Line data    Source code

       1             : /*-------------------------------------------------------------------------
       2             :  *
       3             :  * waitfuncs.c
       4             :  *      Functions for SQL access to syntheses of multiple contention types.
       5             :  *
       6             :  * Copyright (c) 2002-2024, PostgreSQL Global Development Group
       7             :  *
       8             :  * IDENTIFICATION
       9             :  *      src/backend/utils/adt/waitfuncs.c
      10             :  *
      11             :  *-------------------------------------------------------------------------
      12             :  */
      13             : #include "postgres.h"
      14             : 
      15             : #include "catalog/pg_type.h"
      16             : #include "storage/predicate_internals.h"
      17             : #include "storage/proc.h"
      18             : #include "storage/procarray.h"
      19             : #include "utils/array.h"
      20             : #include "utils/builtins.h"
      21             : #include "utils/wait_event.h"
      22             : 
      23             : #define UINT32_ACCESS_ONCE(var)      ((uint32)(*((volatile uint32 *)&(var))))
      24             : 
      25             : 
      26             : /*
      27             :  * pg_isolation_test_session_is_blocked - support function for isolationtester
      28             :  *
      29             :  * Check if specified PID is blocked by any of the PIDs listed in the second
      30             :  * argument.  Currently, this looks for blocking caused by waiting for
      31             :  * injection points, heavyweight locks, or safe snapshots.  We ignore blockage
      32             :  * caused by PIDs not directly under the isolationtester's control, eg
      33             :  * autovacuum.
      34             :  *
      35             :  * This is an undocumented function intended for use by the isolation tester,
      36             :  * and may change in future releases as required for testing purposes.
      37             :  */
      38             : Datum
      39        2982 : pg_isolation_test_session_is_blocked(PG_FUNCTION_ARGS)
      40             : {
      41        2982 :     int         blocked_pid = PG_GETARG_INT32(0);
      42        2982 :     ArrayType  *interesting_pids_a = PG_GETARG_ARRAYTYPE_P(1);
      43             :     PGPROC     *proc;
      44             :     const char *wait_event_type;
      45             :     ArrayType  *blocking_pids_a;
      46             :     int32      *interesting_pids;
      47             :     int32      *blocking_pids;
      48             :     int         num_interesting_pids;
      49             :     int         num_blocking_pids;
      50             :     int         dummy;
      51             :     int         i,
      52             :                 j;
      53             : 
      54             :     /* Check if blocked_pid is in an injection point. */
      55        2982 :     proc = BackendPidGetProc(blocked_pid);
      56        2982 :     if (proc == NULL)
      57           0 :         PG_RETURN_BOOL(false);  /* session gone: definitely unblocked */
      58             :     wait_event_type =
      59        2982 :         pgstat_get_wait_event_type(UINT32_ACCESS_ONCE(proc->wait_event_info));
      60        2982 :     if (wait_event_type && strcmp("InjectionPoint", wait_event_type) == 0)
      61           0 :         PG_RETURN_BOOL(true);
      62             : 
      63             :     /* Validate the passed-in array */
      64             :     Assert(ARR_ELEMTYPE(interesting_pids_a) == INT4OID);
      65        2982 :     if (array_contains_nulls(interesting_pids_a))
      66           0 :         elog(ERROR, "array must not contain nulls");
      67        2982 :     interesting_pids = (int32 *) ARR_DATA_PTR(interesting_pids_a);
      68        2982 :     num_interesting_pids = ArrayGetNItems(ARR_NDIM(interesting_pids_a),
      69             :                                           ARR_DIMS(interesting_pids_a));
      70             : 
      71             :     /*
      72             :      * Get the PIDs of all sessions blocking the given session's attempt to
      73             :      * acquire heavyweight locks.
      74             :      */
      75             :     blocking_pids_a =
      76        2982 :         DatumGetArrayTypeP(DirectFunctionCall1(pg_blocking_pids, blocked_pid));
      77             : 
      78             :     Assert(ARR_ELEMTYPE(blocking_pids_a) == INT4OID);
      79             :     Assert(!array_contains_nulls(blocking_pids_a));
      80        2982 :     blocking_pids = (int32 *) ARR_DATA_PTR(blocking_pids_a);
      81        2982 :     num_blocking_pids = ArrayGetNItems(ARR_NDIM(blocking_pids_a),
      82             :                                        ARR_DIMS(blocking_pids_a));
      83             : 
      84             :     /*
      85             :      * Check if any of these are in the list of interesting PIDs, that being
      86             :      * the sessions that the isolation tester is running.  We don't use
      87             :      * "arrayoverlaps" here, because it would lead to cache lookups and one of
      88             :      * our goals is to run quickly with debug_discard_caches > 0.  We expect
      89             :      * blocking_pids to be usually empty and otherwise a very small number in
      90             :      * isolation tester cases, so make that the outer loop of a naive search
      91             :      * for a match.
      92             :      */
      93        2982 :     for (i = 0; i < num_blocking_pids; i++)
      94        3394 :         for (j = 0; j < num_interesting_pids; j++)
      95             :         {
      96        3394 :             if (blocking_pids[i] == interesting_pids[j])
      97        2232 :                 PG_RETURN_BOOL(true);
      98             :         }
      99             : 
     100             :     /*
     101             :      * Check if blocked_pid is waiting for a safe snapshot.  We could in
     102             :      * theory check the resulting array of blocker PIDs against the
     103             :      * interesting PIDs list, but since there is no danger of autovacuum
     104             :      * blocking GetSafeSnapshot there seems to be no point in expending cycles
     105             :      * on allocating a buffer and searching for overlap; so it's presently
     106             :      * sufficient for the isolation tester's purposes to use a single element
     107             :      * buffer and check if the number of safe snapshot blockers is non-zero.
     108             :      */
     109         750 :     if (GetSafeSnapshotBlockingPids(blocked_pid, &dummy, 1) > 0)
     110           4 :         PG_RETURN_BOOL(true);
     111             : 
     112         746 :     PG_RETURN_BOOL(false);
     113             : }