Alan Cox wrote:
>
> > have got it right. Does anyone know what this part of the
> > flock(2) manpage means?
> >
> > A single file may not simultaneously have both shared and
> > exclusive locks.
>
> AFAIK its saying LOCK_EX is exclusive and blocks shared locks and vice
> versa. Its a standard reader-writer lock setup. LOCK_EX is writer, LOCK_SH
> is reader.
Thanks, Alan. You're right, and this is indeed how the current
implementation behaves. The DG/UX manpage makes a bit more sense
here.
One interesting factoid: if a process currently has an exclusive
lock, and it changes that to an exclusive lock (ie: no change),
this has the effect of dropping the lock and reclaiming it.
The DG/UX dg_flock() departs from BSD in that "Upgrading a lock
will be an atomic operation. That is, a lock is not released
to upgrade that lock". Linux doesn't do that - the lock is
effectively dropped and reclaimed when we go from LOCK_SH to LOCK_EX.
Even the DG/UX manpage doesn't say what happens when you sidegrade
the lock. LOCK_EX->LOCK_EX :)
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This archive was generated by hypermail 2b29 : Tue Nov 07 2000 - 21:00:16 EST