[zeromq-dev] feedback on proposed Context API addition

[john skaller]

On 09/02/2012, at 5:56 AM, Chuck Remes wrote:

> A user on irc (calvin) may post here (or on this thread) later. He popped into the channel asking about pinning a socket to a specific CPU. I pointed him at ZMQ_AFFINITY which is available through zmq_setsockopt(). However, as he pointed out, that only controls socket affinity with I/O threads which may still be scheduled on any CPU.
> 
> After a little back-and-forth, here's a proposal for an addition to the C API.
> 
> 	void *zmq_init_with_affinity (int io_threads, char* cpu_bitmask_buffer, size_t bitmask_len);

And, either ZMQ_AFFINITY should be modified to support the arbitrary length
bitmask OR a new tag be invented such as

		ZMQ_LONG_AFFINITY

Also, since this API would exclude thread_safety as it too is an additional context
construction option, it may be right to start thinking about

	zmq_setcontextopt

function that looks like

	zmq_setsokopt

[The interface in C is ugly in the extreme .. ]

> 
> Such a change would allow a programmer to create a context and specify which specific CPUs should have I/O threads pinned to them. We need to use a byte buffer to contain the bitmask and pass a length since systems with more than 64 CPUs and/or cores are already available.
> 
> This addition would not break existing code. Furthermore, we could implement zmq_init() internally with a call to zmq_init_with_affinity().

Not directly, my modification to the style guide prohibits this. You'd do it with
an inner function all the public interfaces called. Same effect though.

--
john skaller
skaller at users.sourceforge.net