src/include/storage/pg_sema.h

   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) 1996-2024, 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);
  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 */