Curt Sampson <[EMAIL PROTECTED]> wrote:
> At any rate, it seems to me highly unlikely that, since the child has
> the *same* descriptor as the parent had, that the lock would
> disappear.
It depends on the lock function. After fork():
o with flock() the lock continues to be held, but will be unlocked
if any child process explicitly unlocks it
o with fcntl() the lock is not inherited in the child
o with lockf() the standards and manual pages don't say
Boring reference material follows.
flock
=====
>From the NetBSD manual page:
NOTES
Locks are on files, not file descriptors. That is, file descriptors du-
plicated through dup(2) or fork(2) do not result in multiple instances of
a lock, but rather multiple references to a single lock. If a process
holding a lock on a file forks and the child explicitly unlocks the file,
the parent will lose its lock.
The Red Hat Linux 8.0 manual page has similar wording. (No standards
to check here -- flock() is not standardised in POSIX, X/Open, Single
Unix Standard, ...)
fcntl
=====
The NetBSD manual page notes that these locks are not inherited by
child processes:
Another minor semantic problem with this interface is that locks
are not inherited by a child process created using the fork(2)
function.
Ditto the Single Unix Standard versions 2 and 3.
lockf()
=======
The standards and manual pages that I've checked don't discuss
fork() in relation to lockf(), which seems a peculiar ommission
and makes me suspect that behaviour has varied historically.
In practice I would expect lockf() semantics to be the same as
fcntl().
Regards,
Giles
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