[zeromq-dev] Polling Question

Christoph Heindl christoph.heindl at gmail.com
Sun Mar 24 10:59:35 CET 2013


I've been working on a simple application where a server sends images over
networks to clients. It works great, except that I can see 'lags' from time
to time of up to 5 seconds on the client side and I'm unsure what causes
this behaviour. Note that I'm running the application on the same machine
(localhost) on windows 7 using ZMQ 3.2.2.

I'm currently providing two operating modes:
 - fast mode (PUB/SUB)
 - and a kind of reliable mode where the client first needs to send a ready
flag before acks with the image.

For both modes I'm providing timeouts on the client side. These timeouts
are based on ZMQ poll.

When using the mode and a lag occurs (the poll is the blocking function)
the server happilies continues to publish images as expected. Depending on
the HWM set for outgoing messages on the server side, the server either
starts to drop images or fills up the memory. The client side just blocks
until the timeout occurs. It does not seem that memory at the client side
rises dramatically.

When using the reliable mode and a lag occurs (again the poll is the
blocking function) the server stops publishing images until the next client
ready flag is encountered (which can last for a couple of seconds). This
can't be due to full queues, can it?

I've tested this on numerous machines (all Win 7) and I'm puzzled of what
can cause such a behaviour.

Any ideas?

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