1 /*------------------------------------------------------------------------- 2 * 3 * pg_sema.h 4 * Platform-independent API for semaphores. 5 * 6 * PostgreSQL requires counting semaphores (the kind that keep track of 7 * multiple unlock operations, and will allow an equal number of subsequent 8 * lock operations before blocking). The underlying implementation is 9 * not the same on every platform. This file defines the API that must 10 * be provided by each port. 11 * 12 * 13 * Portions Copyright (c) 1996-2017, PostgreSQL Global Development Group 14 * Portions Copyright (c) 1994, Regents of the University of California 15 * 16 * src/include/storage/pg_sema.h 17 * 18 *------------------------------------------------------------------------- 19 */ 20 #ifndef PG_SEMA_H 21 #define PG_SEMA_H 22 23 /* 24 * struct PGSemaphoreData and pointer type PGSemaphore are the data structure 25 * representing an individual semaphore. The contents of PGSemaphoreData vary 26 * across implementations and must never be touched by platform-independent 27 * code; hence, PGSemaphoreData is declared as an opaque struct here. 28 * 29 * However, Windows is sufficiently unlike our other ports that it doesn't 30 * seem worth insisting on ABI compatibility for Windows too. Hence, on 31 * that platform just define PGSemaphore as HANDLE. 32 */ 33 #ifndef USE_WIN32_SEMAPHORES 34 typedef struct PGSemaphoreData *PGSemaphore; 35 #else 36 typedef HANDLE PGSemaphore; 37 #endif 38 39 40 /* Report amount of shared memory needed */ 41 extern Size PGSemaphoreShmemSize(int maxSemas); 42 43 /* Module initialization (called during postmaster start or shmem reinit) */ 44 extern void PGReserveSemaphores(int maxSemas, int port); 45 46 /* Allocate a PGSemaphore structure with initial count 1 */ 47 extern PGSemaphore PGSemaphoreCreate(void); 48 49 /* Reset a previously-initialized PGSemaphore to have count 0 */ 50 extern void PGSemaphoreReset(PGSemaphore sema); 51 52 /* Lock a semaphore (decrement count), blocking if count would be < 0 */ 53 extern void PGSemaphoreLock(PGSemaphore sema); 54 55 /* Unlock a semaphore (increment count) */ 56 extern void PGSemaphoreUnlock(PGSemaphore sema); 57 58 /* Lock a semaphore only if able to do so without blocking */ 59 extern bool PGSemaphoreTryLock(PGSemaphore sema); 60 61 #endif /* PG_SEMA_H */ 62