how do I listen on a socket without sucking up all the CPU time?

[Joshua Muskovitz]

Hi all,

I've got a worker thread which listens on an ICMP (ping) socket for replies
to pings that I send out (on the same socket from a different thread).  All
of this code runs fine, but the socket is set to be non-blocking, so
recvfrom() returns immediately most of the time, and this thread runs like
mad, consuming all the available CPU time.  It is definitely this thread --
when I don't create this particular thread, CPU usage drops back to normal.

Is there a way to somehow do this with signals of some sort?  This needs to
run on NT/2000 as well as *nix.

Any other suggestions would also be gratefully welcomed...

-- josh

========= cut here for code =========
class PingThread(threading.Thread):
    def __init__(self):
        threading.Thread.__init__(self)
        self.pid = os.getpid()

    def run(self):
        global KEEP_RUNNING

        while KEEP_RUNNING:
            try:
                # attempt to receive a ping
                pkt, who = PingScheme.icmpSocket.recvfrom(512)
                ipPacket = ip.Packet(pkt)
                icmpPacket = icmp.Packet(ipPacket.data)
                now = time.time()
                if icmpPacket.type == icmp.ICMP_ECHOREPLY:
                    if icmpPacket.id == self.pid:
                        # this means the ping is for us
[handler here snipped]
            except socket.error:
                pass
            except ValueError:
                pass
            except KeyboardInterrupt:
                KEEP_RUNNING = 0





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