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/*-------------------------------------------------------------------------
*
* 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;
struct PGShmemHeader; /* avoid including storage/pg_shmem.h here */
extern void InitShmemAccess(struct PGShmemHeader *seghdr);
extern void InitShmemAllocation(void);
extern void *ShmemAlloc(Size size);
extern void *ShmemAllocNoError(Size size);
extern void *ShmemAllocUnlocked(Size size);
extern bool ShmemAddrIsValid(const void *addr);
extern void InitShmemIndex(void);
extern HTAB *ShmemInitHash(const char *name, long init_size, long 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 */
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