File change notification

Question

Is there any way to obtain a notification in form of a signal or callback invokation, when the selected file is being modified?
More precisely, I need a mechamism to implement a "tail -f" monitoring solution without the use of reads on timeouts.
Sleeping even for a sec is not appropriate for a near real-time monitoring system. Therefore, I need a more robust approach.
I've not found anything that may provide a means to such a trick so far. Moreover, what is frustrating is that tail command is implemented with the use of a sleep-read sequence.
Sincerely
Vladimir

Answer 1

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Is there any way to obtain a notification in form of a
signal or callback invokation, when the selected file
is being modified?
More precisely, I need a mechamism to implement a
"tail -f" monitoring solution without the use of reads
on timeouts.     If you are truely just interested in seeing
if the file changes use stat(2) and get the file size.
     If you truly want to read the file as it
is being writen to, you can open it, seek to somewhere
near the end and do reads. You are not using the
shell as you would with tail -f, you are just a
separate process reading a file that is being appended
to by another process. I assume that the file being
created is opened for sequential access and the writer
is appending to its end. The other process wants
to read from somwhere else in the file, prehaps at
a leisurely pace.
Sleeping even for a sec is not appropriate for a near
real-time monitoring system. Therefore, I need a more
robust approach.
I've not found anything that may provide a means to
such a trick so far. Moreover, what is frustrating is
that tail command is implemented with the use of a
sleep-read sequence.
Sincerely
Vladimir