+/**
+ * Iterate through two lists at once. Stops at the end of the shorter list.
+ *
+ * This is safe against either current node being removed or replaced.
+ */
+#define foreach_two_lists(__node1, __list1, __node2, __list2) \
+ for (exec_node * __node1 = (__list1)->head, \
+ * __node2 = (__list2)->head, \
+ * __next1 = __node1->next, \
+ * __next2 = __node2->next \
+ ; __next1 != NULL && __next2 != NULL \
+ ; __node1 = __next1, \
+ __node2 = __next2, \
+ __next1 = __next1->next, \
+ __next2 = __next2->next)
+