"Andrea Grassi" <andreagrassi@sogeasoft.com> writes:
> In internet I searched for detailed specifications of poll/select system
> functions but I didn't understand one thing, that is which one of the 2
> statement is true:
> 1) poll/select wait only for FUTURE modifications of ready-read state of
> sockets
> 2) poll/select check if there is something to read at the moment of the call
> and otherwise wait for FUTURE modifications of ready-read state
#1 is nonsense. If poll worked like that, it would be impossible for
anyone to use it without suffering from race conditions. But if you
don't see where exactly the poll() specification says so, I observe
that it says first that poll sets the bit(s) if the requested condition
is true, and second that *if* none of the events have occurred yet,
poll should wait. See for instance
http://pubs.opengroup.org/onlinepubs/007908799/xsh/poll.html
regards, tom lane