Check whether file is being written to

[loial]

How can I check whether a file is being written to by another process
before I access it?

Platform is unix.

 

[Seebs]

How can I check whether a file is being written to by another process
before I access it?

You mean "written to" or "open for possible writing"?

It may be possible (with sufficient privileges) to determine that a
file has been opened for writing. I don't think you can detect
being-written-to.

More importantly, though, the question is irrelevant, because even if
you absolutely, conclusively, prove that a file is not open nor being
written to, before your next machine instruction loads, the file could
be opened and rewritten multiple times by whole new processes that weren't
even running when you checked.

I suggest you look into advisory locks.

-s

 

[Thomas Jollans]

How can I check whether a file is being written to by another process
before I access it?

Platform is unix.

As such, you can't. But you can lock the file using the functions in the fcntl
module.

 

[Diez B. Roggisch]

As such, you can't. But you can lock the file using the functions in the fcntl
module.

Last time I checked, file-locking in unix was co-operative.

Diez

 

[Nobody]

Last time I checked, file-locking in unix was co-operative.

Linux supports mandatory locking, but it's seldom enabled.