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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) 1996-2020, 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
/*
* struct 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; hence, PGSemaphoreData is declared as an opaque struct here.
*
* However, Windows is sufficiently unlike our other ports that it doesn't
* seem worth insisting on ABI compatibility for Windows too. Hence, on
* that platform just define PGSemaphore as HANDLE.
*/
#ifndef USE_WIN32_SEMAPHORES
typedef struct PGSemaphoreData *PGSemaphore;
#else
typedef HANDLE PGSemaphore;
#endif
/* Report amount of shared memory needed */
extern Size PGSemaphoreShmemSize(int maxSemas);
/* Module initialization (called during postmaster start or shmem reinit) */
extern void PGReserveSemaphores(int maxSemas);
/* Allocate a PGSemaphore structure with initial count 1 */
extern PGSemaphore PGSemaphoreCreate(void);
/* 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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