asyncore does not react properly on close()

[tgeorgiev]

BPO	10878
Nosy	@terryjreedy, @giampaolo

^{Note: these values reflect the state of the issue at the time it was migrated and might not reflect the current state.}

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GitHub fields:

assignee = None
closed_at = <Date 2013-07-31.18:54:34.969>
created_at = <Date 2011-01-10.06:40:22.724>
labels = ['invalid', 'type-bug', 'library']
title = 'asyncore does not react properly on close()'
updated_at = <Date 2013-07-31.18:54:34.957>
user = 'https://bugs.python.org/tgeorgiev'

bugs.python.org fields:

activity = <Date 2013-07-31.18:54:34.957>
actor = 'terry.reedy'
assignee = 'none'
closed = True
closed_date = <Date 2013-07-31.18:54:34.969>
closer = 'terry.reedy'
components = ['Library (Lib)']
creation = <Date 2011-01-10.06:40:22.724>
creator = 'tgeorgiev'
dependencies = []
files = []
hgrepos = []
issue_num = 10878
keywords = []
message_count = 10.0
messages = ['125882', '125883', '125894', '125895', '125897', '127149', '127150', '183760', '183761', '194007']
nosy_count = 4.0
nosy_names = ['terry.reedy', 'giampaolo.rodola', 'tgeorgiev', 'Gavin M. Roy']
pr_nums = []
priority = 'normal'
resolution = 'not a bug'
stage = 'resolved'
status = 'closed'
superseder = None
type = 'behavior'
url = 'https://bugs.python.org/issue10878'
versions = ['Python 2.7']

[tgeorgiev]

I am trying to add a simple timer to each created socket and destroy it
once the timer expires:

class client(asyncore.dispatcher):
    def __init__(self,host):
    ...
    self.timeout = time.time() + 5

    def readable(self):
        if time.time() >= self.timeout:
            self.close()
        return True

When running that code, it raises an exception:

asyncore.loop(timeout=0.8)
  File "/usr/lib/python2.6/asyncore.py", line 211, in loop
    poll_fun(timeout)
  File "/usr/lib/python2.6/asyncore.py", line 144, in poll
    raise
  File "/usr/lib/python2.6/asyncore.py", line 141, in poll
    r, w, e = select.select(r, w, e, timeout)
select.error: (9, 'Bad file descriptor')

Although del_channel is executed properly and the socket is removed from the map, the poll function is not updated with that info and continues to keep the socket into the r,w,e.

[giampaolo]

Problem is you have to return False right after close().
There's an open issue to add a scheduler to asyncore:
http://bugs.python.org/issue1641
Closing this out as invalid.

[tgeorgiev]

Sorry, I forgot to mention - I have already tried to return False, but there was no difference.

def readable(self):
        if time.time() >= self.timeout:
            self.close()
            return False
         else:
            return True

[giampaolo]

What if you return False also in writable method?

[tgeorgiev]

Precisely, I traced down the problem by putting a simple "breakpoint"
in asyncore.py:

def poll(timeout=0.0, map=None):
    if map is None:
        map = socket_map
    if map:
        r = []; w = []; e = []
        for fd, obj in map.items():
            is_r = obj.readable()
            print "Readable??? -->" , is_r
            is_w = obj.writable()
            if is_r:
                r.append(fd)
            if is_w:
                w.append(fd)
            if is_r or is_w:
                e.append(fd)
        if [] == r == w == e:
            time.sleep(timeout)
            return

    print r,w,e

try:
r, w, e = select.select(r, w, e, timeout)
except select.error, err:
if err.args[0] != EINTR:
raise
else:
return

And here it comes:

[5] [5] [5]
Readable??? --> True
[5] [5] [5]
Readable??? --> True
[5] [5] [5]
Readable??? --> False
[] [5] [5]

Traceback (most recent call last):
  File "./dlms_client.py", line 136, in <module>
    asyncore.loop(timeout=0.8)
  File "/usr/lib/python2.6/asyncore.py", line 213, in loop
    poll_fun(timeout)
  File "/usr/lib/python2.6/asyncore.py", line 146, in poll
    raise
  File "/usr/lib/python2.6/asyncore.py", line 143, in poll
    r, w, e = select.select(r, w, e, timeout)
select.error: (9, 'Bad file descriptor')

So, in order this to work, on first sight all r,w,e must not point to
a socket that has been already closed. Now I am going to think for a workaround at least.

[GavinMRoy]

What I noticed in tracing through the code is that it's getting stuck in a loop because it depends on grabbing asyncore.socket_map if map is null when passed into asyncore.loop. I got around this by appending:

asyncore.loop(0.1, map=[], count=1)

After my close(). I believe this bypasses the grab of socket_map from asyncore.socket_map and allows the while loop in asyncore.loop to exit cleanly.

[GavinMRoy]

For more clarity, I am passing in a list because it will evaluate as False in the while loop on 209 and 213. The fix is to add len(map) to the while loops on those lines.

[terryjreedy]

Teodor or Gavin: is the (mis)behavior the same in 3.3?

Giampaolo: has the OP identified a fixable misbehavior relative to the documented behavior, making this a valid behavior issue?
Or is this instead an enhancement request, possibly superseded by bpo-1641?

[giampaolo]

I'm not sure what the OP and Gavin are complaining about in their last messages. Could you guys be more clear and/or provide a code sample which reproduces the problem?

[terryjreedy]

I am re-closing as there is no defined bug to fix, and 2.7 is closed to enhancements.