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/*-------------------------------------------------------------------------
*
* sharedfileset.c
* Shared temporary file management.
*
* Portions Copyright (c) 1996-2023, 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 "catalog/pg_tablespace.h"
#include "commands/tablespace.h"
#include "common/hashfn.h"
#include "miscadmin.h"
#include "storage/dsm.h"
#include "storage/ipc.h"
#include "storage/sharedfileset.h"
#include "utils/builtins.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);
}
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