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/*-------------------------------------------------------------------------
*
* pg_shmem.h
* Platform-independent API for shared memory support.
*
* Every port is expected to support shared memory with approximately
* SysV-ish semantics; in particular, a memory block is not anonymous
* but has an ID, and we must be able to tell whether there are any
* remaining processes attached to a block of a specified ID.
*
* To simplify life for the SysV implementation, the ID is assumed to
* consist of two unsigned long values (these are key and ID in SysV
* terms). Other platforms may ignore the second value if they need
* only one ID number.
*
*
* Portions Copyright (c) 1996-2020, PostgreSQL Global Development Group
* Portions Copyright (c) 1994, Regents of the University of California
*
* src/include/storage/pg_shmem.h
*
*-------------------------------------------------------------------------
*/
#ifndef PG_SHMEM_H
#define PG_SHMEM_H
#include "storage/dsm_impl.h"
typedef struct PGShmemHeader /* standard header for all Postgres shmem */
{
int32 magic; /* magic # to identify Postgres segments */
#define PGShmemMagic 679834894
pid_t creatorPID; /* PID of creating process (set but unread) */
Size totalsize; /* total size of segment */
Size freeoffset; /* offset to first free space */
dsm_handle dsm_control; /* ID of dynamic shared memory control seg */
void *index; /* pointer to ShmemIndex table */
#ifndef WIN32 /* Windows doesn't have useful inode#s */
dev_t device; /* device data directory is on */
ino_t inode; /* inode number of data directory */
#endif
} PGShmemHeader;
/* GUC variables */
extern int shared_memory_type;
extern int huge_pages;
/* Possible values for huge_pages */
typedef enum
{
HUGE_PAGES_OFF,
HUGE_PAGES_ON,
HUGE_PAGES_TRY
} HugePagesType;
/* Possible values for shared_memory_type */
typedef enum
{
SHMEM_TYPE_WINDOWS,
SHMEM_TYPE_SYSV,
SHMEM_TYPE_MMAP
} PGShmemType;
#ifndef WIN32
extern unsigned long UsedShmemSegID;
#else
extern HANDLE UsedShmemSegID;
extern void *ShmemProtectiveRegion;
#endif
extern void *UsedShmemSegAddr;
#if !defined(WIN32) && !defined(EXEC_BACKEND)
#define DEFAULT_SHARED_MEMORY_TYPE SHMEM_TYPE_MMAP
#elif !defined(WIN32)
#define DEFAULT_SHARED_MEMORY_TYPE SHMEM_TYPE_SYSV
#else
#define DEFAULT_SHARED_MEMORY_TYPE SHMEM_TYPE_WINDOWS
#endif
#ifdef EXEC_BACKEND
extern void PGSharedMemoryReAttach(void);
extern void PGSharedMemoryNoReAttach(void);
#endif
extern PGShmemHeader *PGSharedMemoryCreate(Size size,
PGShmemHeader **shim);
extern bool PGSharedMemoryIsInUse(unsigned long id1, unsigned long id2);
extern void PGSharedMemoryDetach(void);
#endif /* PG_SHMEM_H */
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