src/include/storage/pg_sema.h

/*-------------------------------------------------------------------------
 *
 * pg_sema.h
 *	  Platform-independent API for semaphores.
 *
 * PostgreSQL requires counting semaphores (the kind that keep track of
 * multiple unlock operations, and will allow an equal number of subsequent
 * lock operations before blocking).  The underlying implementation is
 * not the same on every platform.	This file defines the API that must
 * be provided by each port.
 *
 *
 * Portions Copyright (c) 1996-2009, PostgreSQL Global Development Group
 * Portions Copyright (c) 1994, Regents of the University of California
 *
 * $PostgreSQL: pgsql/src/include/storage/pg_sema.h,v 1.10 2006/10/04 00:30:10 momjian Exp $
 *
 *-------------------------------------------------------------------------
 */
#ifndef PG_SEMA_H
#define PG_SEMA_H

/*
 * PGSemaphoreData and pointer type PGSemaphore are the data structure
 * representing an individual semaphore.  The contents of PGSemaphoreData
 * vary across implementations and must never be touched by platform-
 * independent code.  PGSemaphoreData structures are always allocated
 * in shared memory (to support implementations where the data changes during
 * lock/unlock).
 *
 * pg_config.h must define exactly one of the USE_xxx_SEMAPHORES symbols.
 */

#ifdef USE_NAMED_POSIX_SEMAPHORES

#include <semaphore.h>

typedef sem_t *PGSemaphoreData;
#endif

#ifdef USE_UNNAMED_POSIX_SEMAPHORES

#include <semaphore.h>

typedef sem_t PGSemaphoreData;
#endif

#ifdef USE_SYSV_SEMAPHORES

typedef struct PGSemaphoreData
{
	int			semId;			/* semaphore set identifier */
	int			semNum;			/* semaphore number within set */
} PGSemaphoreData;
#endif

#ifdef USE_WIN32_SEMAPHORES

typedef HANDLE PGSemaphoreData;
#endif

typedef PGSemaphoreData *PGSemaphore;


/* Module initialization (called during postmaster start or shmem reinit) */
extern void PGReserveSemaphores(int maxSemas, int port);

/* Initialize a PGSemaphore structure to represent a sema with count */
extern void PGSemaphoreCreateInitVal(PGSemaphore sema, int initval);
/* Initialize a PGSemaphore structure to represent a sema with count 1 */
static inline void PGSemaphoreCreate(PGSemaphore sema)
{
	PGSemaphoreCreateInitVal(sema, 1);
}

/* Reset a previously-initialized PGSemaphore to have count 0 */
extern void PGSemaphoreReset(PGSemaphore sema);

/* Lock a semaphore (decrement count), blocking if count would be < 0 */
extern void PGSemaphoreLock(PGSemaphore sema, bool interruptOK);

/*
 * Lock a semaphore (decrement count), blocking if count would be < 0.
 * Return true if the lock obtained or false if an interrupt occurred.
 */
extern bool PGSemaphoreLockInterruptable(PGSemaphore sema);

/* Unlock a semaphore (increment count) */
extern void PGSemaphoreUnlock(PGSemaphore sema);

/* Lock a semaphore only if able to do so without blocking */
extern bool PGSemaphoreTryLock(PGSemaphore sema);

#endif   /* PG_SEMA_H */