> >> >
>> >> > I'm just throwing some ideas on the table. We have a good package of
>> >> > work on master and it's probably time to make a 4.2 release.
>> >> >
>> >> > Luca has already back-ported the enable/disable draft design from
>> >> > zproject (CZMQ et al). Yay! So we can now release stable master
>> >> > safely, while continuing to refine and extend the draft API sections.
>> >> >
>> >> > I propose:
>> >> >
>> >> > - to end with the stable fork policy; this was needed years ago when
>> >> > we had massively unstable masters. It's no longer a problem.
>> >> > - to use the github release function for libzmq releases and deprecate
>> >> > the separate delivery of tarballs.
>> >> > - we aim to make a 4.2.0 rc asap, then fix any issues we get, with
>> >> > patch releases as usual.
>> >> > - we backport the release function to older maintained releases (4.1,
>> >> > 3.2) so that their tarballs are provided by github instead of
>> >> > downloads.zeromq.org.
>> >> >
>> >> > Problems:
>> >> >
>> >> > - this will break a few things that depend on downloads.zeromq.org. To
>> >> > be fixed as we go.
>> >> > - github tarballs are not identical to source tarballs, particularly
>> >> > they lack `configure`. I propose changing our autotools build
>> >> > instructions so they always start with `./autogen,sh` no matter where
>> >> > the sources come from.
>> >> >
>> >> > I think this will work and also let us gracefully deprecate/switch off
>> >> > the downloads box.
>> >> >
>> >> > -Pieter
>> >> > _______________________________________________
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>> >>
>> >>
>> >
>> >
>> >
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