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) 1996-2008, PostgreSQL Global Development Group
  14  * Portions Copyright (c) 1994, Regents of the University of California
  15  *
  16  * $PostgreSQL$
  17  *
  18  *-------------------------------------------------------------------------
  19  */
  20 #ifndef PG_SEMA_H
  21 #define PG_SEMA_H
  22
  23 /*
  24  * PGSemaphoreData and pointer type PGSemaphore are the data structure
  25  * representing an individual semaphore.  The contents of PGSemaphoreData
  26  * vary across implementations and must never be touched by platform-
  27  * independent code.  PGSemaphoreData structures are always allocated
  28  * in shared memory (to support implementations where the data changes during
  29  * lock/unlock).
  30  *
  31  * pg_config.h must define exactly one of the USE_xxx_SEMAPHORES symbols.
  32  */
  33
  34 #ifdef USE_NAMED_POSIX_SEMAPHORES
  35
  36 #include <semaphore.h>
  37
  38 typedef sem_t *PGSemaphoreData;
  39 #endif
  40
  41 #ifdef USE_UNNAMED_POSIX_SEMAPHORES
  42
  43 #include <semaphore.h>
  44
  45 typedef sem_t PGSemaphoreData;
  46 #endif
  47
  48 #ifdef USE_SYSV_SEMAPHORES
  49
  50 typedef struct PGSemaphoreData
  51 {
  52         int                     semId;                  /* semaphore set identifier */
  53         int                     semNum;                 /* semaphore number within set */
  54 } PGSemaphoreData;
  55 #endif
  56
  57 #ifdef USE_WIN32_SEMAPHORES
  58
  59 typedef HANDLE PGSemaphoreData;
  60 #endif
  61
  62 typedef PGSemaphoreData *PGSemaphore;
  63
  64
  65 /* Module initialization (called during postmaster start or shmem reinit) */
  66 extern void PGReserveSemaphores(int maxSemas, int port);
  67
  68 /* Initialize a PGSemaphore structure to represent a sema with count 1 */
  69 extern void PGSemaphoreCreate(PGSemaphore sema);
  70
  71 /* Reset a previously-initialized PGSemaphore to have count 0 */
  72 extern void PGSemaphoreReset(PGSemaphore sema);
  73
  74 /* Lock a semaphore (decrement count), blocking if count would be < 0 */
  75 extern void PGSemaphoreLock(PGSemaphore sema, bool interruptOK);
  76
  77 /* Unlock a semaphore (increment count) */
  78 extern void PGSemaphoreUnlock(PGSemaphore sema);
  79
  80 /* Lock a semaphore only if able to do so without blocking */
  81 extern bool PGSemaphoreTryLock(PGSemaphore sema);
  82
  83 #endif   /* PG_SEMA_H */