[Zope] Re: Running more than one instance on windows often block each other

29 Jul 2005

      The attached hasn't failed on my box (Win XP Pro SP2, Python 2.3.5)
for about two hours, running it in 3 processes.  Was using 2 processes
before; discovered it was much easier to provoke problems using 3; but
the # of ephemeral ports in use increases too, typically hovering
between 7-8 thousand after reaching steady state.

I'll let it run the rest of today, and start changing ZODB code if it
still looks good.  I hope someone(s) else will then volunteer to port
the Windows changes to all the copies of Medusa code in the various
active Zope trunks and branches.

This suffers from what I still believe to be bugs in the Windows
socket implementation, but there is only one symptom I see with this,
and the code uses try/except to implement what appears to be a
reliable workaround.

import socket, errno
import time, random

class BindError(Exception):
    pass

def socktest29():
    w = socket.socket()

    # Disable buffering -- pulling the trigger sends 1 byte,
    # and we want that sent immediately, to wake up asyncore's
    # select() ASAP.
    w.setsockopt(socket.IPPROTO_TCP, socket.TCP_NODELAY, 1)

    count = 0
    while 1:
        count += 1
        # Bind to a local port; for efficiency, let the OS pick
        # a free port for us.
        # Unfortunately, stress tests showed that we may not
        # be able to connect to that port ("Address already in
        # use") despite that the OS picked it.  This appears
        # to be a race bug in the Windows socket implementation.
        # So we loop until a connect() succeeds (almost always
        # on the first try).
        a = socket.socket()
        a.bind(("127.0.0.1", 0))
        print 'b',
        connect_address = a.getsockname()  # assigned (host, port) pair
        a.listen(1)
        try:
            w.connect(connect_address)
            print 'c',
            break
        except socket.error, detail:
            if detail[0] != errno.WSAEADDRINUSE:
                # "Address already in use" is the only error
                # I've seen on two WinXP Pro SP2 boxes, under
                # Pythons 2.3.5 and 2.4.1.
                raise
            # (10048, 'Address already in use')
            # assert count <= 2 # never triggered in Tim's tests
            if count >= 10:  # I've never seen it go above 2
                a.close()
                w.close()
                raise BindError("Cannot bind trigger!")
            # Close `a` and try again.  Note:  I originally put a short
            # sleep() here, but it didn't appear to help or hurt.
            print
            print detail, a.getsockname()
            a.close()

    r, addr = a.accept()  # r becomes asyncore's (self.)socket
    print 'a',
    a.close()
    print 'c',

    return (r, w)

sofar = []
try:
   while 1:
       print '.',
       stuff = socktest29()
       sofar.append(stuff)
       time.sleep(random.random()/10)
       if len(sofar) == 50:
           tup = sofar.pop(0)
           r, w = tup
           msg = str(random.randrange(1000000))
           w.send(msg)
           msg2 = r.recv(100)
           assert msg == msg2, (msg, msg2, r.getsockname(), w.getsockname())
           r.close()
           w.close()
except KeyboardInterrupt:
   for tup in sofar:
       for s in tup:
           s.close()

[Zope] Re: Running more than one instance on windows often block each other

Tim Peters