[Gllug] A programming question. long.

[home at alexhudson.com]

On Thu, Jul 05, 2001 at 04:59:23AM -0700, David Irvine wrote:
> so we need some sort of locking. Enter the spin lock.

Didn't look like a spinlock to me :) A spinlock is:

while ((stat_lock=lock())&&(time<timeout)) if (stat_lock) break;
if (stat_lock) {
	// locked
} else {
	// couldn't attain lock
}

Not recommended for any code anywhere except certain parts of the kernel.
You want a semaphore, courtesy of Djikstra. Certainly not a spinlock, and
certainly not in Perl. You could also use a filelock instead - designate a
file, and flock() it. Just make sure you know the difference between
advisory and mandatory locking.

> Now, heres the tricky bit we only want to lock the
> table, and we only really want it for select
> statements.

Why not use an SQL lock? Are you using a proper database? If so, it may also
have transactions, which are also useful. Even MySQL supports table locking.
Postgres will allow you to lock rows (IIRC - certainly, commercial dbs do),
which might be even more to your liking.

Cheers,

Alex.

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