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Re: signaling when a file is closed



Andrew B. Young wrote:
> I need to know when a process as finished writing
> a file and has closed it.  My only clue is fuser,
> which somehow knows what processes have files open.
> 
> Is there a way for me to set a signal on a file's
> state that lets me know when it has been closed?
> 
> 
> Some background--
> 
> I have a MRI machine that runs GE's canned software
> which writes out one new file of image data per second
> in a known directory.  I need to stream this data
> into another process in near-real-time.
> 
> Using [id]notify I can watch the directory and know
> when a new file is created. But I need to know when
> the file has been closed by the writing process such
> that there is no more data to be read.

Use /proc.

You need to know the process ID of the MRI software: ps -ef | grep might
do this for you.

Take an example: I'm writing this in vim. Vim is using
/tmp/.mutt-kendrick-3668-39.swp as a temporary file.

$ ps -ef | grep vim
james     3704  3668  0 18:00 pts/1    00:00:00 vim +/^$ /tmp/mutt-kendrick-3668-39
james     3711  3428  0 18:00 pts/2    00:00:00 grep vim

$ cd /proc/3704/fd
$ ls -l
total 4
lrwx------  1 james james 64 Feb 22 18:00 0 -> /dev/pts/1
lrwx------  1 james james 64 Feb 22 18:00 1 -> /dev/pts/1
lrwx------  1 james james 64 Feb 22 18:00 2 -> /dev/pts/1
lrwx------  1 james james 64 Feb 22 18:00 4 -> /tmp/.mutt-kendrick-3668-39.swp

When vim closes the file, fd 4 will go away.

Hope this helps,

James.

-- 
E-mail address: james | "The letters are Elvish, of an ancient mode, but the
@westexe.demon.co.uk  | language is that of Microsoft, which I will not utter
                      | here. But this in the Common Tongue is what is said:
                      | By this or any other name, You are well and truly..."


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