LXR linux/include/linux/osq

   1#ifndef __LINUX_OSQ_LOCK_H
   2#define __LINUX_OSQ_LOCK_H
   3
   4/*
   5 * An MCS like lock especially tailored for optimistic spinning for sleeping
   6 * lock implementations (mutex, rwsem, etc).
   7 */
   8struct optimistic_spin_node {
   9        struct optimistic_spin_node *next, *prev;
  10        int locked; /* 1 if lock acquired */
  11        int cpu; /* encoded CPU # + 1 value */
  12};
  13
  14struct optimistic_spin_queue {
  15        /*
  16         * Stores an encoded value of the CPU # of the tail node in the queue.
  17         * If the queue is empty, then it's set to OSQ_UNLOCKED_VAL.
  18         */
  19        atomic_t tail;
  20};
  21
  22#define OSQ_UNLOCKED_VAL (0)
  23
  24/* Init macro and function. */
  25#define OSQ_LOCK_UNLOCKED { ATOMIC_INIT(OSQ_UNLOCKED_VAL) }
  26
  27static inline void osq_lock_init(struct optimistic_spin_queue *lock)
  28{
  29        atomic_set(&lock->tail, OSQ_UNLOCKED_VAL);
  30}
  31
  32extern bool osq_lock(struct optimistic_spin_queue *lock);
  33extern void osq_unlock(struct optimistic_spin_queue *lock);
  34
  35static inline bool osq_is_locked(struct optimistic_spin_queue *lock)
  36{
  37        return atomic_read(&lock->tail) != OSQ_UNLOCKED_VAL;
  38}
  39
  40#endif
  41