Abstract:
A method of generating a heartbeat signal for an application comprising one or more objects that may enter a halt state is described. The method comprises: sending a status request to a defined interface on each object; and monitoring responses to the status requests to ascertain if each object is operating normally or in a halt state. The method further comprises: generating an application valid signal in the event that each object is operating normally; transmitting the application valid signal, if generated, to a monitoring component independent of the application; and generating at the monitoring component a heartbeat valid signal in response to receipt of the application valid signal.

Description:
FIELD OF INVENTION 
     The present invention relates to a heartbeat system. 
     BACKGROUND OF INVENTION 
     During execution, a software object may contain one or more active threads of execution and may access one or more other software objects. A thread of execution within an object may enter a permanently halted state (a hung state) for a number of reasons. These reasons include: a mutually exclusive resource conflict, an external error (such as an event from a device never occurring), and coding logic error (such as an infinite loop). 
     To enable a system to detect when a thread of execution has entered a halted state, software objects are typically coded with logic that generates a heartbeat at defined time intervals, and conveys this heartbeat to a monitoring object. A heartbeat is a signal that is emitted at regular intervals by a software object to demonstrate to another software object (the monitoring object) that it is still running (that is, it is not halted). If the monitoring object does not receive a heartbeat within the defined time then the monitoring object regards the thread of execution as halted. 
     This type of heartbeat system has several disadvantages. For example, the monitoring object must be aware of all of the heartbeats that are present in the system, and the defined time interval for each heartbeat, so that it can ascertain if a heartbeat has been missed. As the number of objects generating a heartbeat increases, the management overhead increases for the monitoring object. Furthermore, every object having a thread of execution that may enter a halt state must have its own code to generate a heartbeat, which is an inefficient use of code. This is also an inefficient use of processing time, since every object automatically produces a regular heartbeat. 
     SUMMARY OF INVENTION 
     Accordingly, the invention generally provides methods, systems, apparatus, and software for an improved heartbeat system. 
     In addition to the Summary of Invention provided above and the subject matter disclosed below in the Detailed Description, the following paragraphs of this section are intended to provide further basis for alternative claim language for possible use during prosecution of this application, if required. If this application is granted, some aspects may relate to claims added during prosecution of this application, other aspects may relate to claims deleted during prosecution, other aspects may relate to subject matter never claimed. Furthermore, the various aspects detailed hereinafter are independent of each other, except where stated otherwise. Any claim corresponding to one aspect should not be construed as incorporating any element or feature of the other aspects unless explicitly stated in that claim. 
     According to a first aspect there is provided a method of generating a heartbeat signal for an application comprising one or more objects that may enter a halt state, the method comprising: 
     (a) sending a status request to a defined interface on each object; 
     (b) monitoring any response to the status requests to ascertain if each object is operating normally or in a halt state; 
     (c) generating an application valid signal in the event that each object is operating normally; 
     (d) transmitting the application valid signal, if generated, to a monitoring component independent of the application; and 
     (e) generating at the monitoring component a heartbeat valid signal in response to receipt of the application valid signal. 
     The step of sending a status request to a defined interface on an object may be implemented using a component within the application. Alternatively, the step of sending a status request to a defined interface on an object may be implemented using a component external to the application. 
     The defined interface may be common to all objects within the application, which has the advantage that status requests only have to conform to one interface. Alternatively, the defined interface may be different for different objects within the application. 
     The step of monitoring any response to the status requests to ascertain if each object is operating normally or in a halt state may include the sub-steps of either (i) receiving a response from each object, or (ii) not receiving a response from every object within a response time. The response from the object may indicate that the object is operating normally (that is, not in a halt state), or in a halt state. The response time may be selected such that a response not being received within the response time indicates that the object is in a halt state. 
     The method may comprise the further step of (c+1) generating an application invalid signal in the event that at least one object is in a halt state. 
     The method may comprise the further step of (d+1) transmitting the application invalid signal, if generated, to the monitoring component. 
     The method may comprise the further step of (f) generating at the monitoring component a heartbeat invalid signal in the event that either (i) the application valid signal is not received within a reporting interval, or (ii) an application invalid signal is received. 
     The method may be repeated after each heartbeat interval has elapsed. 
     Steps (a) and (b) may be repeated every polling interval. 
     The step of transmitting the application valid signal to a monitoring component independent of the application may be repeated once in every reporting interval if the polling interval is longer than the reporting interval. 
     The step of generating at the monitoring component a heartbeat valid signal may be implemented once in every heartbeat interval if the reporting interval is longer than the heartbeat interval. 
     Each object may have a different polling interval. Alternatively, the same polling interval may be applied to each object, or to each object within the same application suite. 
     According to a second aspect there is provided a heartbeat system comprising: 
     (i) an application comprising:
         (a) at least one object that may enter a halt state, each object including a defined interface identical for all objects and for receiving status requests; and   (b) a querying component arranged to ascertain if each object is operating normally or in a halt state by sending a status request to the defined interface of each object, and being further arranged to transmit an application valid signal when all objects are operating normally;       

     (ii) a monitoring component in communication with the querying component and operable to receive the application valid signal therefrom, the monitoring component being arranged to generate (a) a heartbeat valid signal in the event that the application valid signal is received within a reporting interval, or (b) a heartbeat invalid signal in the event that the application valid signal is not received within the reporting interval. 
     The querying component may be further arranged to transmit an application invalid signal when one or more objects are in a halt state. 
     The monitoring component may be arranged to generate (b) a heartbeat invalid signal in the event that the application valid signal is not received within the reporting interval, or the application invalid signal is received. 
     The heartbeat system may comprise a plurality of applications and the monitoring component, each of the plurality of applications including (a) at least one object that may enter a halt state, each object including a defined interface identical for all objects within that application (or across the plurality of applications) and for receiving status requests; and (b) a querying component. Thus, only one monitoring component is required to monitor multiple applications, each of the multiple applications may comprise multiple objects, each of these objects having the same defined interface for receiving and responding to status requests. 
     The querying component may create a communication object arranged to communicate with the monitoring component. The communication object may register with the monitoring component and may provide parameters to the monitoring object. These parameters may include (i) a reporting interval and (ii) a polling interval. The reporting interval is the defined time within which the application valid signal should be communicated from the communication object to the monitoring component. The polling interval is the time period within which (or event trigger in response to which) the querying component must send a status request to the defined interface of each object to ascertain if each object is operating normally or in a halt state. There may be multiple polling intervals because different objects may have different polling intervals. Alternatively, all objects may have the same polling interval. 
     The monitoring component may further comprise a process list object. The process list object may include a list of all processes that are registered with the monitoring component. 
     Where the querying component includes a communication object arranged to communicate with the monitoring component, the querying component may be arranged to register the communication object with the process list object. The querying component may register a process name of the communication object with the process list object. 
     The monitoring component may be further arranged to update an event log to indicate whether a heartbeat valid signal or a heartbeat invalid signal was generated by the monitoring component. 
     The components may be defined in the Microsoft (trade mark).NET framework. The components may communicate using inter-process communication (IPC). 
     As used herein, an “object” refers to a software entity including data and instructions that can be executed. 
     It should now be appreciated that this aspect has the advantage that instead of having to provide a heartbeat function within each object, each object can be provided with a common interface. Each object responds to a status request via this interface. The objects do not have to generate heartbeats, they merely have to respond to requests when they arrive, thereby saving valuable processing time. 
     According to a third aspect there is provided a computer program arranged to implement the steps of the first aspect. 
     The computer program may be tangibly embodied on a record medium, executed on a computer memory, or propagated on a signal carrier. 
     According to a fourth aspect there is provided a self-service terminal programmed to implement the steps of the first aspect. 
     The self-service terminal may be an automated teller machine (ATM), an information kiosk, a financial services centre, a bill payment kiosk, a lottery kiosk, a postal services machine, a check-in and/or check-out terminal such as those used in the retail, hotel, car rental, gaming, healthcare, and airline industries, and the like. 
     According to a fifth aspect there is provided a method of generating a heartbeat from an application comprising one or more objects that may enter a halt state, the method comprising: 
     (a) sending a status request to a defined interface on an object to ascertain if that object is operating normally or in a halt state; 
     (b) receiving a response from the object; 
     (c) repeating steps (a) and (b) for each object; 
     (d) generating an application status signal based on the responses to the status requests; 
     (e) transmitting the application status signal to a monitoring component independent of the application; 
     (f) generating at the monitoring component a heartbeat valid signal in the event that the application status signal (i) is received within a defined time and (ii) indicates that each object is operating normally; 
     (g) generating at the monitoring component a heartbeat invalid signal in the event that either (i) the application status signal is not received within the defined time, or (ii) the application status signal indicates that at least one object is in a halt state. 
     The method may further comprise a method of generating a heartbeat from a plurality of applications, each application comprising one or more objects that may enter a halt state, the method comprising: 
     repeating steps (a) to (e) for each application; and step (f) may further comprise generating at the monitoring component a heartbeat valid signal in the event that an application status signal from each application (i) is received within a defined time and (ii) indicates that each object is operating normally; and step (g) may further comprise generating at the monitoring component a heartbeat invalid signal in the event that either (i) one or more application status signals is not received within the defined time, or (ii) one or more application status signals indicates that at least one object is in a halt state. 
     Although step (c) appears to be sequential to steps (a) and (b), the above language does not exclude step (c) being performed simultaneously with steps (a) and (b)), so that the above language specifically includes the possibility that a status request may be sent simultaneously to all objects whose status is to be ascertained. 
     The step of generating an application status signal based on responses to the status requests may include the sub-step of generating a valid application status signal in the event that no response to the status requests indicates that an object is in a halt state. 
     The step of generating an application status signal based on responses to the status requests may include the sub-step of generating an invalid application status signal in the event that either (i) one or more responses to the status requests indicates that an object is in a halt state, or (ii) one or more responses to the status requests are not received. Alternatively, an application status signal may not be generated if a valid application status signal cannot be generated. 
     The step of transmitting the application status signal to a monitoring component independent of the application may be implemented once in every reporting interval. 
     The step of generating at the monitoring component a heartbeat valid signal may be implemented once in every heartbeat interval provided that the most recently received application status signal (i) was received within a defined time and (ii) indicated that each object was operating normally. 
     The poll interval may be independent of the heartbeat interval. 
     According to a sixth aspect there is provided a computer programmed to implement the steps of the first aspect. 
     Definitions 
     The following time periods used herein are defined below: 
     “Polling Interval”. This refers to the time period during which the querying component must issue a status request to an object. Each object being queried may have its own polling interval, or a uniform polling interval may be used for all objects in the application, or a global polling interval may be used for all objects across multiple applications (if multiple applications are used). 
     “Response Time”. This refers to the time period within which an object must respond to a status request. Failure of an object to respond within the response time may cause the querying component to regard that object as being in a halt state. 
     “Reporting Interval”. This refers to the time period during which an application valid signal must be transmitted to the monitoring component for the monitoring component to generate a heartbeat valid signal. 
     “Heartbeat Interval”. This refers to the time period during which a heartbeat valid signal must be transmitted to a management system (that is, software external to the application(s) that is responsible for monitoring timely receipt of heartbeat valid signals) for the management system to regard the application (or applications, where multiple applications are executing) as operating normally (that is, not in a halt state). 
     For clarity and simplicity of description, not all combinations of elements provided in the aspects recited above have been set forth expressly. Notwithstanding this, the skilled person will directly and unambiguously recognize that unless it is not technically possible, or it is explicitly stated to the contrary, the consistory clauses referring to one aspect are intended to apply mutatis mutandis as optional features of every other aspect to which those consistory clauses could possibly relate. 
     These and other aspects will be apparent from the following specific description, given by way of example, with reference to the accompanying drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a simplified schematic diagram of an SST memory executing software components providing a heartbeat function according to an embodiment of the present invention; 
         FIG. 2  is a simplified sequence diagram illustrating messages and events associated with the software components of  FIG. 1  as they register to provide a heartbeat function; 
         FIG. 3  is a simplified sequence diagram following on from the sequence diagram of  FIG. 2  and illustrating messages and events associated with the software components of  FIG. 1  as they co-operate to provide a heartbeat valid signal to a management system; 
         FIG. 4  is a simplified sequence diagram following on from the sequence diagram of  FIG. 2  and illustrating messages and events associated with the software components of  FIG. 1  as they co-operate to provide a heartbeat invalid signal to a management system; and 
         FIG. 5  is a simplified schematic diagram of an SST memory executing software components providing a heartbeat function according to another embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION 
     Reference is first made to  FIG. 1 , which is a simplified, schematic diagram of software components executing in an SST memory  10  according to one embodiment of the present invention. In this embodiment, the SST memory is an ATM memory. 
     As shown in  FIG. 1 , the memory  10  executes various software entities, including an application suite  12 , a monitoring suite  14 , and a management system  16 . These software entities are implemented using the Microsoft .NET framework. 
     The application suite  12  includes transaction control code  20  comprising a plurality of application business and user interface objects used for collecting information relating to a customer, managing components in the ATM, obtaining authorization from a remote transaction authorization host (not shown), and other conventional functions of an ATM. 
     The application suite  12  also comprises a querying component  24  and a communication object  26  instantiated by the querying component  24 . 
     The transaction control code  20  comprises a large number of objects (labeled “Object  1 ” to “Object n” in  FIG. 1 ), although only three objects  32 , 34 , 36  are illustrated in  FIG. 1 . Each of these objects  32 , 34 , 36  includes an identical, defined interface (referred to herein as the “IActivityMonitor” interface)  38  that supports a single method (the “IsActive” method). It should be appreciated that each of the objects  32 , 34 , 36  includes other interfaces to enable the objects  32 , 34 , 36  to perform their required functions, but these other interfaces are conventional and not required to understand this embodiment, so will not be described in detail herein. 
     This IActivityMonitor interface  38  allows the querying component  24  to send a status request to any object having that interface. If that object is not in a halt state, then it responds to that status request within a predetermined time (referred to herein as the response time) with an indication that the object is operating normally. In this embodiment, the response time is one second, and a response to the status request is provided as a single bit which is active. If the object is in a halt state then it will either not respond within the response time, or will respond with an indication (provided as a single bit which is inactive) that the object is in a halt state. 
     The communication object  26  is an interprocess communication (IPC) remoteable object, and is responsible for enabling the querying component  24  to communicate with the monitoring suite  14 . 
     The querying component  24  includes a timer routine  40  to ensure that the querying component  24  sends a status request to each object  32 , 34 , 36  once every polling interval. In this embodiment, the polling interval is the same for all objects in the application suite  12 , and has a value of sixty seconds. The querying component  24  also uses the timer routine  40  to ensure that the querying component  24  transmits an application valid signal once every reporting interval. In this embodiment the reporting interval is ninety seconds. 
     The monitoring suite  14  comprises a monitoring component  50 , and a process list object (referred to herein as a monitor client list object)  52  instantiated by the monitoring component  50 . The monitor client list object  52  is also an IPC remotable object, and is responsible for maintaining a list of processes within applications (such as the process corresponding to communication object  26  in the application suite  12 ) that are being communicated with. 
     If all of the objects  32 , 34 , 36  in the application suite  12  are operating normally (that is, not in a halt state), then the monitoring component  50  receives an application valid signal from communication object  26  once in every reporting interval (ninety seconds in this embodiment). The monitoring component  50  uses this application valid signal to generate a heartbeat valid signal. The monitoring component  50  then transmits the heartbeat valid signal to a heartbeat monitor  60  within the management system  16 , and writes a heartbeat valid entry to an event log  62  within the management system  16 . 
     If one or more of the objects  32 , 34 , 36  in the application suite  12  are not operating normally (that is, in a halt state), then the monitoring component  50  does not receive an application valid signal from communication object  26 . The monitoring component  50  responds to the absence of the application valid signal to generate a heartbeat invalid signal. The monitoring component  50  then transmits the heartbeat invalid signal to the heartbeat monitor  60 , and writes a heartbeat invalid entry to the event log  62 . 
     The monitoring component  50  includes a timer routine  54  to ensure that a heartbeat signal (either heartbeat valid or heartbeat invalid) is transmitted to the heartbeat monitor  60  once in every heartbeat interval, which is one hundred and twenty seconds in this embodiment. 
     The operation of the software entities of  FIG. 1  will now be described with reference to  FIG. 2 , which is a simplified sequence diagram illustrating messages and events associated with the application suite  12  and the monitoring suite  14 , when the application suite  12  registers to provide a heartbeat function. 
     Initially, the monitoring component  50  is instantiated (event  70  in  FIG. 2 ) prior to any of the processes or components that it monitors. The monitoring component  50  then creates and registers an instance of the monitor client list object  52  (event  72 ). 
     The application suite  12  then starts up and instantiates the querying component  24  (event  74 ). The querying component  24  then registers an instance of the communication object  26  (event  76 ). 
     Using IPC remoting, the querying component  24  then calls the monitor client list object  52  (using the “GetObject” command) to obtain an object reference for the monitor client list object  52  (event  78 ). The querying component  24  is programmed with a name and port of the monitor client list object  52  so that the querying component  24  knows how to access the monitor client list object  52 . 
     Once the querying component  24  has the object reference for the monitor client list object  52 , the querying component  24  can register the process name of the communication object  26  with the monitor client list object  52  (event  80 ). 
     Once the communication object  26  has been registered with the monitor client list object  52 , the monitor client list object  52  updates the monitoring component  50  to inform the monitoring component  50  about the process name of the communication object  26  (event  82 ). 
     The monitoring component  50  uses this process name to obtain an object reference for the communication object  26  (using the “GetObject” command) (event  84 ) and parameters associated with the application suite  12 . These parameters include the reporting interval and the polling interval. 
     At this point, the application suite  12  and the monitoring suite  14  are fully instantiated and set-up for monitoring the status of the objects  32 , 34 , 36  within the application suite  12 . 
     If a new application is added, then this new application would perform similar events (event  74  through event  80 ) to those described above, and the monitoring suite  14  would perform events  82  and  84 , so that the new application would be automatically added as an application to be monitored by the monitoring suite  14 . 
     Reference will now be made to  FIG. 3 , which is a sequence diagram following on from the sequence diagram of  FIG. 2  and illustrating messages and events associated with the application suite  12  and the monitoring suite  14  co-operating to provide a heartbeat valid signal to a management system  16 . 
     The querying component  24  uses its timer routine  40  to measure the polling interval (event  90 ). The querying component  24  ensures that during this polling interval it sends a status request message to all objects  32 , 34 , 36  having the IActivityMonitor interface  38  (event  92 ). 
     When each object  32 , 34 , 36  having the IActivityMonitor interface  38  is instantiated, it registers with a registration list object (not shown). Once all of the objects  32 , 24 , 36  are instantiated, this registration list object (not shown) contains a list of all objects that are to receive status request messages from the querying component  24 . Once the querying component  24  is instantiated, it gets a list of the registered objects (objects  32 , 34 , 36  in this embodiment) from the registration list object (not shown). This enables the querying component  24  to know which objects have the IActivityMonitor interface  38 . 
     The status request message comprises a method (the “IsActive” method) that must be processed by the object  32 , 34 , 36  within the response time (one second in this embodiment). 
     In the example of  FIG. 3 , all of the objects respond with an active bit (indicating that none of the objects is in a halt state). This response generates an “Alive” event (event  94 ) at the querying component  24 , which is used by the communication object  26  to generate and transmit an application valid signal (event  96 ) to the monitoring component  50 . 
     The monitoring component  50  uses its timer routine  54  to measure the heartbeat interval (event  98 ). The monitoring component  50  uses the timer routine  54  to ensure that a heartbeat signal is transmitted to the management system  16  (specifically the heartbeat monitor  60 ) in a timely manner, that is, once during each heartbeat interval (one hundred and twenty seconds in this embodiment). 
     In this example, an application valid signal was received from the communication object  26 , so the monitoring component  50  creates and transmits a heartbeat valid signal (event  100 ) to the management system  16 . 
     The monitoring component  50  also writes a heartbeat event to the event log  62 , indicating that a heartbeat valid signal was generated. As is known to those of skill in the art, the event log  62  is used as an aid in identifying any causes of failure caused by the software entities because it contains a list of events triggered by instrumented code. 
     Reference will now be made to  FIG. 4 , which is a sequence diagram following on from the sequence diagram of  FIG. 2  and illustrating messages and events associated with the application suite  12  and the monitoring suite  14  co-operating to provide a heartbeat invalid signal to a management system  16 . 
     In the same manner as for  FIG. 3 , the querying component  24  uses its timer routine  40  to measure the polling interval (event  102 ). The querying component  24  ensures that during this polling interval it sends a status request message to all objects  32 , 34 , 36  having the IActivityMonitor interface  38  (event  104 ). 
     The status request message comprises the IsActive method, which must be processed by the object  32 , 34 , 36  within the response time (one second in this embodiment). 
     In the example of  FIG. 4 , at least one of the objects  32 , 34 , 36  does not respond within the response time. The querying component  24  interprets this lack of response as meaning that one of the objects  32 , 34 , 36  is in a halt state. As a result, no “Alive” event is generated at the querying component  24 , so an application valid signal is not sent from the communication object  26  to the monitoring component  50 . 
     The monitoring component  50  uses its timer routine  54  to measure the heartbeat interval (event  106 ). After the heartbeat interval has elapsed, since an application valid signal was not received from the communication object  26  within the heartbeat interval, the monitoring component  50  creates and transmits a heartbeat invalid signal (event  108 ) to the heartbeat monitor  60 . 
     The monitoring component  50  also writes a heartbeat ceased event to the event log  62 , indicating that a heartbeat invalid signal was generated. 
     Reference will now be made to  FIG. 5 , which is a simplified schematic diagram of an SST memory  200  executing software components providing a heartbeat function according to another embodiment of the present invention. 
     As shown in  FIG. 5 , the memory  200  executes various software entities, including the application suite  12 , the monitoring suite  14 , the management system  16  (all of the preceding software entities being identical to the corresponding entities of  FIG. 1 ), and a supervisor application suite  212 . All of these software entities execute within a .NET framework. 
     The supervisor application suite  212  includes supervisor control code  220  comprising a plurality of objects used for assisting a service person in conducting maintenance, settlement, upgrading, and diagnostic functions. 
     The supervisor application suite  212  also comprises a querying component  224  and a communication object  226  instantiated by the querying component  224 . Querying component  224  and communication object  226  are very similar, and provide corresponding functions, to querying component  24  and communication object  26 . However, querying component  224  may have a different response time and a different polling time, if desired. The querying component also includes a timer routine  240 . 
     The supervisor control code  220  comprises a large number of objects (labeled “Object  1 ” to “Object m” in  FIG. 5 ), although only three objects  232 , 234 , 236  are illustrated in  FIG. 5 . Each of these objects  232 , 234 , 236  includes an identical defined interface (the “IActivityMonitor” interface)  38  that supports a single method (the “IsActive” method). It should be appreciated that each of the objects  232 , 234 , 236  includes other interfaces to enable the objects  232 , 234 , 236  to perform their required functions, but these other interfaces are conventional, so will not be described in detail herein. 
     In a similar manner to the first embodiment ( FIGS. 1 to 4 ), once the monitoring component  50  is instantiated and has created and registered an instance of the monitor client list object  52 , both the application suite querying component  24  and the supervisor suite querying component  224  register with the monitoring component  50  and create communication objects  26 , 226  respectively. 
     The application suite querying component  24  and the supervisor suite querying component  224  operate independently of each other, sending status messages to their respective objects within their respective polling intervals. 
     Only if the monitoring component  50  receives a heartbeat valid signal from each of the application suite  12  and the supervisor suite  212  will the monitoring component  50  generate and transmit a heartbeat valid signal to the heartbeat monitor  60 . If either the application suite  12  or the supervisor suite  212  does not provide an application valid signal, then the monitoring component  50  will generate and transmit a heartbeat invalid signal to the heartbeat monitor  60 . the monitoring component  50  may also update the event log  62  with details of which application suite ( 12  or  212 ) did transmit an application valid signal, and which application suite ( 12  or  212 ) did not transmit an application valid signal. 
     It should now be appreciated that these embodiments have the advantage of providing a simple interface for objects that may enter a halt state, thereby avoiding having to code a heartbeat generation routine into every object. Each object can be individually coded as to how to respond to a status request most efficiently. A single monitoring suite is provided to record responses from different applications, and to provide a single signal from which a heartbeat can be generated. 
     Various modifications may be made to the above described embodiments within the scope of the invention, for example, in other embodiments, a different software architecture may be provided that does not use the Microsoft .NET framework. 
     In other embodiments, an object in a halt state may be able to respond to a status request with an inactive bit (indicating that at least one of the objects is in a halt state). In such embodiments, this response may generate a “NotAlive” event at the querying component, which may be used by the communication object to generate and transmit an application invalid signal to the monitoring component. Alternatively, the communication object may not generate any signal, and the absence of an application valid signal may be used by the monitoring component to generate and transmit a heartbeat invalid signal. 
     In other embodiments, instead of the absence of an application valid signal being used to trigger a heartbeat invalid signal, the communication object may generate and transmit a heartbeat invalid signal, which can be used to trigger a heartbeat invalid signal. 
     In other embodiments, a more complex defined interface  38  may be provided than described in the above embodiments. For example, the interface may allow for more details about the thread that was not executing, or any underlying problem causing the thread to halt. 
     In other embodiments, the value of the time (the response time) and intervals (polling interval, reporting interval, and heartbeat interval) may be different to those provided above. 
     In other embodiments, the polling interval may be triggered by an event rather than the elapse of time. 
     In other embodiments, the heartbeat system may be used on a computing device other than a self-service terminal. 
     In other embodiments, the heartbeat system may be used on a self-service terminal other than an ATM. 
     In other embodiments, the querying component  24  may be programmed with a list of objects that support the defined interface  38 . 
     The steps of the methods described herein may be carried out in any suitable order, or simultaneously where appropriate. The methods described herein may be performed by software in machine readable form on a tangible storage medium or as a propagating signal. 
     The terms “comprising”, “including”, “incorporating”, and “having” are used herein to recite an open-ended list of one or more elements or steps, not a closed list. When such terms are used, those elements or steps recited in the list are not exclusive of other elements or steps that may be added to the list. 
     Unless otherwise indicated by the context, the terms “a” and “an” are used herein to denote at least one of the elements, integers, steps, features, operations, or components mentioned thereafter, but do not exclude additional elements, integers, steps, features, operations, or components.