dsm.c

/*-------------------------------------------------------------------------
 *
 * dsm.c
 *	  manage dynamic shared memory segments
 *
 * This file provides a set of services to make programming with dynamic
 * shared memory segments more convenient.  Unlike the low-level
 * facilities provided by dsm_impl.h and dsm_impl.c, mappings and segments
 * created using this module will be cleaned up automatically.  Mappings
 * will be removed when the resource owner under which they were created
 * is cleaned up, unless dsm_pin_mapping() is used, in which case they
 * have session lifespan.  Segments will be removed when there are no
 * remaining mappings, or at postmaster shutdown in any case.  After a
 * hard postmaster crash, remaining segments will be removed, if they
 * still exist, at the next postmaster startup.
 *
 * Portions Copyright (c) 1996-2015, PostgreSQL Global Development Group
 * Portions Copyright (c) 1994, Regents of the University of California
 *
 *
 * IDENTIFICATION
 *	  src/backend/storage/ipc/dsm.c
 *
 *-------------------------------------------------------------------------
 */

#include "postgres.h"

#include <fcntl.h>
#include <string.h>
#include <unistd.h>
#ifndef WIN32
#include <sys/mman.h>
#endif
#include <sys/stat.h>

#include "lib/ilist.h"
#include "miscadmin.h"
#include "storage/dsm.h"
#include "storage/ipc.h"
#include "storage/lwlock.h"
#include "storage/pg_shmem.h"
#include "utils/guc.h"
#include "utils/memutils.h"
#include "utils/resowner_private.h"

#define PG_DYNSHMEM_CONTROL_MAGIC		0x9a503d32

/*
 * There's no point in getting too cheap here, because the minimum allocation
 * is one OS page, which is probably at least 4KB and could easily be as high
 * as 64KB.  Each currently sizeof(dsm_control_item), currently 8 bytes.
 */
#define PG_DYNSHMEM_FIXED_SLOTS			64
#define PG_DYNSHMEM_SLOTS_PER_BACKEND	2

#define INVALID_CONTROL_SLOT		((uint32) -1)

/* Backend-local tracking for on-detach callbacks. */
typedef struct dsm_segment_detach_callback
{
	on_dsm_detach_callback function;
	Datum		arg;
	slist_node	node;
} dsm_segment_detach_callback;

/* Backend-local state for a dynamic shared memory segment. */
struct dsm_segment
{
	dlist_node	node;			/* List link in dsm_segment_list. */