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) 1996-2024, PostgreSQL Global Development Group
  18  * Portions Copyright (c) 1994, Regents of the University of California
  19  *
  20  * src/include/storage/pg_shmem.h
  21  *
  22  *-------------------------------------------------------------------------
  23  */
  24 #ifndef PG_SHMEM_H
  25 #define PG_SHMEM_H
  26
  27 #include "storage/dsm_impl.h"
  28
  29 typedef struct PGShmemHeader    /* standard header for all Postgres shmem */
  30 {
  31         int32           magic;                  /* magic # to identify Postgres segments */
  32 #define PGShmemMagic  679834894
  33         pid_t           creatorPID;             /* PID of creating process (set but unread) */
  34         Size            totalsize;              /* total size of segment */
  35         Size            freeoffset;             /* offset to first free space */
  36         dsm_handle      dsm_control;    /* ID of dynamic shared memory control seg */
  37         void       *index;                      /* pointer to ShmemIndex table */
  38 #ifndef WIN32                                   /* Windows doesn't have useful inode#s */
  39         dev_t           device;                 /* device data directory is on */
  40         ino_t           inode;                  /* inode number of data directory */
  41 #endif
  42 } PGShmemHeader;
  43
  44 /* GUC variables */
  45 extern PGDLLIMPORT int shared_memory_type;
  46 extern PGDLLIMPORT int huge_pages;
  47 extern PGDLLIMPORT int huge_page_size;
  48
  49 /* Possible values for huge_pages and huge_pages_status */
  50 typedef enum
  51 {
  52         HUGE_PAGES_OFF,
  53         HUGE_PAGES_ON,
  54         HUGE_PAGES_TRY,                         /* only for huge_pages */
  55         HUGE_PAGES_UNKNOWN,                     /* only for huge_pages_status */
  56 }                       HugePagesType;
  57
  58 /* Possible values for shared_memory_type */
  59 typedef enum
  60 {
  61         SHMEM_TYPE_WINDOWS,
  62         SHMEM_TYPE_SYSV,
  63         SHMEM_TYPE_MMAP,
  64 }                       PGShmemType;
  65
  66 #ifndef WIN32
  67 extern PGDLLIMPORT unsigned long UsedShmemSegID;
  68 #else
  69 extern PGDLLIMPORT HANDLE UsedShmemSegID;
  70 extern PGDLLIMPORT void *ShmemProtectiveRegion;
  71 #endif
  72 extern PGDLLIMPORT void *UsedShmemSegAddr;
  73
  74 #if !defined(WIN32) && !defined(EXEC_BACKEND)
  75 #define DEFAULT_SHARED_MEMORY_TYPE SHMEM_TYPE_MMAP
  76 #elif !defined(WIN32)
  77 #define DEFAULT_SHARED_MEMORY_TYPE SHMEM_TYPE_SYSV
  78 #else
  79 #define DEFAULT_SHARED_MEMORY_TYPE SHMEM_TYPE_WINDOWS
  80 #endif
  81
  82 #ifdef EXEC_BACKEND
  83 extern void PGSharedMemoryReAttach(void);
  84 extern void PGSharedMemoryNoReAttach(void);
  85 #endif
  86
  87 extern PGShmemHeader *PGSharedMemoryCreate(Size size,
  88                                                                                    PGShmemHeader **shim);
  89 extern bool PGSharedMemoryIsInUse(unsigned long id1, unsigned long id2);
  90 extern void PGSharedMemoryDetach(void);
  91 extern void GetHugePageSize(Size *hugepagesize, int *mmap_flags);
  92
  93 #endif                                                  /* PG_SHMEM_H */