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/*-------------------------------------------------------------------------
*
* waitfuncs.c
* Functions for SQL access to syntheses of multiple contention types.
*
* Copyright (c) 2002-2024, PostgreSQL Global Development Group
*
* IDENTIFICATION
* src/backend/utils/adt/waitfuncs.c
*
*-------------------------------------------------------------------------
*/
#include "postgres.h"
#include "catalog/pg_type.h"
#include "storage/predicate_internals.h"
#include "storage/proc.h"
#include "storage/procarray.h"
#include "utils/array.h"
#include "utils/fmgrprotos.h"
#include "utils/wait_event.h"
#define UINT32_ACCESS_ONCE(var) ((uint32)(*((volatile uint32 *)&(var))))
/*
* pg_isolation_test_session_is_blocked - support function for isolationtester
*
* Check if specified PID is blocked by any of the PIDs listed in the second
* argument. Currently, this looks for blocking caused by waiting for
* injection points, heavyweight locks, or safe snapshots. We ignore blockage
* caused by PIDs not directly under the isolationtester's control, eg
* autovacuum.
*
* This is an undocumented function intended for use by the isolation tester,
* and may change in future releases as required for testing purposes.
*/
Datum
pg_isolation_test_session_is_blocked(PG_FUNCTION_ARGS)
{
int blocked_pid = PG_GETARG_INT32(0);
ArrayType *interesting_pids_a = PG_GETARG_ARRAYTYPE_P(1);
PGPROC *proc;
const char *wait_event_type;
ArrayType *blocking_pids_a;
int32 *interesting_pids;
int32 *blocking_pids;
int num_interesting_pids;
int num_blocking_pids;
int dummy;
int i,
j;
/* Check if blocked_pid is in an injection point. */
proc = BackendPidGetProc(blocked_pid);
if (proc == NULL)
PG_RETURN_BOOL(false); /* session gone: definitely unblocked */
wait_event_type =
pgstat_get_wait_event_type(UINT32_ACCESS_ONCE(proc->wait_event_info));
if (wait_event_type && strcmp("InjectionPoint", wait_event_type) == 0)
PG_RETURN_BOOL(true);
/* Validate the passed-in array */
Assert(ARR_ELEMTYPE(interesting_pids_a) == INT4OID);
if (array_contains_nulls(interesting_pids_a))
elog(ERROR, "array must not contain nulls");
interesting_pids = (int32 *) ARR_DATA_PTR(interesting_pids_a);
num_interesting_pids = ArrayGetNItems(ARR_NDIM(interesting_pids_a),
ARR_DIMS(interesting_pids_a));
/*
* Get the PIDs of all sessions blocking the given session's attempt to
* acquire heavyweight locks.
*/
blocking_pids_a =
DatumGetArrayTypeP(DirectFunctionCall1(pg_blocking_pids, blocked_pid));
Assert(ARR_ELEMTYPE(blocking_pids_a) == INT4OID);
Assert(!array_contains_nulls(blocking_pids_a));
blocking_pids = (int32 *) ARR_DATA_PTR(blocking_pids_a);
num_blocking_pids = ArrayGetNItems(ARR_NDIM(blocking_pids_a),
ARR_DIMS(blocking_pids_a));
/*
* Check if any of these are in the list of interesting PIDs, that being
* the sessions that the isolation tester is running. We don't use
* "arrayoverlaps" here, because it would lead to cache lookups and one of
* our goals is to run quickly with debug_discard_caches > 0. We expect
* blocking_pids to be usually empty and otherwise a very small number in
* isolation tester cases, so make that the outer loop of a naive search
* for a match.
*/
for (i = 0; i < num_blocking_pids; i++)
for (j = 0; j < num_interesting_pids; j++)
{
if (blocking_pids[i] == interesting_pids[j])
PG_RETURN_BOOL(true);
}
/*
* Check if blocked_pid is waiting for a safe snapshot. We could in
* theory check the resulting array of blocker PIDs against the
* interesting PIDs list, but since there is no danger of autovacuum
* blocking GetSafeSnapshot there seems to be no point in expending cycles
* on allocating a buffer and searching for overlap; so it's presently
* sufficient for the isolation tester's purposes to use a single element
* buffer and check if the number of safe snapshot blockers is non-zero.
*/
if (GetSafeSnapshotBlockingPids(blocked_pid, &dummy, 1) > 0)
PG_RETURN_BOOL(true);
PG_RETURN_BOOL(false);
}
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