linux-stable/lib/dec_and_lock.c
Linus Torvalds 1da177e4c3 Linux-2.6.12-rc2
Initial git repository build. I'm not bothering with the full history,
even though we have it. We can create a separate "historical" git
archive of that later if we want to, and in the meantime it's about
3.2GB when imported into git - space that would just make the early
git days unnecessarily complicated, when we don't have a lot of good
infrastructure for it.

Let it rip!
2005-04-16 15:20:36 -07:00

40 lines
963 B
C

#include <linux/module.h>
#include <linux/spinlock.h>
#include <asm/atomic.h>
/*
* This is an architecture-neutral, but slow,
* implementation of the notion of "decrement
* a reference count, and return locked if it
* decremented to zero".
*
* NOTE NOTE NOTE! This is _not_ equivalent to
*
* if (atomic_dec_and_test(&atomic)) {
* spin_lock(&lock);
* return 1;
* }
* return 0;
*
* because the spin-lock and the decrement must be
* "atomic".
*
* This slow version gets the spinlock unconditionally,
* and releases it if it isn't needed. Architectures
* are encouraged to come up with better approaches,
* this is trivially done efficiently using a load-locked
* store-conditional approach, for example.
*/
#ifndef ATOMIC_DEC_AND_LOCK
int _atomic_dec_and_lock(atomic_t *atomic, spinlock_t *lock)
{
spin_lock(lock);
if (atomic_dec_and_test(atomic))
return 1;
spin_unlock(lock);
return 0;
}
EXPORT_SYMBOL(_atomic_dec_and_lock);
#endif