select.select and socket.setblocking

Grant Edwards grante at visi.com
Tue Dec 30 21:41:17 CET 2008


On 2008-12-30, Francesco Bochicchio <bockman at virgilio.it> wrote:

> 3. AFAIK (sorry, I feel acronym-ly today ;), there is no difference in 
> select between blocking and non-blocking mode. The difference is in the
> recv (again, assuming that you use TCP as protocol, that is AF_INET, 
> SOCK_STREAM), which in the blocking case would wait to receive all the 
> bytes that you requested,

No, in blocking mode it will wait to receive _some_ data (1 or
more bytes).  The "requested" amount is strictly an upper
limit: recv won't return more than the requested number of
bytes, but it might return less.

In non-blocking mode, it will always return immediately, either
with some data, no data (other end closed), or an EAGAIN or
EWOULDBLOCK error (I forget which).

> [...] I myself tend to avoid using non-blocking sockets, since
> blocking sockets are much easier to handle...

That depends on whether you can tolerate blocking or not.  In
an event-loop, blocking is generally not allowed.

-- 
Grant



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