[zeromq-dev] Zero-copy and INPROC transport

[Wenzel Jakob]

Dear Charles,

this page notes that the creation of the message itself is guaranteed not to cause a copy operation.

It does not, however, say anything about moving the message from one socket to the other, and about the behavior of zmq_recvmsg.

(My question is thus if the zero-copy guarantee applies to the whole chain of operations.)

Thank you,
Wenzel

> On Jan 16, 2016, at 5:20 PM, Charles Remes <lists at chuckremes.com> wrote:
> 
> Look at this man page:
> 
> http://api.zeromq.org/3-2:zmq-msg-init-data <http://api.zeromq.org/3-2:zmq-msg-init-data>
> 
> Zeromq does zero copy.
> 
> However, before you go and write a bunch of complex code, just use the normal facilities first and benchmark it. You may not need to do this extra work.
> 
> 
>> On Jan 16, 2016, at 10:13, Wenzel Jakob <wenzel at inf.ethz.ch <mailto:wenzel at inf.ethz.ch>> wrote:
>> 
>> Hello all,
>> 
>> I’m interested in using ZeroMQ to build a multithreaded application which uses INPROC transport to propagate messages between threads.
>> 
>> My plan was to send messages using zmq_sendmsg (created using zmq_msg_init_data with a custom deallocator), and to receive messages, I was planning to use zmq_recvmsg.
>> 
>> I’m concerned if INPROC will perform unnecessary copies of messages, which can be very large in my application (i.e. hundreds of megabytes). In principle, it should just be possible to do it without copies by just moving zmq_msg_t* from the inproc socket of one thread to that of the other — however, I am not familiar enough with the implementation of ZeroMQ to know if that is indeed what happens. Can anyone here advise?
>> 
>> Thank you in advance for your help!
>> 
>> Best regards,
>> Wenzel
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