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db_include/storage/spin.h

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+/*-------------------------------------------------------------------------
+ *
+ * spin.h
+ *	   Hardware-independent implementation of spinlocks.
+ *
+ *
+ *	The hardware-independent interface to spinlocks is defined by the
+ *	typedef "slock_t" and these macros:
+ *
+ *	void SpinLockInit(volatile slock_t *lock)
+ *		Initialize a spinlock (to the unlocked state).
+ *
+ *	void SpinLockAcquire(volatile slock_t *lock)
+ *		Acquire a spinlock, waiting if necessary.
+ *		Time out and abort() if unable to acquire the lock in a
+ *		"reasonable" amount of time --- typically ~ 1 minute.
+ *
+ *	void SpinLockRelease(volatile slock_t *lock)
+ *		Unlock a previously acquired lock.
+ *
+ *	bool SpinLockFree(slock_t *lock)
+ *		Tests if the lock is free. Returns true if free, false if locked.
+ *		This does *not* change the state of the lock.
+ *
+ *	Callers must beware that the macro argument may be evaluated multiple
+ *	times!
+ *
+ *	Load and store operations in calling code are guaranteed not to be
+ *	reordered with respect to these operations, because they include a
+ *	compiler barrier.  (Before PostgreSQL 9.5, callers needed to use a
+ *	volatile qualifier to access data protected by spinlocks.)
+ *
+ *	Keep in mind the coding rule that spinlocks must not be held for more
+ *	than a few instructions.  In particular, we assume it is not possible
+ *	for a CHECK_FOR_INTERRUPTS() to occur while holding a spinlock, and so
+ *	it is not necessary to do HOLD/RESUME_INTERRUPTS() in these macros.
+ *
+ *	These macros are implemented in terms of hardware-dependent macros
+ *	supplied by s_lock.h.  There is not currently any extra functionality
+ *	added by this header, but there has been in the past and may someday
+ *	be again.
+ *
+ *
+ * Portions Copyright (c) 1996-2021, PostgreSQL Global Development Group
+ * Portions Copyright (c) 1994, Regents of the University of California
+ *
+ * src/include/storage/spin.h
+ *
+ *-------------------------------------------------------------------------
+ */
+#ifndef SPIN_H
+#define SPIN_H
+
+#include "storage/s_lock.h"
+#ifndef HAVE_SPINLOCKS
+#include "storage/pg_sema.h"
+#endif
+
+
+#define SpinLockInit(lock)	S_INIT_LOCK(lock)
+
+#define SpinLockAcquire(lock) S_LOCK(lock)
+
+#define SpinLockRelease(lock) S_UNLOCK(lock)
+
+#define SpinLockFree(lock)	S_LOCK_FREE(lock)
+
+
+extern int	SpinlockSemas(void);
+extern Size SpinlockSemaSize(void);
+
+#ifndef HAVE_SPINLOCKS
+extern void SpinlockSemaInit(void);
+extern PGSemaphore *SpinlockSemaArray;
+#endif
+
+#endif							/* SPIN_H */