src/include/storage/spin.h

   1 /*-------------------------------------------------------------------------
   2  *
   3  * spin.h
   4  *         API for spinlocks.
   5  *
   6  *
   7  *      The interface to spinlocks is defined by the typedef "slock_t" and
   8  *      these macros:
   9  *
  10  *      void SpinLockInit(volatile slock_t *lock)
  11  *              Initialize a spinlock (to the unlocked state).
  12  *
  13  *      void SpinLockAcquire(volatile slock_t *lock)
  14  *              Acquire a spinlock, waiting if necessary.
  15  *              Time out and abort() if unable to acquire the lock in a
  16  *              "reasonable" amount of time --- typically ~ 1 minute.
  17  *
  18  *      void SpinLockRelease(volatile slock_t *lock)
  19  *              Unlock a previously acquired lock.
  20  *
  21  *      bool SpinLockFree(slock_t *lock)
  22  *              Tests if the lock is free. Returns true if free, false if locked.
  23  *              This does *not* change the state of the lock.
  24  *
  25  *      Callers must beware that the macro argument may be evaluated multiple
  26  *      times!
  27  *
  28  *      Load and store operations in calling code are guaranteed not to be
  29  *      reordered with respect to these operations, because they include a
  30  *      compiler barrier.  (Before PostgreSQL 9.5, callers needed to use a
  31  *      volatile qualifier to access data protected by spinlocks.)
  32  *
  33  *      Keep in mind the coding rule that spinlocks must not be held for more
  34  *      than a few instructions.  In particular, we assume it is not possible
  35  *      for a CHECK_FOR_INTERRUPTS() to occur while holding a spinlock, and so
  36  *      it is not necessary to do HOLD/RESUME_INTERRUPTS() in these macros.
  37  *
  38  *      These macros are implemented in terms of hardware-dependent macros
  39  *      supplied by s_lock.h.  There is not currently any extra functionality
  40  *      added by this header, but there has been in the past and may someday
  41  *      be again.
  42  *
  43  *
  44  * Portions Copyright (c) 1996-2024, PostgreSQL Global Development Group
  45  * Portions Copyright (c) 1994, Regents of the University of California
  46  *
  47  * src/include/storage/spin.h
  48  *
  49  *-------------------------------------------------------------------------
  50  */
  51 #ifndef SPIN_H
  52 #define SPIN_H
  53
  54 #include "storage/s_lock.h"
  55
  56
  57 #define SpinLockInit(lock)      S_INIT_LOCK(lock)
  58
  59 #define SpinLockAcquire(lock) S_LOCK(lock)
  60
  61 #define SpinLockRelease(lock) S_UNLOCK(lock)
  62
  63 #define SpinLockFree(lock)      S_LOCK_FREE(lock)
  64
  65 #endif                                                  /* SPIN_H */