lib/dec_and_lock.c

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