dsm_impl.h

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/*-------------------------------------------------------------------------
 *
 * dsm_impl.h
 *    low-level dynamic shared memory primitives
 *
 * Portions Copyright (c) 1996-2025, PostgreSQL Global Development Group
 * Portions Copyright (c) 1994, Regents of the University of California
 *
 * src/include/storage/dsm_impl.h
 *
 *-------------------------------------------------------------------------
 */
#ifndef DSM_IMPL_H
#define DSM_IMPL_H
 
/* Dynamic shared memory implementations. */
#define DSM_IMPL_POSIX          1
#define DSM_IMPL_SYSV           2
#define DSM_IMPL_WINDOWS        3
#define DSM_IMPL_MMAP           4
 
/*
 * Determine which dynamic shared memory implementations will be supported
 * on this platform, and which one will be the default.
 */
#ifdef WIN32
#define USE_DSM_WINDOWS
#define DEFAULT_DYNAMIC_SHARED_MEMORY_TYPE      DSM_IMPL_WINDOWS
#else
#ifdef HAVE_SHM_OPEN
#define USE_DSM_POSIX
#define DEFAULT_DYNAMIC_SHARED_MEMORY_TYPE      DSM_IMPL_POSIX
#endif
#define USE_DSM_SYSV
#ifndef DEFAULT_DYNAMIC_SHARED_MEMORY_TYPE
#define DEFAULT_DYNAMIC_SHARED_MEMORY_TYPE      DSM_IMPL_SYSV
#endif
#define USE_DSM_MMAP
#endif
 
/* GUC. */
extern PGDLLIMPORT int dynamic_shared_memory_type;
extern PGDLLIMPORT int min_dynamic_shared_memory;
 
/*
 * Directory for on-disk state.
 *
 * This is used by all implementations for crash recovery and by the mmap
 * implementation for storage.
 */
#define PG_DYNSHMEM_DIR                 "pg_dynshmem"
#define PG_DYNSHMEM_MMAP_FILE_PREFIX    "mmap."
 
/* A "name" for a dynamic shared memory segment. */
typedef uint32 dsm_handle;
 
/* Sentinel value to use for invalid DSM handles. */
#define DSM_HANDLE_INVALID ((dsm_handle) 0)
 
/* All the shared-memory operations we know about. */
typedef enum
{
    DSM_OP_CREATE,
    DSM_OP_ATTACH,
    DSM_OP_DETACH,
    DSM_OP_DESTROY,
} dsm_op;
 
/* Create, attach to, detach from, resize, or destroy a segment. */
extern bool dsm_impl_op(dsm_op op, dsm_handle handle, Size request_size,
                        void **impl_private, void **mapped_address, Size *mapped_size,
                        int elevel);
 
/* Implementation-dependent actions required to keep segment until shutdown. */
extern void dsm_impl_pin_segment(dsm_handle handle, void *impl_private,
                                 void **impl_private_pm_handle);
extern void dsm_impl_unpin_segment(dsm_handle handle, void **impl_private);
 
#endif                          /* DSM_IMPL_H */