Design idea for Ping Application

[Andrew Dalke]

Marc:
> I've been searching old posts for ideas, and can't quite come up with
> anything. In short I need an application that will continuously ping
> 11 different hosts and track the status of the pings.

That was a flashback.  I posted a "sndping" module on this
list many years ago.  It made a ping sound for every ping.

> This works, but presents me with a problem. In order to continuously
> ping using the "-t" option for ping, I am unable to perform a
> readlines() command because it hangs. I've tried other variations of
> read commands, but they all hang my system. I guess it keeps looking
> for EOF and never finds it because the thing is still running. Is
> there a type of read command that just takes what is currently in the
> buffer and stores it?

The normal way is to use the select module, at least for unixy
systems.

%cat t.py
import os, select

class Ping:
  def __init__(self, hostname):
    self.hostname = hostname
    timeout = len(hostname) % 5 + 3  # for some variation
    self.infile = os.popen("ping -i %d %s" % (timeout, hostname))
  def fileno(self):
    return self.infile.fileno()
  def readline(self):
    return self.infile.readline()

def report(hostnames):
  pings = [Ping(name) for name in hostnames]
  while 1:
    print "Waiting for another ping ...."
    r, w, e = select.select(pings, [], [], 1)
    for p in r:
      print "Ping", p.hostname, p.readline()[:-1]

if __name__ == "__main__":
  import sys
  if len(sys.argv) == 1:
    raise SystemExit("missing list of machines to ping")
  else:
    report(sys.argv[1:])

%python t.py biopython.org dalkescientific.com python.org
Waiting for another ping ....
Ping dalkescientific.com PING dalkescientific.com (66.39.47.217): 56 data
bytes
Waiting for another ping ....
Ping biopython.org PING biopython.org (155.94.54.81): 56 data bytes
Waiting for another ping ....
Ping python.org PING python.org (194.109.137.226): 56 data bytes
Waiting for another ping ....
Waiting for another ping ....
Waiting for another ping ....
Ping python.org 64 bytes from 194.109.137.226: icmp_seq=0 ttl=238
time=96.553 ms
Waiting for another ping ....
Ping python.org 64 bytes from 194.109.137.226: icmp_seq=1 ttl=238
time=94.554 ms
Waiting for another ping ....
Waiting for another ping ....
Waiting for another ping ....
Ping biopython.org 64 bytes from 155.94.54.81: icmp_seq=0 ttl=55 time=17.084
ms

You could also spawn off a thread for each one, but the select
approach is pretty simple.  (See Aahz's thread tutorial for an example
of how to use threads for a similar task.)

                    Andrew
                    dalke at dalkescientific.com