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62 lines
2.1 KiB
C
62 lines
2.1 KiB
C
/*-------------------------------------------------------------------------
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*
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* pg_sema.h
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* Platform-independent API for semaphores.
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*
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* PostgreSQL requires counting semaphores (the kind that keep track of
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* multiple unlock operations, and will allow an equal number of subsequent
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* lock operations before blocking). The underlying implementation is
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* not the same on every platform. This file defines the API that must
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* be provided by each port.
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*
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*
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* Portions Copyright (c) 1996-2023, PostgreSQL Global Development Group
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* Portions Copyright (c) 1994, Regents of the University of California
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*
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* src/include/storage/pg_sema.h
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*
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*-------------------------------------------------------------------------
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*/
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#ifndef PG_SEMA_H
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#define PG_SEMA_H
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/*
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* struct PGSemaphoreData and pointer type PGSemaphore are the data structure
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* representing an individual semaphore. The contents of PGSemaphoreData vary
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* across implementations and must never be touched by platform-independent
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* code; hence, PGSemaphoreData is declared as an opaque struct here.
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*
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* However, Windows is sufficiently unlike our other ports that it doesn't
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* seem worth insisting on ABI compatibility for Windows too. Hence, on
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* that platform just define PGSemaphore as HANDLE.
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*/
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#ifndef USE_WIN32_SEMAPHORES
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typedef struct PGSemaphoreData *PGSemaphore;
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#else
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typedef HANDLE PGSemaphore;
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#endif
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/* Report amount of shared memory needed */
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extern Size PGSemaphoreShmemSize(int maxSemas);
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/* Module initialization (called during postmaster start or shmem reinit) */
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extern void PGReserveSemaphores(int maxSemas);
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/* Allocate a PGSemaphore structure with initial count 1 */
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extern PGSemaphore PGSemaphoreCreate(void);
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/* Reset a previously-initialized PGSemaphore to have count 0 */
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extern void PGSemaphoreReset(PGSemaphore sema);
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/* Lock a semaphore (decrement count), blocking if count would be < 0 */
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extern void PGSemaphoreLock(PGSemaphore sema);
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/* Unlock a semaphore (increment count) */
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extern void PGSemaphoreUnlock(PGSemaphore sema);
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/* Lock a semaphore only if able to do so without blocking */
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extern bool PGSemaphoreTryLock(PGSemaphore sema);
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#endif /* PG_SEMA_H */
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