[zeromq-dev] Inter thread communication for scalability

Tue Jan 14 21:48:34 CET 2014

A visit to the Boost libraries reveals there's a brand-new Boost.Lockfree
library that must have arrived with one of the last few versions. You
should seriously consider simply replacing your std::lists with
boost::lockfree::queues using your existing logic, and see if that gives
you the performance you're looking for before you make any massive changes.

On Tue, Jan 14, 2014 at 3:40 PM, Lindley French <lindleyf at gmail.com> wrote:

> I'm going to caution you about passing pointers through inproc. It may be
> possible to do safely, but I haven't yet figured out how to manage
> ownership semantics in an environment where messages (pointers) can be
> silently dropped.
>
> I didn't imagine serialization would be a problem since you referred to
> "buffers"; I thought these would be raw byte buffers. If you actually mean
> lists of objects, then yes, you'll need to serialize to use inproc. There
> are a number of options for serialization in C++; there's
> Boost.Serialization, Google Protobufs, a few others. You can also do it
> manually if your objects are simple.
>
> Qt Signals & Slots is another solution for inter-thread communication
> similar to inproc which has the expected C++ object semantics and therefore
> doesn't require serialization. The downside is it's really only useful for
> one-to-one, one-to-many, or many-to-one semantics. This covers a lot, but I
> don't think it has a way to cover one-to-any, which is really what you want
> (and what the zmq push socket is designed for).
>
>
> On Tue, Jan 14, 2014 at 2:42 PM, Kenneth Adam Miller <
> kennethadammiller at gmail.com> wrote:
>
>> Yeah, it's in C/++.
>>
>>
>> On Tue, Jan 14, 2014 at 1:39 PM, Charles Remes <lists at chuckremes.com>wrote:
>>
>>> If you are doing this from C and can access the raw memory, an inproc
>>> socket can pass pointers around. If you are using a managed language or one
>>> where accessing raw memory is difficult, you’ll want to figure out how to
>>> “fake” passing a pointer (or an object reference). In your case it seems
>>> like serializing/deserializing would be a big performance hit. That said,
>>> if that is the direction you must go then pick something fast like msgpack
>>> as your serializer.
>>>
>>>
>>> On Jan 14, 2014, at 1:29 PM, Kenneth Adam Miller <
>>> kennethadammiller at gmail.com> wrote:
>>>
>>> @AJ No, but I understand exactly why you suggested that. It's because I
>>> haven't explained that thread 1 is doing critical work and it needs to
>>> offload tasks to other threads as quickly as possible.
>>>
>>> @Lindley, Thanks so much for helping me see the truth! I was getting
>>> awful confused considering all the different bolony that could go on if I
>>> was stuck with semaphores, and I couldn't really re-envision it. Is there
>>> any kind of convenience function or core utility for de-serializing the
>>> data you receive over inproc messages?
>>>
>>>
>>> On Tue, Jan 14, 2014 at 12:49 PM, AJ Lewis <aj.lewis at quantum.com> wrote:
>>>
>>>> In the zeromq example, couldn't you just skip thread 1 entirely?  Then
>>>> the
>>>> PULL socket from thread 2 takes uncompressed input from the source,
>>>> compresses it, and shoves it out the PUSH socket to thread 3 for output.
>>>>
>>>> In this case, the PULL socket is the uncompressed pool and the PUSH
>>>> socket
>>>> is the compressed pool.  Just make sure your uncompressed pool doesn't
>>>> fill
>>>> up faster than thread 2 can compress it, or you'll need to implement
>>>> some
>>>> logic to prevent it from using up all the memory.
>>>>
>>>> AJ
>>>>
>>>> On Tue, Jan 14, 2014 at 01:16:32PM -0500, Lindley French wrote:
>>>> > In this case your "buffers" are really just messages, aren't they? A
>>>> thread
>>>> > grabs one (receives a message), processes it, and writes the result
>>>> into
>>>> > another buffer (sends a message).
>>>> >
>>>> > The hard part is that ZeroMQ sockets don't like to be touched by
>>>> multiple
>>>> > threads, which complicates the many-to-many pattern you have going
>>>> here.
>>>> > I'm no expert, but I would suggest....
>>>> >
>>>> > Each "pool", A and B, becomes a single thread with two ZMQ inproc
>>>> sockets,
>>>> > one push and one pull. These are both bound to well-known endpoints.
>>>> All
>>>> > the thread does is continually shove messages from the pull socket to
>>>> the
>>>> > push socket.
>>>> >
>>>> > Each thread in "Thread set 1" has a push inproc socket connected to
>>>> pool
>>>> > A's pull socket.
>>>> >
>>>> > Each thread in "Thread set 2" has a pull inproc socket connected to
>>>> pool
>>>> > A's push socket and a push inproc socket connected to pool B's pull
>>>> socket.
>>>> > For each message it receives, it just processes it and spits it out
>>>> the
>>>> > other socket.
>>>> >
>>>> > The thread in "Thread set 3" has a pull inproc socket connected to
>>>> pool B's
>>>> > push socket. It just continually receives messages and outputs them.
>>>> >
>>>> > This may seem complicated because concepts that were distinct before
>>>> > (buffer pools and worker threads) are now the same thing: they're
>>>> both just
>>>> > threads with sockets. The critical difference is that the "buffer
>>>> pools"
>>>> > bind to well-known endpoints, so you can only have a few of them,
>>>> while the
>>>> > worker threads connect to those well-known endpoints, so you can have
>>>> as
>>>> > many as you like.
>>>> >
>>>> > Will this perform as well as your current code? I don't know. Profile
>>>> it
>>>> > and find out.
>>>> >
>>>> >
>>>> > On Tue, Jan 14, 2014 at 12:23 PM, Kenneth Adam Miller <
>>>> > kennethadammiller at gmail.com> wrote:
>>>> >
>>>> > > So, I have two pools of shared buffers; pool A, which is a set of
>>>> buffers
>>>> > > of uncompressed data, and pool B, for compressed data. I three sets
>>>> of
>>>> > > threads.
>>>> > >
>>>> > > Thread set 1 pulls from pool A, and fills buffers it receives from
>>>> pool A
>>>> > > up with uncompressed data.
>>>> > >
>>>> > > Thread set 2 is given a pool from A that has recently been filled.
>>>> It
>>>> > > pulls a buffer from pool B, compresses from A into B, and then
>>>> returns the
>>>> > > buffer it was given, cleared, back to pool A.
>>>> > >
>>>> > > Thread set 3 is a single thread, that is continually handed
>>>> compressed
>>>> > > data from thread set 2, which it outputs. When data is finished
>>>> output, it
>>>> > > returns the buffer to pool B, cleared.
>>>> > >
>>>> > > Can anybody describe a scheme to me that will allow thread sets 1 &
>>>> 2 to
>>>> > > scale?
>>>> > >
>>>> > > Also, suppose for pools A and B, I'm using shared queues that are
>>>> just C++
>>>> > > stl lists. When I pop from the front, I use a lock for removal to
>>>> make sure
>>>> > > that removal is deterministic. When I enqueue, I use a separate
>>>> lock to
>>>> > > ensure that the internals of the STL list is respected (don't want
>>>> two
>>>> > > threads receiving iterators to the same beginning node, that would
>>>> probably
>>>> > > corrupt the container or cause data loss, or both). Is this the
>>>> appropriate
>>>> > > way to go about it? Thread sets 1 & 2 will likely have more than one
>>>> > > thread, but there's no guarantee that thread sets 1 & 2 will have
>>>> equal
>>>> > > threads.
>>>> > >
>>>> > > I was reading the ZeroMQ manual, and I read the part about
>>>> multi-threading
>>>> > > and message passing, and I was wondering what approaches should be
>>>> taken
>>>> > > with message passing when data is inherently shared between threads.
>>>> > >
>>>> > > _______________________________________________
>>>> > > zeromq-dev mailing list
>>>> > > zeromq-dev at lists.zeromq.org
>>>> > > http://lists.zeromq.org/mailman/listinfo/zeromq-dev
>>>> > >
>>>> > >
>>>>
>>>> > _______________________________________________
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>>>> > zeromq-dev at lists.zeromq.org
>>>> > http://lists.zeromq.org/mailman/listinfo/zeromq-dev
>>>>
>>>>
>>>> --
>>>> AJ Lewis
>>>> Software Engineer
>>>> Quantum Corporation
>>>>
>>>> Work:    651 688-4346
>>>> email:   aj.lewis at quantum.com
>>>>
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>>
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