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/*-------------------------------------------------------------------------
*
* 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) 1996-2016, PostgreSQL Global Development Group
* Portions Copyright (c) 1994, Regents of the University of California
*
* src/include/storage/pg_sema.h
*
*-------------------------------------------------------------------------
*/
#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 1 */
extern void PGSemaphoreCreate(PGSemaphore sema);
/* 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);
/* 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 */
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