pg_shmem.h File Reference

#include "storage/dsm_impl.h"

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Data Structures
struct	PGShmemHeader

Macros
#define	PGShmemMagic   679834894
#define	DEFAULT_SHARED_MEMORY_TYPE   SHMEM_TYPE_MMAP

Typedefs
typedef struct PGShmemHeader	PGShmemHeader

Enumerations
enum	HugePagesType { HUGE_PAGES_OFF , HUGE_PAGES_ON , HUGE_PAGES_TRY , HUGE_PAGES_UNKNOWN }
enum	PGShmemType { SHMEM_TYPE_WINDOWS , SHMEM_TYPE_SYSV , SHMEM_TYPE_MMAP }

Functions
PGShmemHeader *	PGSharedMemoryCreate (Size size, PGShmemHeader **shim)
bool	PGSharedMemoryIsInUse (unsigned long id1, unsigned long id2)
void	PGSharedMemoryDetach (void)
void	GetHugePageSize (Size *hugepagesize, int *mmap_flags)

Variables
PGDLLIMPORT int	shared_memory_type
PGDLLIMPORT int	huge_pages
PGDLLIMPORT int	huge_page_size
PGDLLIMPORT unsigned long	UsedShmemSegID
PGDLLIMPORT void *	UsedShmemSegAddr

Macro Definition Documentation

DEFAULT_SHARED_MEMORY_TYPE

#define DEFAULT_SHARED_MEMORY_TYPE   SHMEM_TYPE_MMAP

Definition at line 75 of file pg_shmem.h.

PGShmemMagic

#define PGShmemMagic   679834894

Definition at line 32 of file pg_shmem.h.

Typedef Documentation

PGShmemHeader

typedef struct PGShmemHeader PGShmemHeader

Enumeration Type Documentation

HugePagesType

enum HugePagesType

Enumerator
HUGE_PAGES_OFF
HUGE_PAGES_ON
HUGE_PAGES_TRY
HUGE_PAGES_UNKNOWN

Definition at line 50 of file pg_shmem.h.

{
    HUGE_PAGES_OFF,
    HUGE_PAGES_ON,
    HUGE_PAGES_TRY,             /* only for huge_pages */
    HUGE_PAGES_UNKNOWN,         /* only for huge_pages_status */
}           HugePagesType;

PGShmemType

enum PGShmemType

Enumerator
SHMEM_TYPE_WINDOWS
SHMEM_TYPE_SYSV
SHMEM_TYPE_MMAP

Definition at line 59 of file pg_shmem.h.

{
    SHMEM_TYPE_WINDOWS,
    SHMEM_TYPE_SYSV,
    SHMEM_TYPE_MMAP,
}           PGShmemType;

Function Documentation

GetHugePageSize()

void GetHugePageSize	(	Size *	hugepagesize,
		int *	mmap_flags
	)

Definition at line 479 of file sysv_shmem.c.

{
#ifdef MAP_HUGETLB
 
    Size        default_hugepagesize = 0;
    Size        hugepagesize_local = 0;
    int         mmap_flags_local = 0;
 
    /*
     * System-dependent code to find out the default huge page size.
     *
     * On Linux, read /proc/meminfo looking for a line like "Hugepagesize:
     * nnnn kB".  Ignore any failures, falling back to the preset default.
     */
#ifdef __linux__
 
    {
        FILE       *fp = AllocateFile("/proc/meminfo", "r");
        char        buf[128];
        unsigned int sz;
        char        ch;
 
        if (fp)
        {
            while (fgets(buf, sizeof(buf), fp))
            {
                if (sscanf(buf, "Hugepagesize: %u %c", &sz, &ch) == 2)
                {
                    if (ch == 'k')
                    {
                        default_hugepagesize = sz * (Size) 1024;
                        break;
                    }
                    /* We could accept other units besides kB, if needed */
                }
            }
            FreeFile(fp);
        }
    }
#endif                          /* __linux__ */
 
    if (huge_page_size != 0)
    {
        /* If huge page size is requested explicitly, use that. */
        hugepagesize_local = (Size) huge_page_size * 1024;
    }
    else if (default_hugepagesize != 0)
    {
        /* Otherwise use the system default, if we have it. */
        hugepagesize_local = default_hugepagesize;
    }
    else
    {
        /*
         * If we fail to find out the system's default huge page size, or no
         * huge page size is requested explicitly, assume it is 2MB. This will
         * work fine when the actual size is less.  If it's more, we might get
         * mmap() or munmap() failures due to unaligned requests; but at this
         * writing, there are no reports of any non-Linux systems being picky
         * about that.
         */
        hugepagesize_local = 2 * 1024 * 1024;
    }
 
    mmap_flags_local = MAP_HUGETLB;
 
    /*
     * On recent enough Linux, also include the explicit page size, if
     * necessary.
     */
#if defined(MAP_HUGE_MASK) && defined(MAP_HUGE_SHIFT)
    if (hugepagesize_local != default_hugepagesize)
    {
        int         shift = pg_ceil_log2_64(hugepagesize_local);
 
        mmap_flags_local |= (shift & MAP_HUGE_MASK) << MAP_HUGE_SHIFT;
    }
#endif
 
    /* assign the results found */
    if (mmap_flags)
        *mmap_flags = mmap_flags_local;
    if (hugepagesize)
        *hugepagesize = hugepagesize_local;
 
#else
 
    if (hugepagesize)
        *hugepagesize = 0;
    if (mmap_flags)
        *mmap_flags = 0;
 
#endif                          /* MAP_HUGETLB */
}

References AllocateFile(), buf, FreeFile(), huge_page_size, and pg_ceil_log2_64().

Referenced by CreateAnonymousSegment(), and InitializeShmemGUCs().

PGSharedMemoryCreate()

PGShmemHeader* PGSharedMemoryCreate	(	Size	size,
		PGShmemHeader **	shim
	)

Definition at line 700 of file sysv_shmem.c.

{
    IpcMemoryKey NextShmemSegID;
    void       *memAddress;
    PGShmemHeader *hdr;
    struct stat statbuf;
    Size        sysvsize;
 
    /*
     * We use the data directory's ID info (inode and device numbers) to
     * positively identify shmem segments associated with this data dir, and
     * also as seeds for searching for a free shmem key.
     */
    if (stat(DataDir, &statbuf) < 0)
        ereport(FATAL,
                (errcode_for_file_access(),
                 errmsg("could not stat data directory \"%s\": %m",
                        DataDir)));
 
    /* Complain if hugepages demanded but we can't possibly support them */
#if !defined(MAP_HUGETLB)
    if (huge_pages == HUGE_PAGES_ON)
        ereport(ERROR,
                (errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
                 errmsg("huge pages not supported on this platform")));
#endif
 
    /* For now, we don't support huge pages in SysV memory */
    if (huge_pages == HUGE_PAGES_ON && shared_memory_type != SHMEM_TYPE_MMAP)
        ereport(ERROR,
                (errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
                 errmsg("huge pages not supported with the current \"shared_memory_type\" setting")));
 
    /* Room for a header? */
    Assert(size > MAXALIGN(sizeof(PGShmemHeader)));
 
    if (shared_memory_type == SHMEM_TYPE_MMAP)
    {
        AnonymousShmem = CreateAnonymousSegment(&size);
        AnonymousShmemSize = size;
 
        /* Register on-exit routine to unmap the anonymous segment */
        on_shmem_exit(AnonymousShmemDetach, (Datum) 0);
 
        /* Now we need only allocate a minimal-sized SysV shmem block. */
        sysvsize = sizeof(PGShmemHeader);
    }
    else
    {
        sysvsize = size;
 
        /* huge pages are only available with mmap */
        SetConfigOption("huge_pages_status", "off",
                        PGC_INTERNAL, PGC_S_DYNAMIC_DEFAULT);
    }
 
    /*
     * Loop till we find a free IPC key.  Trust CreateDataDirLockFile() to
     * ensure no more than one postmaster per data directory can enter this
     * loop simultaneously.  (CreateDataDirLockFile() does not entirely ensure
     * that, but prefer fixing it over coping here.)
     */
    NextShmemSegID = statbuf.st_ino;
 
    for (;;)
    {
        IpcMemoryId shmid;
        PGShmemHeader *oldhdr;
        IpcMemoryState state;
 
        /* Try to create new segment */
        memAddress = InternalIpcMemoryCreate(NextShmemSegID, sysvsize);
        if (memAddress)
            break;              /* successful create and attach */
 
        /* Check shared memory and possibly remove and recreate */
 
        /*
         * shmget() failure is typically EACCES, hence SHMSTATE_FOREIGN.
         * ENOENT, a narrow possibility, implies SHMSTATE_ENOENT, but one can
         * safely treat SHMSTATE_ENOENT like SHMSTATE_FOREIGN.
         */
        shmid = shmget(NextShmemSegID, sizeof(PGShmemHeader), 0);
        if (shmid < 0)
        {
            oldhdr = NULL;
            state = SHMSTATE_FOREIGN;
        }
        else
            state = PGSharedMemoryAttach(shmid, NULL, &oldhdr);
 
        switch (state)
        {
            case SHMSTATE_ANALYSIS_FAILURE:
            case SHMSTATE_ATTACHED:
                ereport(FATAL,
                        (errcode(ERRCODE_LOCK_FILE_EXISTS),
                         errmsg("pre-existing shared memory block (key %lu, ID %lu) is still in use",
                                (unsigned long) NextShmemSegID,
                                (unsigned long) shmid),
                         errhint("Terminate any old server processes associated with data directory \"%s\".",
                                 DataDir)));
                break;
            case SHMSTATE_ENOENT:
 
                /*
                 * To our surprise, some other process deleted since our last
                 * InternalIpcMemoryCreate().  Moments earlier, we would have
                 * seen SHMSTATE_FOREIGN.  Try that same ID again.
                 */
                elog(LOG,
                     "shared memory block (key %lu, ID %lu) deleted during startup",
                     (unsigned long) NextShmemSegID,
                     (unsigned long) shmid);
                break;
            case SHMSTATE_FOREIGN:
                NextShmemSegID++;
                break;
            case SHMSTATE_UNATTACHED:
 
                /*
                 * The segment pertains to DataDir, and every process that had
                 * used it has died or detached.  Zap it, if possible, and any
                 * associated dynamic shared memory segments, as well.  This
                 * shouldn't fail, but if it does, assume the segment belongs
                 * to someone else after all, and try the next candidate.
                 * Otherwise, try again to create the segment.  That may fail
                 * if some other process creates the same shmem key before we
                 * do, in which case we'll try the next key.
                 */
                if (oldhdr->dsm_control != 0)
                    dsm_cleanup_using_control_segment(oldhdr->dsm_control);
                if (shmctl(shmid, IPC_RMID, NULL) < 0)
                    NextShmemSegID++;
                break;
        }
 
        if (oldhdr && shmdt(oldhdr) < 0)
            elog(LOG, "shmdt(%p) failed: %m", oldhdr);
    }
 
    /* Initialize new segment. */
    hdr = (PGShmemHeader *) memAddress;
    hdr->creatorPID = getpid();
    hdr->magic = PGShmemMagic;
    hdr->dsm_control = 0;
 
    /* Fill in the data directory ID info, too */
    hdr->device = statbuf.st_dev;
    hdr->inode = statbuf.st_ino;
 
    /*
     * Initialize space allocation status for segment.
     */
    hdr->totalsize = size;
    hdr->freeoffset = MAXALIGN(sizeof(PGShmemHeader));
    *shim = hdr;
 
    /* Save info for possible future use */
    UsedShmemSegAddr = memAddress;
    UsedShmemSegID = (unsigned long) NextShmemSegID;
 
    /*
     * If AnonymousShmem is NULL here, then we're not using anonymous shared
     * memory, and should return a pointer to the System V shared memory
     * block. Otherwise, the System V shared memory block is only a shim, and
     * we must return a pointer to the real block.
     */
    if (AnonymousShmem == NULL)
        return hdr;
    memcpy(AnonymousShmem, hdr, sizeof(PGShmemHeader));
    return (PGShmemHeader *) AnonymousShmem;
}

References AnonymousShmem, AnonymousShmemDetach(), AnonymousShmemSize, Assert, CreateAnonymousSegment(), PGShmemHeader::creatorPID, DataDir, DEBUG1, PGShmemHeader::device, dsm_cleanup_using_control_segment(), PGShmemHeader::dsm_control, elog, EnableLockPagesPrivilege(), ereport, errcode(), errcode_for_file_access(), errdetail(), errhint(), errmsg(), errmsg_internal(), ERROR, FATAL, free, PGShmemHeader::freeoffset, GetSharedMemName(), huge_pages, HUGE_PAGES_ON, HUGE_PAGES_TRY, i, PGShmemHeader::inode, InternalIpcMemoryCreate(), IPC_RMID, LOG, PGShmemHeader::magic, MAXALIGN, on_shmem_exit(), PGC_INTERNAL, PGC_S_DYNAMIC_DEFAULT, PGSharedMemoryAttach(), PGShmemMagic, pgwin32_SharedMemoryDelete(), PointerGetDatum(), PROTECTIVE_REGION_SIZE, SetConfigOption(), shared_memory_type, SHMEM_TYPE_MMAP, ShmemProtectiveRegion, SHMSTATE_ANALYSIS_FAILURE, SHMSTATE_ATTACHED, SHMSTATE_ENOENT, SHMSTATE_FOREIGN, SHMSTATE_UNATTACHED, size, stat::st_dev, stat::st_ino, stat, PGShmemHeader::totalsize, UsedShmemSegAddr, UsedShmemSegID, and UsedShmemSegSize.

Referenced by CreateSharedMemoryAndSemaphores().

PGSharedMemoryDetach()

void PGSharedMemoryDetach

(

void

)

Definition at line 970 of file sysv_shmem.c.

{
    if (UsedShmemSegAddr != NULL)
    {
        if ((shmdt(UsedShmemSegAddr) < 0)
#if defined(EXEC_BACKEND) && defined(__CYGWIN__)
        /* Work-around for cygipc exec bug */
            && shmdt(NULL) < 0
#endif
            )
            elog(LOG, "shmdt(%p) failed: %m", UsedShmemSegAddr);
        UsedShmemSegAddr = NULL;
    }
 
    if (AnonymousShmem != NULL)
    {
        if (munmap(AnonymousShmem, AnonymousShmemSize) < 0)
            elog(LOG, "munmap(%p, %zu) failed: %m",
                 AnonymousShmem, AnonymousShmemSize);
        AnonymousShmem = NULL;
    }
}

References AnonymousShmem, AnonymousShmemSize, elog, LOG, ShmemProtectiveRegion, UsedShmemSegAddr, and UsedShmemSegID.

Referenced by PGSharedMemoryNoReAttach(), pgwin32_SharedMemoryDelete(), and postmaster_child_launch().

PGSharedMemoryIsInUse()

bool PGSharedMemoryIsInUse	(	unsigned long	id1,
		unsigned long	id2
	)

Definition at line 317 of file sysv_shmem.c.

{
    PGShmemHeader *memAddress;
    IpcMemoryState state;
 
    state = PGSharedMemoryAttach((IpcMemoryId) id2, NULL, &memAddress);
    if (memAddress && shmdt(memAddress) < 0)
        elog(LOG, "shmdt(%p) failed: %m", memAddress);
    switch (state)
    {
        case SHMSTATE_ENOENT:
        case SHMSTATE_FOREIGN:
        case SHMSTATE_UNATTACHED:
            return false;
        case SHMSTATE_ANALYSIS_FAILURE:
        case SHMSTATE_ATTACHED:
            return true;
    }
    return true;
}

References elog, free, GetSharedMemName(), LOG, PGSharedMemoryAttach(), SHMSTATE_ANALYSIS_FAILURE, SHMSTATE_ATTACHED, SHMSTATE_ENOENT, SHMSTATE_FOREIGN, and SHMSTATE_UNATTACHED.

Referenced by CreateLockFile().

Variable Documentation

huge_page_size

PGDLLIMPORT int huge_page_size

extern

Definition at line 563 of file guc_tables.c.

Referenced by GetHugePageSize().

huge_pages

PGDLLIMPORT int huge_pages

extern

Definition at line 562 of file guc_tables.c.

Referenced by CreateAnonymousSegment(), and PGSharedMemoryCreate().

shared_memory_type

PGDLLIMPORT int shared_memory_type

extern

Definition at line 55 of file ipci.c.

Referenced by PGSharedMemoryCreate().

UsedShmemSegAddr

PGDLLIMPORT void* UsedShmemSegAddr

extern

Definition at line 95 of file sysv_shmem.c.

Referenced by PGSharedMemoryCreate(), PGSharedMemoryDetach(), PGSharedMemoryNoReAttach(), PGSharedMemoryReAttach(), and pgwin32_ReserveSharedMemoryRegion().

UsedShmemSegID

PGDLLIMPORT unsigned long UsedShmemSegID

extern

Definition at line 94 of file sysv_shmem.c.

Referenced by PGSharedMemoryCreate(), PGSharedMemoryDetach(), PGSharedMemoryReAttach(), and pgwin32_SharedMemoryDelete().