With use_poll=True on linux, asyncore calls handle_write() after the
socket has been closed.

More specifically, it looks like asyncore dispatches handle_read() and
handle_close() events between the writable() test and the corresponding
handle_write() call. If handle_close() calls close(), as asyncore's
default implementation does, the subsequent handle_write() will fail and
generate an EBADF (bad file descriptor) exception. If handle_error()
also calls close(), as asyncore's default implementation does, this will
mean close() gets called twice on the same socket.

I am attaching example code which demonstrates the problem on Linux
2.6.24 using python 2.5.2, 2.5.3rc1, and 2.6. In one window, run
pollwritefail.py. In another window, establish a TCP connection to port
12345 and immediately close it without reading or writing. This can be
done from within the python interactive interpreter like this:

  import socket
  s=socket.socket( socket.AF_INET, socket.SOCK_STREAM); s.connect(
    ('localhost', 12345)); s.close()

The output from pollwritefail.py will look like this:

writable() - asyncore asked if we have data to write
handle_read() - asyncore asked us to read
handle_close() - asyncore said the remote host closed connection
close() - we are closing our end of the connection
handle_write() - asyncore asked us to write
handle_error() - asyncore exception: (9, 'Bad file descriptor')
close() - we are closing our end of the connection

IMHO, two things need fixing here:

1. When writable() returns True, the next handler asyncore calls should
   be handle_write(). Calling other handlers in between risks invalidating
   the writable() return value.

2. After close(), asyncore should not call handle_write(), even if
   writable() would return true.

This problem must have been solved at some point because this is what I get now on Linux by using python 2.7:

writable() - asyncore asked if we have data to write
handle_read() - asyncore asked us to read
handle_close() - asyncore said the remote host closed connection
close() - we are closing our end of the connection
handle_close() - asyncore said the remote host closed connection
close() - we are closing our end of the connection

Closing out as outdated.