1 /*-------------------------------------------------------------------------
4 * Hardware-independent implementation of spinlocks.
7 * The hardware-independent interface to spinlocks is defined by the
8 * typedef "slock_t" and these macros:
10 * void SpinLockInit(volatile slock_t *lock)
11 * Initialize a spinlock (to the unlocked state).
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.
18 * void SpinLockRelease(volatile slock_t *lock)
19 * Unlock a previously acquired lock.
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.
25 * Callers must beware that the macro argument may be evaluated multiple
28 * CAUTION: Care must be taken to ensure that loads and stores of
29 * shared memory values are not rearranged around spinlock acquire
30 * and release. This is done using the "volatile" qualifier: the C
31 * standard states that loads and stores of volatile objects cannot
32 * be rearranged *with respect to other volatile objects*. The
33 * spinlock is always written through a volatile pointer by the
34 * spinlock macros, but this is not sufficient by itself: code that
35 * protects shared data with a spinlock MUST reference that shared
36 * data through a volatile pointer.
38 * Keep in mind the coding rule that spinlocks must not be held for more
39 * than a few instructions. In particular, we assume it is not possible
40 * for a CHECK_FOR_INTERRUPTS() to occur while holding a spinlock, and so
41 * it is not necessary to do HOLD/RESUME_INTERRUPTS() in these macros.
43 * These macros are implemented in terms of hardware-dependent macros
44 * supplied by s_lock.h. There is not currently any extra functionality
45 * added by this header, but there has been in the past and may someday
49 * Portions Copyright (c) 1996-2008, PostgreSQL Global Development Group
50 * Portions Copyright (c) 1994, Regents of the University of California
52 * $PostgreSQL: pgsql/src/include/storage/spin.h,v 1.30 2008/01/01 19:45:59 momjian Exp $
54 *-------------------------------------------------------------------------
59 #include "storage/s_lock.h"
62 #define SpinLockInit(lock) S_INIT_LOCK(lock)
64 #define SpinLockAcquire(lock) S_LOCK(lock)
66 #define SpinLockRelease(lock) S_UNLOCK(lock)
68 #define SpinLockFree(lock) S_LOCK_FREE(lock)
71 extern int SpinlockSemas(void);