Detection of response time failures of real-time software

Abstract

Classical software reliability research has tended to focus on behavioral-type failures which typically manifest themselves as incorrect or missing outputs. In real-time software, a correct output which is not produced within a specijied response time interval may also constitutes a failure. As a result, response time failures must also be taken into account when real-time software reliability is assessed. Response-time requirements can be stated in a hard or a soft form. The latter form is often preferred when the quality of service offered is of concern. In a number of real-time applications, the responses to a particular stimulus are highly state dependent and, therefore, the response time requirements must be predicated on state.This paper considers the case where the detection of response times failures is done by a separate unit which observes the inputs and outputs of the target software.Automatic detection of such failures is complicated by state dependencies which require the unit to track a target's state as well as the elapsed times between specified stimulus and response pairs. A novel, black-box approach is described for detecting response time failures and quality of service degradations of session-oriented, real-time software.The behavior of the target software is assumed to be specijied in a formalism based on the notion of communicating extended finite state machines. The response time failure detection unit, implemented independently of the target software, interprets a formal model derived directly from the target's requirement specijications. The model is used both to track the state of the target and to determine when to start and stop time interval timing measurements. Measurements of multiple response time intervals may occur simultaneously. The approach was evaluated on the call processing program of a small telephone exchange. Some results of the evaluation are presented and discussed.

Requirements-based monitors for real-time systems

“…2) Temporal properties -the order of events, which can be checked by comparing the sequence of observed events with that specified by either a temporal logic [7], [8]; a finite state machine model [15], [6]; or a context-free grammar [2]. 3) Timing constraints -the time elapsed between events, which can be expressed using a real-time logic [23], [17]; or as extensions on a finite state machine model [25], [34]. This paper contributes to this body of work in two ways: Firstly, it considers all three of these classes of properties, which we have only seen done in one other work [18].…”