1 files changed, 96 insertions, 0 deletions
diff --git a/src/backend/utils/adt/waitfuncs.c b/src/backend/utils/adt/waitfuncs.c
new file mode 100644
index 00000000000..d9c92c3eee7
--- /dev/null
+++ b/src/backend/utils/adt/waitfuncs.c
@@ -0,0 +1,96 @@
+/*-------------------------------------------------------------------------
+ *
+ * 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 "utils/array.h"
+#include "utils/builtins.h"
+
+
+/*
+ * 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
+ * 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);
+	ArrayType  *blocking_pids_a;
+	int32	   *interesting_pids;
+	int32	   *blocking_pids;
+	int			num_interesting_pids;
+	int			num_blocking_pids;
+	int			dummy;
+	int			i,
+				j;
+
+	/* 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);
+}