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spin.h
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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) 1996-2025, 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 */
s_lock.h