Line data    Source code

       1             : /*-------------------------------------------------------------------------
       2             :  *
       3             :  * sharedfileset.c
       4             :  *    Shared temporary file management.
       5             :  *
       6             :  * Portions Copyright (c) 1996-2025, PostgreSQL Global Development Group
       7             :  * Portions Copyright (c) 1994, Regents of the University of California
       8             :  *
       9             :  * IDENTIFICATION
      10             :  *    src/backend/storage/file/sharedfileset.c
      11             :  *
      12             :  * SharedFileSets provide a temporary namespace (think directory) so that
      13             :  * files can be discovered by name, and a shared ownership semantics so that
      14             :  * shared files survive until the last user detaches.
      15             :  *
      16             :  *-------------------------------------------------------------------------
      17             :  */
      18             : 
      19             : #include "postgres.h"
      20             : 
      21             : #include <limits.h>
      22             : 
      23             : #include "storage/dsm.h"
      24             : #include "storage/sharedfileset.h"
      25             : 
      26             : static void SharedFileSetOnDetach(dsm_segment *segment, Datum datum);
      27             : 
      28             : /*
      29             :  * Initialize a space for temporary files that can be opened by other backends.
      30             :  * Other backends must attach to it before accessing it.  Associate this
      31             :  * SharedFileSet with 'seg'.  Any contained files will be deleted when the
      32             :  * last backend detaches.
      33             :  *
      34             :  * Under the covers the set is one or more directories which will eventually
      35             :  * be deleted.
      36             :  */
      37             : void
      38         342 : SharedFileSetInit(SharedFileSet *fileset, dsm_segment *seg)
      39             : {
      40             :     /* Initialize the shared fileset specific members. */
      41         342 :     SpinLockInit(&fileset->mutex);
      42         342 :     fileset->refcnt = 1;
      43             : 
      44             :     /* Initialize the fileset. */
      45         342 :     FileSetInit(&fileset->fs);
      46             : 
      47             :     /* Register our cleanup callback. */
      48         342 :     if (seg)
      49         342 :         on_dsm_detach(seg, SharedFileSetOnDetach, PointerGetDatum(fileset));
      50         342 : }
      51             : 
      52             : /*
      53             :  * Attach to a set of directories that was created with SharedFileSetInit.
      54             :  */
      55             : void
      56         530 : SharedFileSetAttach(SharedFileSet *fileset, dsm_segment *seg)
      57             : {
      58             :     bool        success;
      59             : 
      60         530 :     SpinLockAcquire(&fileset->mutex);
      61         530 :     if (fileset->refcnt == 0)
      62           0 :         success = false;
      63             :     else
      64             :     {
      65         530 :         ++fileset->refcnt;
      66         530 :         success = true;
      67             :     }
      68         530 :     SpinLockRelease(&fileset->mutex);
      69             : 
      70         530 :     if (!success)
      71           0 :         ereport(ERROR,
      72             :                 (errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
      73             :                  errmsg("could not attach to a SharedFileSet that is already destroyed")));
      74             : 
      75             :     /* Register our cleanup callback. */
      76         530 :     on_dsm_detach(seg, SharedFileSetOnDetach, PointerGetDatum(fileset));
      77         530 : }
      78             : 
      79             : /*
      80             :  * Delete all files in the set.
      81             :  */
      82             : void
      83          48 : SharedFileSetDeleteAll(SharedFileSet *fileset)
      84             : {
      85          48 :     FileSetDeleteAll(&fileset->fs);
      86          48 : }
      87             : 
      88             : /*
      89             :  * Callback function that will be invoked when this backend detaches from a
      90             :  * DSM segment holding a SharedFileSet that it has created or attached to.  If
      91             :  * we are the last to detach, then try to remove the directories and
      92             :  * everything in them.  We can't raise an error on failures, because this runs
      93             :  * in error cleanup paths.
      94             :  */
      95             : static void
      96         872 : SharedFileSetOnDetach(dsm_segment *segment, Datum datum)
      97             : {
      98         872 :     bool        unlink_all = false;
      99         872 :     SharedFileSet *fileset = (SharedFileSet *) DatumGetPointer(datum);
     100             : 
     101         872 :     SpinLockAcquire(&fileset->mutex);
     102             :     Assert(fileset->refcnt > 0);
     103         872 :     if (--fileset->refcnt == 0)
     104         342 :         unlink_all = true;
     105         872 :     SpinLockRelease(&fileset->mutex);
     106             : 
     107             :     /*
     108             :      * If we are the last to detach, we delete the directory in all
     109             :      * tablespaces.  Note that we are still actually attached for the rest of
     110             :      * this function so we can safely access its data.
     111             :      */
     112         872 :     if (unlink_all)
     113         342 :         FileSetDeleteAll(&fileset->fs);
     114         872 : }