← Back to branch summary

~ubuntu-branches/ubuntu/precise/linux-lowlatency/precise

« back to all changes in this revision

Viewing changes to lib/dec_and_lock.c

  • Committer: Package Import Robot
  • Author(s): Alessio Igor Bogani
  • Date: 2011-10-26 11:13:05 UTC
  • Revision ID: package-import@ubuntu.com-20111026111305-tz023xykf0i6eosh
Tags: upstream-3.2.0
Import upstream version 3.2.0

Show diffs side-by-side

added added

removed removed

Lines of Context:
lib/dec_and_lock.c
 
1
#include <linux/module.h>
 
2
#include <linux/spinlock.h>
 
3
#include <linux/atomic.h>
 
4
 
 
5
/*
 
6
 * This is an implementation of the notion of "decrement a
 
7
 * reference count, and return locked if it decremented to zero".
 
8
 *
 
9
 * NOTE NOTE NOTE! This is _not_ equivalent to
 
10
 *
 
11
 *      if (atomic_dec_and_test(&atomic)) {
 
12
 *              spin_lock(&lock);
 
13
 *              return 1;
 
14
 *      }
 
15
 *      return 0;
 
16
 *
 
17
 * because the spin-lock and the decrement must be
 
18
 * "atomic".
 
19
 */
 
20
int _atomic_dec_and_lock(atomic_t *atomic, spinlock_t *lock)
 
21
{
 
22
        /* Subtract 1 from counter unless that drops it to 0 (ie. it was 1) */
 
23
        if (atomic_add_unless(atomic, -1, 1))
 
24
                return 0;
 
25
 
 
26
        /* Otherwise do it the slow way */
 
27
        spin_lock(lock);
 
28
        if (atomic_dec_and_test(atomic))
 
29
                return 1;
 
30
        spin_unlock(lock);
 
31
        return 0;
 
32
}
 
33
 
 
34
EXPORT_SYMBOL(_atomic_dec_and_lock);