Abstract:
A computer system includes a main processor and a supervisory processor. The main processor provides status signals when a fault condition exists and responds to control signals for fault recovery. The supervisory processor instantiates objects from a fault class in response to the status signals. Objects are polymorphic in that each object has substantially the same methods available at its interface though each object corresponds to a different fault. Methods accomplish fault recovery by providing the control signals. System operation exhibits fewer errors by the supervisory processor and system expansion is more easily accommodated with greater reuse of proven program code than possible with prior supervisory processor software.

Description:
FIELD OF THE INVENTION 
     This invention relates to systems having fault monitors and to automated methods for responding to faults. 
     BACKGROUND OF THE INVENTION 
     In many systems, unexpected system operation can be detected by circuits generally known as fault monitor circuits. Fault monitoring is accomplished in a conventional computer system, for example, by a combination of such circuits and fault processing software. Fault processing software records the fact of fault detection by the circuits in order that the event giving rise to the fault can be subsequently analyzed and the circumstances causing it can be treated. By treating the event, continued operation of the system is assured with minimum disruption, notice of intermittent operations can guide maintenance activity, and the overall cost of ownership of the system can be reduced while obtaining, to the greatest extent possible, uninterrupted system operation. 
     Due to the difficulty of analyzing system operations, the required reliability of fault processing software is extremely high. High reliability software is conventionally obtained through exhaustive software testing. However, in large systems, the difficulty of anticipating sophisticated fault events increases the number of test suites, the cost of developing test suites, and the cost of performing software testing using the test suites. 
     In view of the problems described above and related problems that consequently become apparent to those skilled in the applicable arts, the need remains in systems having fault monitors for economical and reliable automated methods for responding to faults. 
     SUMMARY OF THE INVENTION 
     Accordingly, a system in one embodiment of the present invention includes a central processor and a service processor. The central processor includes a plurality of sets of equivalent processing units, a set of the plurality being capable of providing a fault signal for a failing unit. The service processor responds to the fault signal by performing a method which includes (a) instantiating a polymorphic fault object; (b) identifying the failing unit; and (c) executing a method of the polymorphic fault object to limit use of the failing unit. 
     According to a first aspect of such a system, fault processing software includes fault objects in hierarchical relationship. The hierarchical relationship permits evolution of the software according to techniques that minimize the scope of software revision. Tests of portions of the software outside the scope of revision need not be repeated, thus avoiding the costs and delays conventionally associated with software testing. 
     A prerecorded data storage medium in one embodiment of the present invention includes a data storage medium and indicia recorded on the medium. The indicia include instructions, in a program for a first computer, for: (a) recognizing a fault signal provided by a fault monitor of a second computer; (b) instantiating a fault object in response to the fault signal, the fault object comprising a data structure that identifies a fault processing method; and (c) dynamically binding the fault processing method to the program, in response to the data structure. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     A preferred exemplary embodiment of the present invention is described below with reference to the drawing in which: 
     FIG. 1 is a block diagram of a computer system in one embodiment of the present invention; 
     FIG. 2 is a hierarchy diagram of derived classes according to one embodiment of the present invention; 
     FIG. 3 is an exemplary run-time map of memory utilization during fault processing according to the present invention; 
     FIG. 4 is a data flow diagram for a fault processing method in one embodiment of the present invention. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     FIG. 1 illustrates a system for the purpose of describing various aspects of the present invention, including fault processing with polymorphic fault objects. A system of the present invention is any electromechanical system having fault monitoring capability. For example, computer system 100 includes central processor 110 and service processor 170. Service processor 170 cooperates with central processor 110 to perform fault processing for faults occurring within central processor 110. 
     Central processor 110 is any conventional general purpose computer of the type having several sets of modular computing equipment. In a first set, from one to four substantially identical central processing unit modules (CPU) 151-154 cooperate by communication via system bus 112. In a second set, from one to four substantially identical input/output unit modules (IOU) 121-124 cooperate by communication via system bus 112. Each IOU services a respective member of a third set of input/output subsystem modules (IOSS) 131-134. Members of the third set provide a variety of different system functions with redundancy according to system requirements. For example, one or more IOSSs provide data storage and retrieval, printing, telecommunications, transactional I/O, user terminal I/O, or similar conventional input/output services. In a fourth set, from one to eight substantially identical memory unit modules (MU) 141-148 cooperate by communication via memory bus 113. 
     A system control unit (SCU) 111 governs system organization. A clock and maintenance unit (CMU) 114 governs system operation, fault monitoring, and recovery. A member of a set (CMU, MU, IOU, or IOSS) is enabled (or disabled) by CMU 114 by supplying (or removing) clocks, power, and gating signals 116 provided to all units by CMU 114. Each unit (CPU, MU, IOU, IOSS, SCU, or CMU) includes a fault monitoring circuit that provides fault signals 117 on the occurrence of any abnormal condition (for example excessive noise, any hardware failure, any out of range analog parameter, any out-of-bounds digital value, or any invalid operation in microcode, firmware, or software). CMU 114 responds to fault signals 117 and reports the identification of the unit on which the abnormal condition occurred and the type of abnormal condition by providing fault signals on bus 115 to service processor 170. 
     A service processor is any programmable computer that responds to fault signals with commands that enable or limit operation of any unit of a monitored system. For example, central processor 110 employs fault monitoring circuits as described above which communicate over bus 115 to service processor 170 and service processor 170 provides command signals over bus 115 to affect changes in system operation and fault monitoring by CMU 114. 
     Service processor 170 includes conventional input/output circuits 174 coupled by a conventional bus (not shown) to conventional central processing unit (CPU) 172. Input/output circuits may include a conventional monitor and keyboard for operator interaction with the service processor. Service processor 170 performs instructions of fault processor program 180, not shown, provided to CPU 172 by file system 176. 
     File system 176 is any conventional data storage device, separate or integral with CPU 172. For example, when service processor 170 is a personal computer, file system 176 includes a disk drive with removable media for receiving the program, and a disk drive with nonremovable media for fast access to the program. Such media include indicia of instructions of fault processor 180 of the present invention. 
     A program of the present invention is any firmware or software arranged to perform fault processing by polymorphic fault objects. For example, FIGS. 2 through 4 describe fault processor 180 performed by service processor 170. 
     Fault processor 180 utilizes, in some aspects, principles of object-oriented programming. Concepts and terminology used to describe fault processor 180 are intended to be consistent with current research, industry standards, and the conventions of the current major manufacturers and developers of computer systems and software. Guidance into the extensive literature that applies to the present invention is provided by: &#34;Object-Oriented Languages, Systems and Applications,&#34; edited by Gordon Blair, et al., Halsted Press of New York N.Y., 1991; and &#34;The Java Handbook,&#34; by Patrick Naughton, Osborne McGraw-Hill of Berkley Calif., 1996; &#34;C++ The Complete Reference,&#34; by Herbert Schmildt, Osborne McGraw-Hill of Berkley Calif., 1995; and the bibliographic references therein. 
     An object oriented run-time environment is any software environment supporting run-time polymorphism, including, for example, environments characterized by direct execution and environments characterized by interpretation. Fault processor 180 in one variation is interpreted, for example, as would be the case when developed in Smalltalk or Java programming languages and interpreted by a virtual machine. In another variation, fault processor 180 is executed directly, for example, as would be the case when developed in C++ or Pascal programming languages, compiled, linked, and loaded for execution with object oriented run-time supporting routines. In the former case, the object oriented run-time environment includes a Smalltalk processor or a virtual machine implemented in hardware or software. In the latter case, the object oriented run-time environment includes linked library routines. 
     Run-time polymorphism is accomplished in any conventional run-time environment having dynamic binding. Whereas static type checking and static binding are accomplished during compile-time, reassignment of data types and dynamic binding are accomplished during run-time. 
     Run-time polymorphism may be better understood in light of the following brief overview of object-oriented programming concepts, including classes, objects, interfaces, and polymorphism. A class is any template used to define one or more objects. A class is defined using the syntax of an object oriented programming language (source code) and specifies at least three types of components: variables, methods that operate on variables, and interfaces. 
     Fault classes are conventionally defined in a hierarchy, as shown for example in hierarchy diagram 200 for fault processor 180 in FIG. 2. Fault class CFault 210 specifies variables, methods, and interfaces common to all fault objects in fault processor 180. Classes CFaultCSS 220 and CFaultIOSS 230 distinguish computing subsystem fault processing from input/output subsystem fault processing and provide variables, methods, and interfaces common only to each respective subsystem. Additional fault classes 222-228 and 232-234 provide variables, methods, and interfaces particular to fault processing for similarly named functional units of computer system 100. 
     A fault object is any instance of a fault class from which it was defined. As illustrated in the exemplary run-time memory map of FIG. 3, fault objects 352-356 come into existence by instantiation during run-time. Instantiation involves allocation and initialization of data memory 304 for the storage of variables and pointers for each fault object. Pointers identify entry points 336, 338, 348 in program memory for appropriate methods, i.e. operations on the variables. The specification of an object (class source code) defines immutable aspects of data members and member functions for fault objects in the fault class. The instantiation of a fault object, on the other hand, includes instance variables for the changing values and attributes of data members and (variable) pointers to entry points for the member functions. The compiler, interpreter, or virtual machine constructs one or more conventional data structures for convenient access to objects and their members. 
     The run-time map of FIG. 3 illustrates memory utilization during run-time fault processing according to fault processor 180. At the instant in time shown, program memory 302 includes instructions for main program 310 and constants and instructions for class CFault. For clarity of presentation, only those constants and instructions for derived classes CFaultCPU 311 and CFaultIOU 312 are shown. Data memory 304 includes three fault objects 352, 354, 356 instantiated in response to fault signals received by service processor 170 from CMU 114. Each fault object 352, 354, and 356 is instantiated according to the fault determined and reported by CMU 114. A fault class template may be used to instantiate several objects and each fault object will include its individual instance variables and its individual pointer values. 
     Any association of a particular method with an object is called binding. Binding, when accomplished at least in part at run-time is called dynamic binding. For example, an indirect call through a virtual function table accomplishes dynamic binding as set forth in the proposed ANSI standard C++ programming language. 
     A fault class defines a method by defining a specification 332, 342 for the method and an implementation 334, 344 for the method. The specification includes a name for the method, the names and types of its arguments, the type of its return value (if any), and provisions for exceptional conditions which may arise when the method is performed (such as overflow, etc.). The implementation of a method (e.g. executable code) has one or more entry points, i.e. memory addresses from which execution will commence. When the specification is not accompanied by an implementation, the method is called a virtual function. 
     An interface is any class having conventional member functions without corresponding implementations. Objects defined in classes that derive from an interface cooperate at run-time via pointers collectively called a virtual function table. In some run-time environments, a virtual function table is one of the data structures that is allocated when an object is instantiated. A virtual function table includes pointer variables for entry point values determined at run-time, pointer constants when offsets to entry points can be predicted at compile-time, or a combination of variables and constants. 
     When execution of a program reaches a particular call to a function, an object having the function is instantiated with allocations and values from the hierarchy of classes from which that object was defined. The instantiation proceeds with reference to the signature of the function, which includes the name of the function, the parameter values to be passed, the parameter types, and the expected return value type. One process of dynamic binding (which accompanies instantiation), at least in concept, involves comparing the signature of the method in turn to methods known privately by the object, methods known within the class in which the object is defined, and methods of parent classes in the hierarchy. The pointer identifying the appropriate method for this particular instantiation of the object is associated (dynamically bound) with an entry point of the first method having a specification compatible with the signature. Such a pointer value is stored, for example, in a virtual function table of the object. Another process of dynamic binding involves determining an entry point value for a pointer with reference to pointer values in a virtual function table. 
     A fault class facilitates polymorphism by facilitating method overloading, method overriding, and method inheriting. When a class specifies methods of the same name but with varying argument types, the method name is said to be overloaded. When a derived class specifies a method of the same signature as the parent, the method implementation in the derived class overrides the parent implementation. When a derived class omits the implementation of a method and thereby relies on the implementation of a method in a parent class, the parent class implementation is said to be inherited by the derived class. 
     A polymorphic fault object is any object having a polymorphic member function. A polymorphic function is a function exhibiting method overloading, method overriding, or method inheritance. When classes are derived from an interface, objects in the derived classes ordinarily have polymorphic member functions. 
     The exemplary memory map of FIG. 3 provides an illustration of a conventional process of dynamic binding as further applied to polymorphic fault objects. At instruction 314 of main program 310, a step of the system shut down process is to be performed. In that step, a report of the unique register contents (i.e. a memory dump) for each failing unit is to be produced. Because the details of such a report vary with the type of unit, separate methods are appropriate. However, the report function is needed for all fault objects and so is defined as part of an interface of class CFault. Each derived class or a derived class thereunder contains an implementation for the report function named DumpHardware. Consequently, each polymorphic fault object 352-356 has a virtual function table data structure in data memory 304. 
     Instruction 314 is part of a loop that is performed once for each fault object. Instruction 314 is performed three times with three unique consequences. A conventional linked list, or similar structure (not shown) identifies fault objects 352-356 for processing. In the first performance, a fault object 352 is passed as a parameter to be reported according to the interface. Prior to transferring program control to the appropriate method, the dynamic binding process of the run-time environment is called. During dynamic binding, the signature portion of fault object 352 is compared to the specification portion 332 of fault class CFaultCPU 311, as indicated by relations 326 and 327. Specification portion 332 includes the specifications for base fault classes CFaultCSS and CFault (not shown). The specification of each method having the name DumpHardware is considered until a match is found. Consequently, a pointer to entry point 336 is assigned in object 352. Thereafter, program control transfers on the basis of the pointer value from instruction 314 to entry point 336 on flow path 316 and returns to the instruction following instruction 314 on flow path 317. 
     In the second performance of instruction 314, fault object 354 is passed as a parameter to be reported according to the CFault interface. Prior to transferring program control to the appropriate method, the dynamic binding process of the run-time environment is called. During dynamic binding, the signature portion of fault object 354 is compared to the specification portion 342 of fault class CFaultIOU 312, as indicated by relations 328 and 329. Specification portion 342 includes the specifications for base fault classes CFaultIOSS and CFault (not shown). The specification of each method having the name DumpHardware is considered until a match is found. Consequently, a pointer to entry point 348 is assigned in object 354. Thereafter, program control transfers on the basis of the pointer value from instruction 314 to entry point 348 on flow path 318 and returns to the instruction following instruction 314 on flow path 319. 
     In the third performance of instruction 314, fault object 356 is passed as a parameter to be reported according to the CFault interface. For the sake of example, assume that the argument types of the signature of fault object 356 differ from the signature of fault object 352. Prior to transferring program control to the appropriate method, the dynamic binding process of the run-time environment is called. During dynamic binding, the signature portion of fault object 356 is compared to the specification portion 332 of fault class CFaultCSS 311, as indicated by relations 330 and 331. Specification portion 332 includes the specifications for base fault classes CFaultCSS and CFault (not shown). The specification of each method having the name DumpHardware is considered until a match is found. Consequently, a pointer to entry point 338 is assigned in object 356. Thereafter, program control transfers on the basis of the pointer value from instruction 314 to entry point 338 on flow path 320 and returns to the instruction following instruction 314 on flow path 321. 
     Dynamic binding of fault objects 352 and 356 illustrates a result of method overloading in class CFaultCPU. Different entry points are dynamically bound because the passed parameter in object 352 is of a different type than the passed parameter in object 356. In an alternate organization of fault processor 180, all report functions are overloaded in the same class and the passed parameter operates to identify the appropriate routine through dynamic binding. 
     In a preferred implementation of fault processor 180, the overhead of signature comparison is avoided by calculating the appropriate entry point value using values from a virtual function table that is initialized upon instantiation of the calling object. 
     Dynamic binding of fault object 354 illustrates several ways to reduce the cost of maintaining fault processor 180 as it evolves. Fault processor 180 is expected to evolve to incorporate support for additional fault signals from known unit types and for support for new unit types. If, for example, fault object 354 was of a type not accommodated in a prior release of fault processor 180 and class CFaultIOU was, therefore, absent from that release, then addition of support for an IOU unit type merely involved the definition of a fault class without change to instruction 314 of main program 310 or to existing fault classes CFault 311 or CFaultCSS, not shown. 
     In general, to accommodate additional fault signals, one or more of several approaches may be used: (a) expand an existing fault class which already supports a very similar specification; (b) define a derived fault class and inherit or override functions for the interface; or (c) define a new fault class with the same interface as CFault and either prepare new functions or invoke behavior sharing either with ad hoc references to functions of other classes or with conventional containment and aggregation techniques. In each of these approaches main program instructions such as instruction 314 and implementations 334 and 344 for existing classes are outside the scope of change. The reliability of existing fault processing capabilities is not compromised by the scope of change. Because the scope of testing the revised fault processor is limited to the scope of change, costs for testing are also reduced. 
     Fault processing according to the present invention is accomplished by any number of processing threads on any number of platforms. For example, fault processor 180, in one variation, is performed as a single thread process by a single CPU 172 of service processor 170. In an alternate variation (not shown), fault processing responsibilities including recording the fact of fault detection, analyzing the event giving rise to the fault, and treating the condition are divided or redundantly performed on one or more platforms according to the present invention and conventional multitasking, multi-platform programming techniques. 
     The data flow diagram of FIG. 4 describes a fault processing method 400 without reference (or limitation) to the number of threads, the number of platforms, or the extent of parallel processing used for a particular implementation. In the diagram, process steps (i.e. independent possibly parallel tasks) are illustrated in ovals. Arrows indicate data produced in the performance of each step. In the following description, reference is made, for clarity of presentation, to fault processor 180 operating as part of system 100. 
     The data and procedures used to perform method 400 include any programming language with polymorphism and suitable data structures for entry points. For example, an illustrative embodiment of the &#34;RFH&#34; program in the C++ programming language is described in the Appendix. Material in the Appendix was selected and organized to facilitate description below rather than meet the rigorous specifications of a particular compiler and development environment. 
     In the &#34;Type Definitions&#34; section of the Appendix, several types for data structures are defined. A REV, as identified in the MSG structure type definition, is a &#34;Report of Event&#34; (fault --  report in FIG. 4). An MSG structure is a conventional message structure for queuing messages in an operating system such as the Windows™ operating system marketed by Microsoft, Redmond Wash. 
     Structure type T --  BASICRFHRECORD defines the parameter type used generally for a parameter passed to a polymorphic fault object. The data type CFault* (fault --  id in FIG. 4) is a pointer to a polymorphic fault object. Pointer pNext links fault object instances of the type CFault together (fault --  chain in FIG. 4). 
     Structure type T --  RFHGLOBAL includes operating conditions for RFH. RFH receives control (is instantiated and begins processing) on the occurrence of any fault --  report. RFH continues in control to collect additional fault --  reports that occur close in time to the first fault reported. RFH (expert) provides more accurate recovery actions based on a group of fault --  reports than possible on the basis of isolated individual fault --  reports. 
     Structure type T --  RFHEQUATIONS defines the array element type used in struc --  RFHEQTb1[D --  RFHEQTBLSZ] (fault equation table 416 ). This table is of the type described in U.S. Pat. No. 5,220,662 to Lipton. 
     Structure type T --  RFHL2TBLENTRY defines the array element type used in struc --  RFHL2Tb1[D --  RFHL2TBLSZ] (fault recovery table 419 ). Each array element associates a pointer to a particular recovery procedure with a type of fault. All procedures pointed to in this table conform to the interface defined in class CFault. By dynamic binding, an appropriate method of a polymorphic fault object is executed when transfer of control is made through a pointer in this table. 
     Structure type T --  ORUOBJECTS defines an element for a linked list of optimal replaceable units. In the event that a fault recovery process will involve more than one unit, the plurality of units is identified in a linked list for further processing. 
     In the &#34;Data Items&#34; section of the Appendix, declarations and initializations are illustrated. Fault queue 414 is shown of the type COblist, a class of the type having conventional queue processing member functions such as the COblist class defined in Microsoft Foundation Classes (MFC) marketed by Microsoft. Fault queue 414 is any circular list having a head and a tail. Items are removed from the head and, if desired, are returned to the tail. Items are removable from the middle of the queue, as well. 
     Fault equation table 416 is initialized with faults sufficient for clearly teaching the practice of the invention. A fault handling processor similar to RFH for all types of faults that might occur on system 100 would include perhaps over 100 fault equations utilizing perhaps over 50 fault types. 
     Fault recovery table 419 is initialized with pointers to two recovery procedures, consistent with fault equation table 416. A fault handling processor similar to RFH for all types of faults that might occur on system 100 would be initialized with pointers to one or more fault recovery procedures for each fault equation. 
     In the &#34;Classes and Interfaces&#34; section of the Appendix, classes corresponding to classes 210, 220, 226, and 228 in FIG. 2 are defined. One or more constructors for each class are declared in the body of the class definition. In class CFault 210, a list of virtual functions define an interface to which derived classes 220, 226, and 228 conform. Note that the implementation in CFaultCSS 220 of GotoSystemDisaster() is inherited by objects of the class CFaultCPU 228. Note, also that all members of class CFaultCSS 220 have a commonly named polymorphic member function, ReleaseUnit(). Being commonly named provides a mechanism for dynamic binding. At run-time, unique release operations are performed for each different unit of the computing subsystem (CSS), including CPU, IOU, MU, and SCU units as in FIG. 1, when control is transferred via dynamic binding to an appropriate ReleaseUnit member function. 
     Class CBRFHWindow illustrates support for program evolution. The original class CBodyXMSWindow is derived from a conventional graphical user interface class such as the MFC CFrameWnd class provided by Microsoft. Additional methods are added in the class definition shown in the Appendix to provide further operations for fault processing. 
     In the &#34;Member Functions&#34; section of the Appendix, a skeleton set of member functions is defined in an order selected for clarity of presentation. Where a function is not defined in detail, conventional implementations of the operations implied by the name of the function are intended. Functions having names prefixed with &#34;LXSYS --  &#34; implement the operations of similarly named functions of the type provided by Microsoft in the Windows™ operating system. The variation from the standard Windows function employs conventional event driven software techniques suitably made to comply with the conventional hardware of service processor 170 and bus 115. 
     The description of method 400, below, describes operations at a time after an arbitrary portion of system 100 has generated a fault signal. This introductory fault signal has occurred after a period of time wherein no fault signals were being processed. In response to this introductory fault signal, RFH has been instantiated and is actively executing, though the introductory fault is held for processing. The contents of the memory portion of CPU 172 contains data structures with the values as described above. 
     At step 410, an event driven service routine continues to monitor input/output circuits 174 for receipt of additional fault signals from bus 115. For example in the Appendix, the function CBRFHWindow::ProcessFault has called the function CBRFHWindow::PollEvents which is executing the call to function Wait(P --  wCollectionTime). 
     The fault signals received by input/output circuits 174 are provided in any convenient form to CPU 172. On receipt, structures of the type MSG are enqueued. The function LXSYS --  PeekThisMessage executes on lapse of the collection time and assigns a pointer (&amp;msg) to a structure of the type MSG as it is removed from the message queue. 
     At step 412, received fault reports are used to create polymorphic fault objects. Fault objects are defined in the CFault class hierarchy discussed with reference to FIG. 2, above. According to the example in the Appendix, function LXSYS --  GetAtomIndex determines field wEventID according to the unit reporting the failure. Then, an appropriate constructor in MakeFaultObject copies values from the region of memory identified by handle P --  msg.lparam (also known as the REV or fault --  report) to a region of memory of the type T --  BASICRFHRECORD named strucFltRecord. In this example, we assume that the introductory fault and one or more additional faults were originated by CPU 154 of FIG. 1. The wEventID field of strucFltRecord identifies the CSS as the originator of the fault signal. Further identification of the fault signals is performed by function BRFH --  AnalyzeCSSFault based on fields cbClass and cbSubclass. On review of the field iObjectType assigned by BRFH --  AnalyzeCSSFault, MakeFltObject performs the appropriate constructor using the keyword &#34;new&#34;. A reference to each fault object is then placed in fault queue 414. 
     Fault queue 414 is any data structure providing temporal buffering so that fault recovery can be based on faults that occur close in time. Buffering provides the opportunity to analyze sequential and repeated faults to better assess an approach to recovery from the abnormal condition. 
     At step 418, fault objects consistent with a recovery process are identified and grouped by any convenient method. In a preferred method, fault queue 414 is expected to include faults of more than one ultimate cause. In one example of such a scenario, a CPU failure causes a burst of failure reports intermixed with a burst of failure reports caused by a simultaneous and unrelated IOSS failure. A chain of faults (fault --  chain), corresponding to the burst related to the CPU failure, for example, is formed and a recovery process is identified (fault --  recovery --  id). 
     In the implementation of the method illustrated in the Appendix, control returns from function MakeFltObject to function PollEvents and then to function ProcessFault, after construction of objects corresponding to fault signals received during the collection time. Grouping is accomplished with reference to equations from fault equation table 416 in the manner described in U.S. Pat. No. 5,220,662 to Lipton, incorporated herein by this reference. Faults that are determined to be consistent with an identified recovery process are eventually removed from fault queue 414. 
     In function ProcessFault, a while-loop is entered for selecting objects from fault queue 414. On each loop, a call is made to function Expert. Function Expert identifies fault objects consistent with one cause. Function Expert first scans fault queue 414 in its entirety to build array w --  FaultArray. This array is then passed to function LBEA --  FindFirstMatch, along with a reference to fault equation table 416. As a result of matching the array of faults to equations from the table, a value is assigned to the local variable wFltType, and a subset of queued faults is identified for linking. Linking to form a fault --  chain is accomplished by pointing pointer rFltRecord.pNext in the last fault object on the chain to the next fault object to be added to the chain. 
     The completed chain (fault --  chain) and local variable wFltType (fault --  recovery --  id) are passed to the next process step. 
     At step 420, fault recovery is dispatched for all fault objects identified by the fault --  chain. Dispatch is accomplished by any convenient method. In a preferred method, the local variable wFltType is used as an index into fault recovery table 419. A binary search of the table is implemented in function Expert after the fault --  chain has been formed. The indexed line of fault recovery table 419 includes a pointer to a recovery function as described above with reference to structure type T --  RFHL2TBLENTRY. Because each fault object conforms to the CFault interface, polymorphic methods accomplish standard functions in ways particular to each identified object. 
     Beneficial effects of dynamic binding for polymorphic fault objects can be better appreciated from an example of CPU failure. Consider the case wherein function MakeFItObject has constructed a CFaultCPU object. Later, function Expert has identified the BRFH --  RecoveryJupiterCPU recovery process for dispatch. When the system is not configured as a system having redundant multiple CPUs, a function call of the form pCpuFltObject-&gt;GotoSystemDisaster() is made from function BRFH --  RecoverJupiterCPU for the purpose of orderly shutdown. Since class CFauItCPU does not include an implementation of GotoSystemDisaster(), the parent function is inherited. 
     Function CFaultCss::GotoSystemDisaster() first identifies the releasable units (CPU, MU, IOU, IOSS, and SCU) currently operating by calling function BRFH --  MakeCssOruList. When a unit is released, it is operationally removed from System 100, i.e. its functions and cooperation are limited partially or completely. A for-loop provides a release step to be performed uniquely for each unit identified by a fault object in strucORUObjects. The loop accomplishes a release for each unit by transferring control to a polymorphic release function of each unit. The structure of this for-loop is independent of the units being released. Different units require unique operations to accomplish release, as illustrated by CFauItCPU::Release and CFaultMU::Release functions described in the Appendix. Dynamic binding associates the proper release function with each iterative call within the for-loop at run-time. 
     At step 422, fault objects identified on the fault --  chain are destructed to return allocated memory back to the system for reuse. For example, for the method described in the Appendix, the recovery process returns to function Expert where the function DelFltObject is called. The function DelFltObject is passed the head of the fault --  chain from which it can deallocate memory for each chained fault object, beginning with the last fault object in the chain. Control then returns to function PollEvents and then to the event driven operating system routine responsible for terminating execution of this instantiation of fault processor RFH. 
     
         __________________________________________________________________________100   // // // // // // // TYPE DEFINITIONS101   typedef struct / see Microsoft WIN31WH.HLP102  {103  HWND hwnd; // handle of fault processor&#39;s operating window104  UINT message;105  WPARAM wParam;106  LPARAM lParam;   // identifies REV107  DWORD time;108  POINT pt;109  } MSG;110   typdef struct111  {112  HANDLE hRev;  // REV used in object constructor113  WORD wEventId; // identifies unit providing fault message114  BYTE cbType;115  BYTE cbSystem;116  BYTE cbUnit;117  BYTE cbClass;   // identifies fault type118  BYTE cbSubClass;   // further identifies fault type119  int  iObjectType;120  WORD wFlags;121  WORD wFaultType;122  WORD wFaultMsg;123  WORD wSysAlarmNum;124  CFault* pNext;  // links fault objects into fault chain125  }T.sub.-- BASICRFHRECORD;126   typedef struct127  {128  WORD hWnd;129  CBRFHWindow* pMainWindow;130  CFault* pCurrentFaultObject;131  DWORD dwCleanupFlags;132  DWORD dwOptions;133  WORD wInitialCollectionTime;  // time in seconds for faults tocollect134  WORD wFaultThreshold;135  WORD wThresholdPeriod;136  WORD wOpeType;137  }T.sub.-- RFHGLOBAL;138   typedef struct139  {140  WORD wEntry[D.sub.-- EQLINESZ];141  } T.sub.-- RFHEQUATIONS;142   typedef struct143  {144  WORD wFltType;145  WORD (FAR PASCAL *pfnRecoverX) (CFault&amp;);146  } T.sub.-- RFHL2TBLENTRY;147   typedef struct148  {149  CFault* pObj[D.sub.-- MAXORUREC];150  } T.sub.-- ORUOBJECTS;151   typedef T.sub.-- ORUOBJECTS FAR* T.sub.-- LPORUOBJECTS;152   // // // // // // // DATA ITEMS153   COblist oblist.sub.-- FaultQueue(30);154   CBRFHWindow* p.sub.-- MainWnd;155   WORD FAR PASCAL BRFH.sub.-- RecoverJupiterCPU ( CFault&amp; P.sub.--   rFltObject );156   WORD FAR PASCAL BRFH.sub.-- RecoverSysDisaster ( CFault&amp; P.sub.--   rFltObject );157   T.sub.-- RFHGLOBAL struc.sub.-- RFHGlobal;158   T.sub.-- RFHEQUATIONS struc.sub.-- RFHEQTbl[D.sub.-- RFHEQTBLSZ] =159  {160  {D.sub.-- F3100,0x0301,D.sub.-- F31C1,DSP.sub.-- AND,D.sub.--F31C0,161    DSP.sub.-- END,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,162    0,0,0,0,0,0,0,0,0,0},163  {D.sub.-- F3100,0x0101,D.sub.-- F31C1,  // fatal CPU error164    D.sub.-- F3100,0x0101,D.sub.-- F31C0,  // non-fatal CPU error165    D.sub.-- F3100,0x0101,D.sub.-- F31C2,  // parity error on SSP166    D.sub.-- F3100,0x0101,D.sub.-- F31C3,  // DIAG TAG 0 - BPU Freeze167    D.sub.-- F3100,0x0101,D.sub.-- F31C4,  // DIAG TAG 21168    D.sub.-- F3100,0x0101,D.sub.-- F31C5,  // address trap169    D.sub.-- F3100,0x0101,D.sub.-- F31C6,  // DIAG TAG 0 - Fault on  Fault170    D.sub.-- F3100,0x0101,D.sub.-- F31CD,  // ONC Event171    D.sub.-- F3100,0x0101,D.sub.-- F31CE,172    DSP.sub.-- OR,D.sub.-- F31CF,      // unexpected events173    DSP.sub.-- END,0,0},174  {D.sub.-- FC000,0x0F01,D.sub.-- F11E0,DSP.sub.-- OR,175    D.sub.-- F11E1,DSP.sub.-- OR,D.sub.-- F4145,DSP.sub.-- OR,176    D.sub.-- F6135,DSP.sub.-- OR,D.sub.-- F61F1,DSP.sub.-- OR,177    D.sub.-- F61F2,DSP.sub.-- OR,D.sub.-- F6134,DSP.sub.-- OR,178    D.sub.-- F1800,179    DSP.sub.-- END,0,0,0,0,0,0,0,0,0,0,0,0,0,0,},180  {D.sub.-- FC000,0x1301,D.sub.-- F5154,DSP.sub.-- OR,181    D.sub.-- F5156,DSP.sub.-- OR,D.sub.-- F515C,DSP.sub.-- OR,182    D.sub.-- F41F1,DSP.sub.-- OR,D.sub.-- F41F2,DSP.sub.-- OR,183    D.sub.-- F41F8,DSP.sub.-- OR,D.sub.-- F41FE,DSP.sub.-- OR,184    D.sub.-- F61F6,DSP.sub.-- OR,D.sub.-- F61F7,DSP.sub.-- OR,185    D.sub.-- F61F8,186    DSP.sub.-- END,0,0,0,0,0,0,0,0,0,0}187  };188   T.sub.-- RFHL2TBLENTRY struc.sub.-- RFHL2Tb1 [D.sub.-- RFHL2TBLSZ] =189  {190  {D.sub.-- F3100, BRFH.sub.-- RecoverJupiterCPU},191  {D.sub.-- FC000, BRFH.sub.-- RecoverSysDisaster};192  };193   DSP.sub.-- CB0UNITNBR = 101;194   IDSSP.sub.-- EVCS00 = 0;195   IDSSP.sub.-- EVCS03 = 1;196   D.sub.-- F0002 = 0x0002; / unknown fault197   D.sub.-- F1001 = 0x1001;198   D.sub.-- F1002 = 0x1002;199   D.sub.-- F1003 = 0x1003;200   D.sub.-- F3100 = 0x3100;201   D.sub.-- FC000 = 0xC000;202   D.sub.-- CSSOTYPCPU = 1011;203   D.sub.-- CSSOTYPMU = 1012;204   D.sub.-- RFHL2TBLSZ = 8192;205   D.sub.-- EQLINESZ = 128;206   DSP.sub.-- DONE = 0;207   DSP.sub.-- ENDTABLE = 8192 - 128;208   DSP.sub.-- SYMUSED = 1;209   // // // // // // // CLASSES AND INTERFACES210   class CFault : public COBject211   {212   public:213  CFault( );214  CFault(T.sub.-- BASICRFHRECORD&amp; P.sub.-- rFltRecord);215  virtual BOOL ReleaseUnit( )=0;216  virtual void DumpHardware(void)=0;217  virtual void GotoSystemDisaster( ) = 0;218  virtual ˜CFault( );219   protected:220  T.sub.-- BASICRFHRECORD m.sub.-- FltRecord;221   }222   class CFaultCss : public CFault223   {224   public:225  CFaultCss( );226  CFaultCss(T.sub.-- BASICRFHRECORD&amp; P.sub.-- rFltRecord);227  void DumpHardware( );228  void DumpHardware(TSP.sub.-- LPHWDUMPLIST P.sub.-- lpList);229  void GotoSystemDisaster( );230   }231   class CFaultCPU : public CFaultCss232   {233   public:234  CFaultCPU( );235  CFaultCPU(T.sub.-- BASICRFHRECORD&amp; P.sub.-- rFltRecord);236  BOOL ReleaseUnit(void);237  void DumpHardware(void);238   }239   class CFaultMU : public CFaultCss240   {241   public:242  CFaultMU( ):CFaultCss( ) { }  // default constructor243  CFaultMU(T.sub.-- BASICRFHRECORD&amp; P.sub.-- rFltRecord):244    CFaultCss(P.sub.-- rFltRecord)   { }245  BOOL ReleaseUnit( );246  const BYTE GetUnitNum( ) {return(m.sub.-- FltRecord.cbUnit -247    DSP.sub.-- MU0UNITNBR);}  // returns MU number248  BOOL CheckMultiUnit(void);249  void ClearMemoryErrors( );250  ˜CFaultMU( ) { }251   };252   class CBRFHWindow : public CBodyXMSWindow253   {254   public:255  CBRFHWindow(char* P.sub.-- szVersion);256  WORD ProcessFault (WORD P.sub.-- wCollectionTime);257  WORD PollEvents (WORD P.sub.-- wCollectionTime =258    DSP.sub.-- MINCOLLECTIONTIME);259  BOOL IsFault(MSG P.sub.-- msg);260  void Expert (void);261  WORD EnQueue(CFault* P.sub.-- pFltObject);262  CFault* DeQueue(void);263  void DelFltObject (CFault* P.sub.-- pFltObject);264   }265   class CFactory : public CObject266   {267   public:268  CFactory( ) { }269  virtual ˜CFactory( ) { }270  CFault* MakeFltObject(MSG P.sub.-- msg);271   }272   // // // // // // // MEMBER FUNCTIONS273   WORD CBRFHWindow::ProcessFault (WORD P.sub.-- wCollectionTime)274   {275   WORD wStatus = 0xFFFF;276   wStatus = PollEvents(P.sub.-- wCollectionTime);277   while (!oblist.sub.-- FaultQueue.IsEmpty( ))278  {279  Expert( );280  if (oblist.sub.-- FaultQueue.IsEmpty( ))281    wStatus = PollEvents(DSP.sub.-- MINCOLLECTIONTIME);282  }283   return(0);284   }285   WORD CBRFHWindow::PollEvents (WORD P.sub.-- wCollectionTime)286   {287   BOOL bMsgExists;288   WORD wStatus;289   MSG msg;290   Wait(P.sub.-- wCollectionTime);291   while (bMsgExists=LXYS.sub.-- PeekThisMessage(&amp;msg,292  (HWND)struc.sub.-- RFHGlobal.hWnd,293  WM.sub.-- DDE.sub.-- DATA, WM.sub.-- DDE.sub.-- POKE,0, 0, 0,DSP.sub.-- MESS.sub.-- REMOVE))294  {295  if(IsFault(msg))296    {297    CFault* pFltObject = p.sub.-- Factory--&gt;MakeFltObject(msg);298    wStatus = EnQueue(pFltObject);299    }300  }301   return(0);302   }303   CFault* CFactory::MakeFltObject(MSG P.sub.-- msg)304   {305   T.sub.-- BASICRFHRECORD strucFltRecord;306   CFault* pFltObject = NULL;307   strucFltRecord.WEventId = LXSYS.sub.-- GetAtomIndex( HIWORD( P.sub.--   msg.lParam308   ));309   if((strucFltRecord.wEventId &gt;= IDSSP.sub.-- EVCS00) &amp;&amp;310  strucFltRecord.wEventId &lt;= IDSSP.sub.-- EVCS03))311  {312  BRFH.sub.-- AnalyzeCSSFault(strucFltRecord);313  switch(strucFltRecord.iObjectType);314    {315  case D.sub.-- CSSOTYPCPU:316    pFltObject = new CFaultCPU(strucFltRecord);317    break;318  case D.sub.-- CSSOTYPMU:319    pFltObject = new CFaultMU(strucFltRecord);320    break;321  ...construct objects for other types of faults...322    }323  }324   else325  {326  ...analyze and construct objects from other unit types...327  }328   return (pFltObject);329   }330   void FAR PASCAL BRFH.sub.-- AnalyzeCSSFault(T.sub.-- BASICRFHRECORD&amp;331   P.sub.-- rFltRecord)332   {333   WORD wFltType;334   switch p.sub.-- FltRecord.cbClass335  {336   case 0x01:337  wFltType = D.sub.-- F1001;338  P.sub.-- rFltRecord.wFaultType = wFltType;339  p.sub.-- rFltRecord.iObjectType = D.sub.-- CSSOTYPCPU;340  break;341   case 0x02:342  wFltType = D.sub.-- F1002;343  P.sub.-- rFltRecord.wFaultType = wFltType;344  p.sub.-- rFltRecord.iObjectType = D.sub.-- CSSOTYPMU;345  break;346  ...etc...347  }348   return;349   }350   void CBRFHWindow::Expert (void)351   {352   INT i, iNumFaults;353   WORD wStatus, wFltType;354   DWORD dwResults;355   CFault* pFltObject, pFirstFault, pCurrentFault;356   for (i = 0; i &lt; iNumFaults; i++)357  {358  pFltObject = DeQueue( );359  T.sub.-- BASICRFHRECORD&amp; rFltRecord =360    pFltObject--&gt;GetFltRecord( );361  w.sub.-- FaultArray[i+1] = rFltRecord.wFaultType;362  EnQueue(pFltObject);363  w.sub.-- FaultArray[0]++;364  }365   dwResults = LBEA.sub.-- FindFirstMatch ((LPWSTR)&amp; w.sub.-- FaultArray[0   ],366  (LPWSTR)&amp; struc.sub.-- RFHEQTbl[0].wEntry[0]);367   if((LOWORD(dwResults) == DSP.sub.-- DONE) ∥368  (LOWORD(dwResults) == DSP.sub.-- ENDTABLE))369  {370  wFltType = HIWORD(dwResults);371  pFirstFault = NULL;372  bFound = FALSE;373  i = 0;374  while (!bFound &amp;&amp; (i &lt; iNumFaults))375    {376    pFltObject = DeQueue( ); // pull from front377    if (w.sub.-- FaultArray[i+1] != DSP.sub.-- SYMUSED)378      {379      EnQueue(pFltObject); // rtn to end380      i++;381      }382    else383      {384      bFound = TRUE;385      pFirstFault = pFltObject;386      i++;387      }388    }389  pCurrentFault = pFirstFault;390  while (i &lt; iNumFaults)391    {392    pFltObject = DeQueue( );    // off the front393    if (w.sub.-- FaultArray[i+1] != DSP.sub.-- SYMUSED)394      {395      EnQueue(pFltObject); // on the end396      i++;397      }398    else399      {400      T.sub.-- BASICRFHRECORD&amp; rFltRecord =401      pCurrentFault--&gt;GetFltRecord( );402      rFltRecord.pNext = pFltObject;403      pCurrentFault = pFltObject;404      i++;405      }406    }407  iTop = 0;408  iBottom = D.sub.-- RFHL2TBLSZ - 1;409  do410    {411    wIndex = (iTop + iBottom)/2;412    if(wFltType &gt; struc.sub.-- RFHL2Tbl[wIndex].wFltType)413      iTop = (int)wIndex + 1;414    else415      iBottom = (int)wIndex - 1;416    } while ((iTop &lt;= iBottom) &amp;&amp;417    (struc.sub.-- RFHL2Tbl[wIndex].wFltType != wFltType));418  if (LOWORD(dwResults) == DSP.sub.-- ENDTABLE)419    pFirstFault = DeQueue( );420  if(struc.sub.-- RFHL2Tbl[wIndex].wFltType != wFltType)421    wIndex = D.sub.-- F0002; /* unknown */422  wStatus =423  (*(struc.sub.-- RFHL2Tbl[wIndex].pfnRecoverX))((CFault&amp;)*pFirstFault);424  struc.sub.-- RFHGlobal.pCurrentFaultObject = NULL;425  DelFltObject (pFirstFault);426  }427   return;428   }429   WORD FAR PASCAL BRFH.sub.-- Recover JupiterCPU(CFault&amp; P.sub.--   rFltObject)430   {431   CFault* pChainedFlt;432   CFaultCPU* pCpuFltObject = (CFaultCPU*)&amp;P.sub.-- rFltObject;433   T.sub.-- BASICRFHRECORD &amp; rFltRecord = pCpuFltObject--&gt;GetFltRecord(   );434   switch (rFltRecord.wFaultType)435  {436   case: D.sub.-- F31C0437  pChainedFlt = pCpuFltObject--&gt;GetChainedFault( );438  if(pChainedFlt != NULL)439    {440    pCpuFltObject--&gt;PrintNote(&#34;Processing CPU Fault(s) Belonging441      to a Known Event Scenario&#34;);442    BRFH.sub.-- RecoverJupiterCPU((CFault&amp;)*pChainedFlt);443    char szSeparator[80];444    p.sub.-- MainWnd--&gt;MakeMessage(IDS.sub.-- ALMSEPARATOR,445  szSeparator);446    p.sub.-- MainWnd--&gt;PrintLogi(szSeparator);447    pCpuFltObject--&gt;PrintNote(&#34;Continuing Processing of the original448      31C0 CPU Fault&#34;);449    }450  if(!bMultiCPU)451    {452    pCpuFltObject--&gt;PrintAction(&#34;Single CPU System -453      Going to System Disaster&#34;);454    pCpuFltObject--&gt;GotoSystemDisaster( );455    }456  else457    {458    pCpuFltObject--&gt;ReleaseUnit( );459    pCpuFltObject--&gt;DumpHardware( );460    }461  break;462   case //other error codes463  ... etc. ...464  }465   }466   WORD FAR PASCAL BRFH.sub.-- RecoverSysDisaster (CFault&amp; P.sub.--   rFltObject)467   {468   CFaultCss&amp; rFltCssObject = (CFaultCss&amp;)P.sub.-- rFltObject;469   rFltCssObject.GotoSystemDisaster( );470   return (0);471   }472   void CFaultCss::GotoSystemDisaster(void)473   {474   WORD wstatus;475   BYTE i;476   BYTE cbNumUnits;477   T.sub.-- ORUOBJECTS strucORUObjects;478   BYTE cbsystem = GetSystem( );479   wStatus = BRFH.sub.-- MakeCssOruList ((CFaultCss*)this, (T.sub.--   LPORUOBJECTS)&amp;480  strucORUObjects);481   cbNumUnits = 0;482   for (i = 0; i &lt; D.sub.-- MAXORUREC; i++)483  {484  if(strucORUObjects.pObj[i] != NULL)485  cbNumUnits ++;486  }487   for (i = 0; i &lt; cbNumUnits; i++)488  strucORUObjects.pObj[i]--&gt;ReleaseUnit( );489   for (i = 0; i &lt; cbNumUnits; i++)490  strucORUObjects.pObj[i]--&gt;DumpHardware( );491   }492   WORD FAR PASCAL BRFH.sub.-- MakeCssOruList (CFaultCss* P.sub.--   pFltObject,493  T.sub.-- LPORUOBJECTS P.sub.-- lpORUObjects)494   {495   CFaultCss* pFltObject;496   CFaultCss* pFltObject1;497   CFaultCss* pFltObject2;498   CFaultCss* pFltObject3;499   BYTE i;500   pFltObject = NULL;501   pFltObject1 = P.sub.-- pFltObject;502   pFltObject2 = NULL;503   pFltObject3 = NULL;504   P.sub.-- lpORUObjects--&gt;pObj[0] = P.sub.-- pFltObject;505   for (i = 1; i &lt; D.sub.-- MAXORUREC; i++)506  P.sub.-- lpORUObjects--&gt;pOBj[i] = NULL;507   i = 1;508   pFltObject = (CFaultCss*)pFltObject1--&gt;GetChainedFault( );509   while ((pFltObject != NULL) &amp;&amp; (i &lt; D.sub.-- MAXORUREC))510  {511  T.sub.-- BASICRFHRECORD&amp; rFltRecord = pFltObject--&gt;GetFltRecord( );512  T.sub.-- BASICRFHRECORD&amp; rFltRecord1 = pFltObject1--&gt;GetFltRecord();513  BOOL bUsed = FALSE;514  if((rFltRecord.cbUnit != rFltRecord1.cbUnit) ∥ (rFltRecord.cbType515    != rFltRecord1.cbType))516    {517    pFltObject2 = pFltObject;518    P.sub.-- lpORUObjects--&gt;pObj[i] = pFltObject;519    bUsed = TRUE;520    i++;521    }522  if((bUsed == FALSE) &amp;&amp; (pFltObject2 != NULL))523    {524    T.sub.-- BASICRFHRECORD&amp; rFltRecord2 =525   pFltObject2--&gt;GetFltRecord( );526    if((rFltRecord.cbUnit != rFltRecord2.cbUnit) ∥ (rFltRecord  .cbType)527      != rFltRecord2.cbType))528      {529      pFltObject3 = pFltObject;530      P.sub.-- lpORUObjects--&gt;pObj[i] = pFltObject;531      bUsed = TRUE;532      i++;533      }534    }535  FltObject = (CFaultCss*)pFltObject--&gt;GetChainedFault( );536  }537   return (0);538   }539   BOOL CFaultCPU::ReleaseUnit( )540   {541   SPFBARFCommand BARFCommand;542   char szMsg[80];543   BYTE cbReason;544   BYTE cbUnitNum = GetUnitNum( );545   wsprintf(szMsg, &#34;Releasing CPU%d&#34;, cbUnitNum);546   PrintAction(szMsg);  // print action message547   if(!CheckMultiUnit( ))548  // this check necessary for system disaster releases.549  {550  wsprintf(szMsg, &#34;CPU%d not Released - Single-CPU System&#34;,551   cbUnitNum);552  PrintResult(szMsg);553  return FALSE;554  }555   if FOS.sub.-- ENABLED(D.sub.-- ENABLEDEF)556  // Check FOS option for how to release this unit557  cbReason = DSP.sub.-- ARFDEFECTIVE;  // release DEFECTIVE558   else559  // release OTHER so RCF can re-assign (for debug)560  cbReason = DSP.sub.-- ARFALLOTHER;561   m.sub.-- hACB = BARFCommand.BuildCPUCmdBlock(DSP.sub.-- ARFEXECUTE,562   DSP.sub.-- ARFRELEASE, cbReason, cbUnitNum, GetArfSysNum( ));563   return CFault::ReleaseUnit( );564   ERROR.sub.-- EXIT:565  PrintResult(&#34;Error Releasing Unit&#34;);566  return FALSE;567   }568   BOOL CfaultMU::ReleaseUnit( )569   {570   SPFBARFCommand BARFCommand;571   char szMsg[80];572   BYTE cbReason;573   BYTE cbUnitNum = GetUnitNum( )574   wsprintf(szMsg, &#34;Releasing MU%d&#34;, cbUnitNum);575   PrintAction(szMsg);  // print action message576   if (!CheckMultiUnit( )) // don&#39;t release the only MU on the system577  {578  wprintf(szMsg, &#34;MU%d not Released - Single-MU System&#34;,579   cbUnitNum);580  PrintResult(szMsg);581  return FALSE;582  }583   if FOSENABLED(D.sub.-- ENABLEDEF)584  // Check FOS option for how to release this unit585  cbReason = DSP.sub.-- ARFDEFECTIVE; // release DEFECTIVE586   else587  // release OTHER so RCF can re-assign (for debug)588  cbReason = DSP.sub.-- ARFALLOTHER;589   m.sub.-- hACB = BARFCommand.BuildMUCmdBlock(DSP.sub.-- ARFEXECUTE,590   DSP.sub.-- ARFRELEASE, cbReason, cbUnitNum, GetArfSysNum( ));591   return CFault::ReleaseUnit( );592   ERROR.sub.-- EXIT:593  PrintResult(&#34;Error Releasing Unit&#34;);594  return FALSE;595   }596   BOOL CFault::ReleaseUnit( )597   {598   SPFBARFCommand BARFCommand;599   TSP.sub.-- LPARFCMDBLOCK lpARFCmd;600   DWORD dwStatus;601   char szMsg[80];602   if (!m.sub.-- hACB)603  NONFATAL.sub.-- EXIT(m.sub.-- hACB, m.sub.-- FltRecord.cbUnit);604   // set RFH-specific flags605   if(!(lpARFCmd = (TSP.sub.-- LPARFCMDBLOCK)GlobalLock (m.sub.--   hACB)))606  NONFATAL.sub.-- EXIT (m.sub.-- hACB, D.sub.-- ERROR)607   lpARFCmd--&gt; bForce = TRUE;608   // this flag tells BARF that RFH is calling: release CPU by Shutdown   Fault only609   lpARFCmd--&gt;bFault = TRUE;610   if (GlobalUnlock (m.sub.-- hACB))611  NONFATAL (m.sub.-- hACB, D.sub.-- ERROR)612   // Execute the Unit Release613   if (BARFCommand.Start( ))  // Start up ARF and the DDE Session614  {615  // PostMessage and wait for DDE Ack616  dwStatus = BARFCommand.SendDDE(m.sub.-- hACB);617  m.sub.-- hACB = NULL;  // the handle was freed by the Service Cmdobject618  // Loword is status. Both are null if no response.619  if (!dwStatus)620    {621    PrintResult(&#34;Timeout waiting for ARF to ReleaseUnit&#34;);622    return FALSE;623    }624  if (LOWROD(dwStatus) != DSP.sub.-- DONE)625    {626    wsprintf(szMsg, &#34;Error Releasing Unit - ARF Status627      = %081x&#34;, dwStatus);628    PrintResult(szMsg);629    return FALSE;630    }631  }632   else // Could not start ARF633  {634  PrintResult(&#34;Error Starting ARF - Unit not Released&#34;);635  GlobalFree(m.sub.-- hACB);636  m.sub.-- hACB = NULL;637  return FALSE;638  }639   PrintResult(&#34;Unit Successfully Released&#34;);640   return TRUE;641   ERROR.sub.-- EXIT:642  PrintResult(&#34;Error Releasing Unit&#34;);643  return FALSE;644   }__________________________________________________________________________