shmem.h

Go to the documentation of this file.

/*-------------------------------------------------------------------------
 *
 * shmem.h
 *    shared memory management structures
 *
 * Historical note:
 * A long time ago, Postgres' shared memory region was allowed to be mapped
 * at a different address in each process, and shared memory "pointers" were
 * passed around as offsets relative to the start of the shared memory region.
 * That is no longer the case: each process must map the shared memory region
 * at the same address.  This means shared memory pointers can be passed
 * around directly between different processes.
 *
 * Portions Copyright (c) 1996-2025, PostgreSQL Global Development Group
 * Portions Copyright (c) 1994, Regents of the University of California
 *
 * src/include/storage/shmem.h
 *
 *-------------------------------------------------------------------------
 */
#ifndef SHMEM_H
#define SHMEM_H
 
#include "storage/spin.h"
#include "utils/hsearch.h"
 
 
/* shmem.c */
extern PGDLLIMPORT slock_t *ShmemLock;
typedef struct PGShmemHeader PGShmemHeader; /* avoid including
                                             * storage/pg_shmem.h here */
extern void InitShmemAccess(PGShmemHeader *seghdr);
extern void InitShmemAllocation(void);
extern void *ShmemAlloc(Size size);
extern void *ShmemAllocNoError(Size size);
extern bool ShmemAddrIsValid(const void *addr);
extern void InitShmemIndex(void);
extern HTAB *ShmemInitHash(const char *name, int64 init_size, int64 max_size,
                           HASHCTL *infoP, int hash_flags);
extern void *ShmemInitStruct(const char *name, Size size, bool *foundPtr);
extern Size add_size(Size s1, Size s2);
extern Size mul_size(Size s1, Size s2);
 
extern PGDLLIMPORT Size pg_get_shmem_pagesize(void);
 
/* ipci.c */
extern void RequestAddinShmemSpace(Size size);
 
/* size constants for the shmem index table */
 /* max size of data structure string name */
#define SHMEM_INDEX_KEYSIZE      (48)
 /* estimated size of the shmem index table (not a hard limit) */
#define SHMEM_INDEX_SIZE         (64)
 
/* this is a hash bucket in the shmem index table */
typedef struct
{
    char        key[SHMEM_INDEX_KEYSIZE];   /* string name */
    void       *location;       /* location in shared mem */
    Size        size;           /* # bytes requested for the structure */
    Size        allocated_size; /* # bytes actually allocated */
} ShmemIndexEnt;
 
#endif                          /* SHMEM_H */