On Thu, Apr 17, 2014 at 10:54:59PM +0200, Michael Haberler wrote:
> Goswin,
>
> Am 17.04.2014 um 11:24 schrieb Goswin von Brederlow <[email protected]>:
>
> > On Wed, Apr 16, 2014 at 08:07:27PM +0200, Michael Haberler wrote:
> >> we're using zeroMQ in machinekit (formerly LinuxCNC)
> >>
> >> to retain the end-to-end principle, we need to be able to send multipart
> >> messages to and from RT threads
> >>
> >> that isnt possible with libzmq code since it's C++ and uses dynamic memory
> >> allocation
> >>
> >> the code which we'll be using is based on a lock-free ringbuffer in shared
> >> memory (ring_*), and a multipart framing layer on top of that (bring_*):
> >> http://psha.org.ru/cgit/psha/ring/?h=wip-buffer
> >>
> >> a proxy thread at the RT boundary translates from zmq to ringbuffer
> >> framing and back
> >>
> >> just in case somebody has a similar requirement
> >>
> >> - Michael
> >
> > doesn't zero-copy fix that?
>
> I dont understand what are you are suggesting, could you elaborate?
>
> - Michael
You have your data in some buffer somewhere in memory. Then when you
can call zmq_msg_init_data() to make a message out of it without
copying the data:
The zmq_msg_init_data() function shall initialise the message object
referenced by msg to represent the content referenced by the buffer
located at address data, size bytes long. No copy of data shall be
performed and ØMQ shall take ownership of the supplied buffer.
If provided, the deallocation function ffn shall be called once the
data buffer is no longer required by ØMQ, with the data and hint
arguments supplied to zmq_msg_init_data().
The deallocation function allows you to reuse buffers that zmq has
finished with so you don't need to dynamically allocate them. And the
data isn't copied so the zmq_msg functions run in constant time no
matter how large the buffer.
MfG
Goswin
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