[zeromq-dev] Inter thread communication for scalability

Tue Jan 14 22:19:54 CET 2014

Actually, which do you think would result in a better design decision?
Would using message passing result in a more scalable architecture? Where I
could just change a variable to increase throughput on better processors.

On Tue, Jan 14, 2014 at 3:09 PM, Kenneth Adam Miller <
kennethadammiller at gmail.com> wrote:

> Well, I'm just a type safety dork, so I tend to think that even losing
> type information over one pointer, even if I know where that pointer is
> going to end up what type it represents on the other side, is a bad thing.
> Plus it's a performance thing that's just unnecessary, but I don't think
> it's a big deal. These aren't objects, they are indeed raw buffers, as you
> assumed.
>
> Also, awesome about the boost find! Appreciate you so much, you are a
> beast. But I'm actually still in a sprint, so there's no version or commit
> with which these hypothetical discussions directly coincide, you're helping
> me get it right the first time.
>
>
> On Tue, Jan 14, 2014 at 2:48 PM, Lindley French <lindleyf at gmail.com>wrote:
>
>> 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
>>>>>> > >
>>>>>> > >
>>>>>>
>>>>>> > _______________________________________________
>>>>>> > zeromq-dev mailing list
>>>>>> > 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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