sharedfileset.c

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/*-------------------------------------------------------------------------
 *
 * sharedfileset.c
 *    Shared temporary file management.
 *
 * Portions Copyright (c) 1996-2024, PostgreSQL Global Development Group
 * Portions Copyright (c) 1994, Regents of the University of California
 *
 * IDENTIFICATION
 *    src/backend/storage/file/sharedfileset.c
 *
 * SharedFileSets provide a temporary namespace (think directory) so that
 * files can be discovered by name, and a shared ownership semantics so that
 * shared files survive until the last user detaches.
 *
 *-------------------------------------------------------------------------
 */
 
#include "postgres.h"
 
#include <limits.h>
 
#include "storage/dsm.h"
#include "storage/sharedfileset.h"
 
static void SharedFileSetOnDetach(dsm_segment *segment, Datum datum);
 
/*
 * Initialize a space for temporary files that can be opened by other backends.
 * Other backends must attach to it before accessing it.  Associate this
 * SharedFileSet with 'seg'.  Any contained files will be deleted when the
 * last backend detaches.
 *
 * Under the covers the set is one or more directories which will eventually
 * be deleted.
 */
void
SharedFileSetInit(SharedFileSet *fileset, dsm_segment *seg)
{
    /* Initialize the shared fileset specific members. */
    SpinLockInit(&fileset->mutex);
    fileset->refcnt = 1;
 
    /* Initialize the fileset. */
    FileSetInit(&fileset->fs);
 
    /* Register our cleanup callback. */
    if (seg)
        on_dsm_detach(seg, SharedFileSetOnDetach, PointerGetDatum(fileset));
}
 
/*
 * Attach to a set of directories that was created with SharedFileSetInit.
 */
void
SharedFileSetAttach(SharedFileSet *fileset, dsm_segment *seg)
{
    bool        success;
 
    SpinLockAcquire(&fileset->mutex);
    if (fileset->refcnt == 0)
        success = false;
    else
    {
        ++fileset->refcnt;
        success = true;
    }
    SpinLockRelease(&fileset->mutex);
 
    if (!success)
        ereport(ERROR,
                (errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
                 errmsg("could not attach to a SharedFileSet that is already destroyed")));
 
    /* Register our cleanup callback. */
    on_dsm_detach(seg, SharedFileSetOnDetach, PointerGetDatum(fileset));
}
 
/*
 * Delete all files in the set.
 */
void
SharedFileSetDeleteAll(SharedFileSet *fileset)
{
    FileSetDeleteAll(&fileset->fs);
}
 
/*
 * Callback function that will be invoked when this backend detaches from a
 * DSM segment holding a SharedFileSet that it has created or attached to.  If
 * we are the last to detach, then try to remove the directories and
 * everything in them.  We can't raise an error on failures, because this runs
 * in error cleanup paths.
 */
static void
SharedFileSetOnDetach(dsm_segment *segment, Datum datum)
{
    bool        unlink_all = false;
    SharedFileSet *fileset = (SharedFileSet *) DatumGetPointer(datum);
 
    SpinLockAcquire(&fileset->mutex);
    Assert(fileset->refcnt > 0);
    if (--fileset->refcnt == 0)
        unlink_all = true;
    SpinLockRelease(&fileset->mutex);
 
    /*
     * If we are the last to detach, we delete the directory in all
     * tablespaces.  Note that we are still actually attached for the rest of
     * this function so we can safely access its data.
     */
    if (unlink_all)
        FileSetDeleteAll(&fileset->fs);
}