[zeromq-dev] ZeroMQ 4.2 release, planning

[Pieter Hintjens]

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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