src/include/storage/pg_shmem.h

   1 /*-------------------------------------------------------------------------
   2  *
   3  * pg_shmem.h
   4  *        Platform-independent API for shared memory support.
   5  *
   6  * Every port is expected to support shared memory with approximately
   7  * SysV-ish semantics; in particular, a memory block is not anonymous
   8  * but has an ID, and we must be able to tell whether there are any
   9  * remaining processes attached to a block of a specified ID.
  10  *
  11  * To simplify life for the SysV implementation, the ID is assumed to
  12  * consist of two unsigned long values (these are key and ID in SysV
  13  * terms).      Other platforms may ignore the second value if they need
  14  * only one ID number.
  15  *
  16  *
  17  * Portions Copyright (c) 1996-2008, PostgreSQL Global Development Group
  18  * Portions Copyright (c) 1994, Regents of the University of California
  19  *
  20  * $PostgreSQL$
  21  *
  22  *-------------------------------------------------------------------------
  23  */
  24 #ifndef PG_SHMEM_H
  25 #define PG_SHMEM_H
  26
  27 typedef struct PGShmemHeader    /* standard header for all Postgres shmem */
  28 {
  29         int32           magic;                  /* magic # to identify Postgres segments */
  30 #define PGShmemMagic  679834894
  31         pid_t           creatorPID;             /* PID of creating process */
  32         Size            totalsize;              /* total size of segment */
  33         Size            freeoffset;             /* offset to first free space */
  34         void       *index;                      /* pointer to ShmemIndex table */
  35 #ifndef WIN32                                   /* Windows doesn't have useful inode#s */
  36         dev_t           device;                 /* device data directory is on */
  37         ino_t           inode;                  /* inode number of data directory */
  38 #endif
  39 } PGShmemHeader;
  40
  41
  42 #ifdef EXEC_BACKEND
  43 extern unsigned long UsedShmemSegID;
  44 extern void *UsedShmemSegAddr;
  45
  46 extern void PGSharedMemoryReAttach(void);
  47 #endif
  48
  49 extern PGShmemHeader *PGSharedMemoryCreate(Size size, bool makePrivate,
  50                                          int port);
  51 extern bool PGSharedMemoryIsInUse(unsigned long id1, unsigned long id2);
  52 extern void PGSharedMemoryDetach(void);
  53
  54 #endif   /* PG_SHMEM_H */