On Fri, 9 Dec 2005, Sybren Stuvel wrote:
Yves Glodt enlightened us with:
In detail I need a daemon on my central server which e.g. which in a
loop pings (not really ping but you know what I mean) each 20 seconds
one of the clients.
Do you mean pings one client every 20 sec, or each client every 20 sec?
You probably mean "really a ping, just not an ICMP echo request".
What's a real ping, if not an ICMP echo request? That's pretty much the
definitive packet for internetwork groping as far as i know. I think that
the more generic sense of ping is a later meaning (BICouldVeryWellBW).
My central server, and this is important, should have a short timeout.
If one client does not respond because it's offline, after max. 10
seconds the central server should continue with the next client.
I'd write a single function that pings a client and waits for a
response/timeout. It then should return True if the client is online,
and False if it is offline. You can then use a list of clients and the
filter() function, to retrieve a list of online clients.
That sounds like a good plan.
To do the timeouts, you want the settimeout method on socket:
import socket
def default_validate(sock):
return True
def ping(host, port, timeout=10.0, validate=default_validate):
"""Ping a specified host on the specified port. The timeout (in
seconds) and a validation function can be set; the validation
function should accept a freshly opened socket and return True if
it's okay, and False if not. This functions returns True if the
specified target can be connected to and yields a valid socket, and
False otherwise.
"""
sock = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
sock.settimeout(timeout)
try:
sock.connect((host, port))
except socket.error:
return False
ok = validate(sock)
sock.close()
return ok
A potential problem with this is that in the worst case, you'll be
spending a little over ten seconds on each socket; if you have a lot of
sockets, that might mean you're not getting through them fast enough.
There are two ways round this: handle several pings in parallel using
threads, or use non-blocking sockets to handle several at once with a
single thread.
tom
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