[net-next-2.6.git] / lib / dec_and_lock.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.
 */
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);
Commit	Line	Data
1da177e4 LT	1	#include <linux/module.h>
	2	#include <linux/spinlock.h>
	3	#include <asm/atomic.h>
	4
	5	/*
	6	* This is an architecture-neutral, but slow,
	7	* implementation of the notion of "decrement
	8	* a reference count, and return locked if it
	9	* decremented to zero".
	10	*
	11	* NOTE NOTE NOTE! This is _not_ equivalent to
	12	*
	13	* if (atomic_dec_and_test(&atomic)) {
	14	* spin_lock(&lock);
	15	* return 1;
	16	* }
	17	* return 0;
	18	*
	19	* because the spin-lock and the decrement must be
	20	* "atomic".
	21	*
	22	* This slow version gets the spinlock unconditionally,
	23	* and releases it if it isn't needed. Architectures
	24	* are encouraged to come up with better approaches,
	25	* this is trivially done efficiently using a load-locked
	26	* store-conditional approach, for example.
	27	*/
1da177e4 LT	28	int _atomic_dec_and_lock(atomic_t atomic, spinlock_t lock)
	29	{
	30	spin_lock(lock);
	31	if (atomic_dec_and_test(atomic))
	32	return 1;
	33	spin_unlock(lock);
	34	return 0;
	35	}
	36
	37	EXPORT_SYMBOL(_atomic_dec_and_lock);