I thought I would share this nasty little gotcha with the group.
Consider the following code fragment:
<start>
print 'starting kbd thread'
keyboard_thread = thread.start_new_thread(kbd_driver (port_q,kbd_q))
print 'starting main loop'
error = Mainloop(s,port_q,active_q_list)
<end>
It produces, as output, the following:
starting kbd thread
we get here - a
It does not print 'starting main loop', the Mainloop routine
is never executed, and no exceptions are raised.
Here is the offending routine that seems to capture the control:
<start>
def kbd_driver(out_q,in_q):
"""
thread to look for keyboard input and to put it on the queue out_q
also looks for replies on in_q and prints them
"""
kbdname = '/dev/stdin'
kbd = open(kbdname,'r+',1) # Reading, line buffered
unblock(kbd) # Call the magic to unblock keyboard
print 'we get here - a'
while True:
try:
d = kbd.readline() # see if any kbd input
except:
IOError
try:
msg=in_q.get(block=False)
except Queue.Empty:
time.sleep(0.1)
continue
print msg
time.sleep(0.1)
continue
d = d.rstrip() # get rid of line feed
out_q.put([d + '\r',in_q]) # add a carriage return and return q and send
to port
<end>
The unblock is a routine that unblocks a port using fcntl - it
is not the problem. In case you don't believe me, here it is:
def unblock(f):
"""Given file 'f', sets its unblock flag to true."""
fcntl.fcntl(f.fileno(), fcntl.F_SETFL, os.O_NONBLOCK)
I will post the solution tomorrow when I read my mail,
if no one has spotted it by then.
- Hendrik
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