[zeromq-dev] Non-blocking calls and Twisted

Martin Sustrik sustrik at 250bpm.com
Mon Apr 12 08:14:23 CEST 2010

Hi Laurens,

> I've noticed that 0MQ implementations are (at least the ones I've seen) 
> exclusively blocking connection per thread. Is there a particular reason 
> for this? I'd like to use Twisted and talk to 0MQ (from the role as a 
> publisher) asynchronously. Are there any important caveats there?

I am not 100% sure what you are asking about so let me give couple of 
answers and you pick the right one :)

1. zmq_send/zmq_recv calls are not necessarily blocking. Use ZMQ_NOBLOCK 
flag to make them non-blocking.

2. If you want to handle many physical connections at the same time, 0MQ 
is doing this under the hood. Single 0MQ socket can be backed by 10,000 
TCP connections.

3. If you still need multiple 0MQ sockets you can multiplex using 
zmq_poll() function.

4. If you want to multiplex between 0MQ sockets and POSIX sockets, you 
can still use zmq_poll().

5. If you still need to use native multiplexing mechanism, it's not 
possible. There's an explanation on FAQ page:

"Why can't I use standard I/O multiplexing functions such as select() or 
poll() on ØMQ sockets?"

"ØMQ socket is not a standard POSIX socket. It would be great if it was, 
however, POSIX doesn't provide a mechanism to simulate file descriptors 
in user space. To convert ØMQ sockets into POSIX file descriptors we 
would have either to move ØMQ to kernel-space or hack the kernel to 
provide the functionality needed. In both cases we would have to 
sacrifice portability and stick to a single operating system."


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