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) 1996-2016, 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 bool ShmemAddrIsValid(const void *addr); 39 extern void InitShmemIndex(void); 40 extern HTAB *ShmemInitHash(const char *name, long init_size, long max_size, 41 HASHCTL *infoP, int hash_flags); 42 extern void *ShmemInitStruct(const char *name, Size size, bool *foundPtr); 43 extern Size add_size(Size s1, Size s2); 44 extern Size mul_size(Size s1, Size s2); 45 46 /* ipci.c */ 47 extern void RequestAddinShmemSpace(Size size); 48 49 /* size constants for the shmem index table */ 50 /* max size of data structure string name */ 51 #define SHMEM_INDEX_KEYSIZE (48) 52 /* estimated size of the shmem index table (not a hard limit) */ 53 #define SHMEM_INDEX_SIZE (64) 54 55 /* this is a hash bucket in the shmem index table */ 56 typedef struct 57 { 58 char key[SHMEM_INDEX_KEYSIZE]; /* string name */ 59 void *location; /* location in shared mem */ 60 Size size; /* # bytes allocated for the structure */ 61 } ShmemIndexEnt; 62 63 /* 64 * prototypes for functions in shmqueue.c 65 */ 66 extern void SHMQueueInit(SHM_QUEUE *queue); 67 extern void SHMQueueElemInit(SHM_QUEUE *queue); 68 extern void SHMQueueDelete(SHM_QUEUE *queue); 69 extern void SHMQueueInsertBefore(SHM_QUEUE *queue, SHM_QUEUE *elem); 70 extern void SHMQueueInsertAfter(SHM_QUEUE *queue, SHM_QUEUE *elem); 71 extern Pointer SHMQueueNext(const SHM_QUEUE *queue, const SHM_QUEUE *curElem, 72 Size linkOffset); 73 extern Pointer SHMQueuePrev(const SHM_QUEUE *queue, const SHM_QUEUE *curElem, 74 Size linkOffset); 75 extern bool SHMQueueEmpty(const SHM_QUEUE *queue); 76 extern bool SHMQueueIsDetached(const SHM_QUEUE *queue); 77 78 #endif /* SHMEM_H */ 79