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) 1996-2020, 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 */ 82