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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) 1996-2024, 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 */
s_lock.h