On 02:43 am, ivo...@gmail.com wrote:
I'm trying to simply imitate what "tail -f" does, i.e. read a file,
wait
until it's appended to and process the new data, but apparently I'm
missing something.
The code is:
54 f = file(filename, "r", 1)
55 f.seek(-1000, os.SEEK_END)
56 ff = fcntl.fcntl(f.fileno(), fcntl.F_GETFL)
57 fcntl.fcntl(f.fileno(), fcntl.F_SETFL, ff | os.O_NONBLOCK)
58
59 pe = select.poll()
60 pe.register(f)
61 while True:
62 print repr(f.read())
63 print pe.poll(1000)
The problem is: poll() always returns that the fd is ready (without
waiting), but read() always returns an empty string. Actually, it
doesn't matter if I turn O_NDELAY on or off. select() does the same.
Any advice?
select(), poll(), epoll, etc. all have the problem where they don't
support files (in the thing-on-a-filesystem sense) at all. They just
indicate the descriptor is readable or writeable all the time,
regardless.
"tail -f" is implemented by sleeping a little bit and then reading to
see if there's anything new.
Jean-Paul
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