src/include/storage/shmem.h

   1 /*-------------------------------------------------------------------------
   2  *
   3  * shmem.h
   4  *        shared memory management structures
   5  *
   6  * Historical note:
   7  * A long time ago, Postgres' shared memory region was allowed to be mapped
   8  * at a different address in each process, and shared memory "pointers" were
   9  * passed around as offsets relative to the start of the shared memory region.
  10  * That is no longer the case: each process must map the shared memory region
  11  * at the same address.  This means shared memory pointers can be passed
  12  * around directly between different processes.
  13  *
  14  * Portions Copyright (c) 1996-2021, PostgreSQL Global Development Group
  15  * Portions Copyright (c) 1994, Regents of the University of California
  16  *
  17  * src/include/storage/shmem.h
  18  *
  19  *-------------------------------------------------------------------------
  20  */
  21 #ifndef SHMEM_H
  22 #define SHMEM_H
  23
  24 #include "utils/hsearch.h"
  25
  26
  27 /* shmqueue.c */
  28 typedef struct SHM_QUEUE
  29 {
  30         struct SHM_QUEUE *prev;
  31         struct SHM_QUEUE *next;
  32 } SHM_QUEUE;
  33
  34 /* shmem.c */
  35 extern void InitShmemAccess(void *seghdr);
  36 extern void InitShmemAllocation(void);
  37 extern void *ShmemAlloc(Size size);
  38 extern void *ShmemAllocNoError(Size size);
  39 extern void *ShmemAllocUnlocked(Size size);
  40 extern bool ShmemAddrIsValid(const void *addr);
  41 extern void InitShmemIndex(void);
  42 extern HTAB *ShmemInitHash(const char *name, long init_size, long max_size,
  43                                                    HASHCTL *infoP, int hash_flags);
  44 extern void *ShmemInitStruct(const char *name, Size size, bool *foundPtr);
  45 extern Size add_size(Size s1, Size s2);
  46 extern Size mul_size(Size s1, Size s2);
  47
  48 /* ipci.c */
  49 extern void RequestAddinShmemSpace(Size size);
  50
  51 /* size constants for the shmem index table */
  52  /* max size of data structure string name */
  53 #define SHMEM_INDEX_KEYSIZE              (48)
  54  /* estimated size of the shmem index table (not a hard limit) */
  55 #define SHMEM_INDEX_SIZE                 (64)
  56
  57 /* this is a hash bucket in the shmem index table */
  58 typedef struct
  59 {
  60         char            key[SHMEM_INDEX_KEYSIZE];       /* string name */
  61         void       *location;           /* location in shared mem */
  62         Size            size;                   /* # bytes requested for the structure */
  63         Size            allocated_size; /* # bytes actually allocated */
  64 } ShmemIndexEnt;
  65
  66 /*
  67  * prototypes for functions in shmqueue.c
  68  */
  69 extern void SHMQueueInit(SHM_QUEUE *queue);
  70 extern void SHMQueueElemInit(SHM_QUEUE *queue);
  71 extern void SHMQueueDelete(SHM_QUEUE *queue);
  72 extern void SHMQueueInsertBefore(SHM_QUEUE *queue, SHM_QUEUE *elem);
  73 extern void SHMQueueInsertAfter(SHM_QUEUE *queue, SHM_QUEUE *elem);
  74 extern Pointer SHMQueueNext(const SHM_QUEUE *queue, const SHM_QUEUE *curElem,
  75                                                         Size linkOffset);
  76 extern Pointer SHMQueuePrev(const SHM_QUEUE *queue, const SHM_QUEUE *curElem,
  77                                                         Size linkOffset);
  78 extern bool SHMQueueEmpty(const SHM_QUEUE *queue);
  79 extern bool SHMQueueIsDetached(const SHM_QUEUE *queue);
  80
  81 #endif                                                  /* SHMEM_H */