1 /*-------------------------------------------------------------------------
2  *
3  * spin.h
4  *	   Hardware-independent implementation of spinlocks.
5  *
6  *
7  *	The hardware-independent interface to spinlocks is defined by the
8  *	typedef "slock_t" and 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) 1996-2016, 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 #ifndef HAVE_SPINLOCKS
56 #include "storage/pg_sema.h"
57 #endif
58 
59 
60 #define SpinLockInit(lock)	S_INIT_LOCK(lock)
61 
62 #define SpinLockAcquire(lock) S_LOCK(lock)
63 
64 #define SpinLockRelease(lock) S_UNLOCK(lock)
65 
66 #define SpinLockFree(lock)	S_LOCK_FREE(lock)
67 
68 
69 extern int	SpinlockSemas(void);
70 extern Size SpinlockSemaSize(void);
71 
72 #ifndef HAVE_SPINLOCKS
73 extern void SpinlockSemaInit(PGSemaphore);
74 extern PGSemaphore SpinlockSemaArray;
75 #endif
76 
77 #endif   /* SPIN_H */
78