[zeromq-dev] Thread safe Pub/Sub and Multicast

Pieter Hintjens ph at imatix.com
Wed Mar 16 11:06:44 CET 2016


Off-topic, but I need to ask, how do you do the syntax highlighting in emails?

On Mon, Mar 14, 2016 at 4:42 PM, MinRK <benjaminrk at gmail.com> wrote:
> On Sat, Mar 12, 2016 at 9:00 PM, Dave Kuhlman <dkuhlman at davekuhlman.org>
> wrote:
>>
>> For those of us who use Python and the pyzmq library for ZeroMQ, I'm
>> wondering whether the solution to the problem and need for thread
>> safety is to avoid threads and to use either the tornado ioloop
>> support or asyncio ioloop.  Am I right that doing so would give a
>> Python developer the capabilities of multiple threads without the
>> worries about thread safety.
>>
>> One reason I'm asking is that I'm the one who added the ioloop
>> examples to zguide (in examples/Python/tornado_ioloop and
>> examples/Python/ascyncio_ioloop).  A number of those examples use
>> (what I understand as) multiple concurrent tasks within a single
>> thread.  So, I'm wondering whether that really is thread safe (or
>> whatever the equivalent is for tasks), as I believe it is.
>
> Yup, asyncio/tornado are single-threaded eventloops, so you won’t get
> threadsafety problems if everything happens in a callback/coroutine on those
> loops. You can also use these to make threadsafe actions, even when using
> actual threads. In the tornado case, there is one (and only one) threadsafe
> method, and it’s IOLoop.add_callback. You can use this to schedule calls to
> be made on the IOLoop, from other threads. For instance:
>
> loop = start_loop_in_background_thread()
>
> def threadsafe_send(socket, msg):
>     loop.add_callback(lambda : socket.send_multipart(msg))
>
> In this way, you can schedule sends from any number of threads perfectly
> safely, because the actual zmq socket is only ever operated on in the IO
> thread. Threadsafe recv is similarly doable, but a bit more code.
>
> On the other hand, you can also write coroutine-unsafe code if you have
> yields in the middle of sending multipart messages, for instance:
>
> @coroutine
> def bad_coroutine_send(socket, msg):
>     for frame in msg[:-1]:
>         yield socket.send(frame, zmq.SNDMORE)
>     yield socket.send(msg[-1])
>
> Where each yield is an opportunity to take over and do some other operation
> on the socket. I think it is a lot easier to write coroutine-safe code than
> thread-safe code, since all context switching is explicit (make sure you
> have no yield calls in the middle of an operation).
>
> -MinRK
>>
>>
>> Any enlightenment will be welcome.
>>
>> And, by the way, I suspect that something equivalent could be done
>> in Node.js (JavaScript), which also uses a single threaded approach
>> to "concurrency" (psuedo-concurrency, quasi-concurrency, whatever).
>> In Node.js, you could use callbacks, but there are libraries that
>> can wrap your code to make is seem more simple and parallel.  For
>> example, see async.js.  Here are a few quick examples from the
>> async.js Web page (https://www.npmjs.com/package/async):
>>
>>      async.map([`file1`,`file2`,`file3`], fs.stat, function(err, results){
>>          // results is now an array of stats for each file
>>      });
>>
>>      async.filter([`file1`,`file2`,`file3`], fs.exists, function(results){
>>          // results now equals an array of the existing files
>>      });
>>
>>      async.parallel([
>>          function(){ ... },
>>          function(){ ... }
>>      ], callback);
>>
>>      async.series([
>>          function(){ ... },
>>          function(){ ... }
>>      ]);
>>
>> As a bit of justification for this question, the main intension of
>> the Python ioloop support in tornado and asyncio is to address
>> problems of network and I/O delays and to enable our code to do
>> something useful during those delays.  That seems like a central
>> concern for users of ZeroMQ.
>>
>> Dave
>>
>>
>> On Sat, Mar 12, 2016 at 03:00:58AM +0200, Doron Somech wrote:
>> >    Hi All,
>> >    During the ZeroMQ hackathon I have added the Radio/Dish pattern
>> > (thread
>> >    safe version of pubsub) and multicast support (only for Radio/Dish
>> >    sockets) to both libzmq and czmq.
>> >    Radio/Dish is very similar to pub/sub with some differences:
>> >      * Thread safe, you can send and receive messages from multiple
>> >        threads, so for publisher you now don't need internal device to
>> >        publish from multiple threads and with subscriber you can use it
>> > as
>> >        load balancer.
>> >      * Only single frame can be sent
>> >      * Radio/Dish matching is exact matching (vs prefix of pubsub)
>> >      * Group (Radio/Dish topic) is string and currently limited to 15
>> >        chars (might be increased in the future)
>> >      * Group is set as part of the zmq_msg (libzmq) or zframe (czmq).
>> >      * You call join or leave on the socket (with methods instead of
>> >        socket options)
>> >
>> >    To learn how to use it with czmq take a loot at the following gist:
>> >    [1]https://gist.github.com/somdoron/9423196a228775c8f5af
>> >    For libzmq take a loot at the test:
>> >
>> > [2]https://github.com/zeromq/libzmq/blob/master/tests/test_radio_dish.c
>> >    pp#L90
>> >    And the most exciting news, with radio-dish you can use multicast
>> >    transport, just replace the address from following gist with udp
>> >    transport and multicast address, following is a valid address for
>> >    example:
>> >    udp://[3]239.0.0.1:55555
>> >    Regards
>> >    Doron
>> >
>> > References
>> >
>> >    1. https://gist.github.com/somdoron/9423196a228775c8f5af
>> >    2.
>> > https://github.com/zeromq/libzmq/blob/master/tests/test_radio_dish.cpp#L90
>> >    3. http://239.0.0.1:55555/
>>
>> > _______________________________________________
>> > zeromq-dev mailing list
>> > zeromq-dev at lists.zeromq.org
>> > http://lists.zeromq.org/mailman/listinfo/zeromq-dev
>>
>>
>> --
>>
>> Dave Kuhlman
>> http://www.davekuhlman.org
>> _______________________________________________
>> 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
>



More information about the zeromq-dev mailing list