/*-------------------------------------------------------------------------
 *
 * 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/builtins.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);
}
