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/*-------------------------------------------------------------------------
*
* shm_toc.h
* shared memory segment table of contents
*
* This is intended to provide a simple way to divide a chunk of shared
* memory (probably dynamic shared memory allocated via dsm_create) into
* a number of regions and keep track of the addresses of those regions or
* key data structures within those regions. This is not intended to
* scale to a large number of keys and will perform poorly if used that
* way; if you need a large number of pointers, store them within some
* other data structure within the segment and only put the pointer to
* the data structure itself in the table of contents.
*
* Portions Copyright (c) 1996-2021, PostgreSQL Global Development Group
* Portions Copyright (c) 1994, Regents of the University of California
*
* src/include/storage/shm_toc.h
*
*-------------------------------------------------------------------------
*/
#ifndef SHM_TOC_H
#define SHM_TOC_H
#include "storage/shmem.h" /* for add_size() */
/* shm_toc is an opaque type known only within shm_toc.c */
typedef struct shm_toc shm_toc;
extern shm_toc *shm_toc_create(uint64 magic, void *address, Size nbytes);
extern shm_toc *shm_toc_attach(uint64 magic, void *address);
extern void *shm_toc_allocate(shm_toc *toc, Size nbytes);
extern Size shm_toc_freespace(shm_toc *toc);
extern void shm_toc_insert(shm_toc *toc, uint64 key, void *address);
extern void *shm_toc_lookup(shm_toc *toc, uint64 key, bool noError);
/*
* Tools for estimating how large a chunk of shared memory will be needed
* to store a TOC and its dependent objects. Note: we don't really support
* large numbers of keys, but it's convenient to declare number_of_keys
* as a Size anyway.
*/
typedef struct
{
Size space_for_chunks;
Size number_of_keys;
} shm_toc_estimator;
#define shm_toc_initialize_estimator(e) \
((e)->space_for_chunks = 0, (e)->number_of_keys = 0)
#define shm_toc_estimate_chunk(e, sz) \
((e)->space_for_chunks = add_size((e)->space_for_chunks, BUFFERALIGN(sz)))
#define shm_toc_estimate_keys(e, cnt) \
((e)->number_of_keys = add_size((e)->number_of_keys, cnt))
extern Size shm_toc_estimate(shm_toc_estimator *e);
#endif /* SHM_TOC_H */
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