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.

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.

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

What if you return False also in writable method?

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.

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.

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.