Abstract:
Methods and systems consistent with the present invention allow a program designer to conveniently specify and support watchdog checking of a program under development. The resulting programs are more robust than programs developed without watchdog support. The method and systems provide a convenient, automated mechanism for adding watchdog support to a program. Thus, a developer need not incur the substantial time and effort costs that would be associated with manually designing and configuring separate watchdog programs. Rather, the methods and systems provide substantial assistance to the developer in designing a robust program.

Description:
CROSS REFERENCE  
       [0001]     This application is a continuation of U.S. application Ser. No. 10/241,097 filed Sep. 11, 2002. This application claims priority to the foregoing application, which application is incorporated herein by reference to the extent permitted by law. 
     
    
     FIELD OF THE INVENTION  
       [0002]     This invention relates to fault detection and recovery in software systems. In particular, this invention relates to adding watchdog support to program code and to a supporting software library of watchdog routines.  
       BACKGROUND OF THE INVENTION  
       [0003]     Certain computer systems need to provide service to customers even in the face of arbitrary combinations of hardware and software failures. Of course, there are some combinations of failures that can disable even the most robust system regardless of the reliability measures that are incorporated into the system. Nevertheless, systems that must be highly available can benefit from a design and implementation that provides for some robustness, for example, through failure detection or recovery.  
         [0004]     Designing robust systems can be a difficult task, particularly when complex software (e.g., operating systems and customer applications) interacts with complex hardware. Software tools that assist with creating a robust program are generally cumbersome to use and require significant manual intervention by the designer. As a result, the software tools are not used, and the resulting software is not as robust as it otherwise could be.  
         [0005]     Therefore, a need has long existed for fault monitoring, detection, and recovery functionality that overcomes the problems noted above and others previously experienced.  
       SUMMARY OF THE INVENTION  
       [0006]     Methods and systems consistent with the present invention provide a mechanism for conveniently specifying and supporting watchdog checking of a program under development. The methods and systems thus allow a developer to add watchdogs to a program under development without expending an inordinate amount of time and effort. As a result, the programs under development become more robust than programs developed without watchdog support.  
         [0007]     According to one aspect of the present invention, such methods and systems, as embodied and broadly described herein, include reading a watchdog specification for a code block, and inserting into the code block a watchdog setup call and a watchdog reporting call. As a result, the developer may insert watchdog specifications at any desired code blocks in the program and allow the compiler, in an automated fashion, to handle the detailed implementation and support of the specified watchdog. Thus, the methods and systems assist the developer in making the program more robust.  
         [0008]     Methods and systems consistent with the present invention overcome the shortcomings of the related art, for example, by providing a convenient, automated mechanism for adding watchdog support to a program. Thus, a developer need not incur the substantial time and effort costs that would be associated with manually designing and configuring separate watchdog programs. Rather, methods and systems consistent with the present invention provide substantial assistance to the developer in designing a robust program.  
         [0009]     In accordance with methods consistent with the present invention, a method is provided for adding watchdog support to a program. The method includes reading a watchdog specification for a code block, inserting a watchdog setup call into the program before the code block, and inserting a watchdog reporting call into the code block.  
         [0010]     In accordance with systems consistent with the present invention, a data processing system is provided. The data processing system includes a memory comprising a compiler, the compiler reading a watchdog specification for a code block, inserting a watchdog setup call into the program before the code block, and inserting a watchdog reporting call into the code block. The data processing system also includes a processor that runs the compiler.  
         [0011]     In addition, a computer-readable medium is provided. The computer-readable medium contains instructions that cause a data processing system to perform a method for adding watchdog support to a program comprising code blocks. The method includes reading a watchdog specification for a code block, inserting a watchdog setup call into the program before the code block, and inserting a watchdog reporting call into the code block.  
         [0012]     Other apparatus, methods, features and advantages of the present invention will be or will become apparent to one with skill in the art upon examination of the following figures and detailed description. It is intended that all such additional systems, methods, features and advantages be included within this description, be within the scope of the present invention, and be protected by the accompanying drawings. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0013]      FIG. 1  depicts a block diagram of a data processing system suitable for practicing methods and implementing systems consistent with the present invention.  
         [0014]      FIG. 2  depicts an example of watchdog specifiers and code blocks present in source code stored in the memory of the data processing system shown in  FIG. 1 , as well as watchdog support instructions added by a compiler running in the memory of the data processing system shown in  FIG. 1 .  
         [0015]      FIG. 3  depicts a flow diagram of the steps taken by a compiler running in the data processing system shown in  FIG. 1  to add watchdog support to source code stored in the memory of the data processing system of  FIG. 1 .  
         [0016]      FIG. 4  depicts a flow diagram of the steps taken by a watchdog completion function running in the memory of the data processing system shown in  FIG. 1  when a watchdog is no longer needed to monitor a code block.  
         [0017]      FIG. 5  depicts a flow diagram of a watchdog reporting call that informs a watchdog running in the data processing system shown in  FIG. 1  that a program has reached a specified point in its execution.  
         [0018]      FIG. 6  depicts a flow diagram of a watchdog status function running in the data processing system shown in  FIG. 1  for determining heartbeat timing parameters for a specified watchdog.  
         [0019]      FIG. 7  depicts a flow diagram of a watchdog status function running in the data processing system shown in  FIG. 1  for setting heartbeat timing parameters for a specified watchdog.  
         [0020]      FIG. 8  depicts a flow diagram of the steps taken by a watchdog when monitoring execution of a code block running in the data processing system shown in  FIG. 1 . 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0021]     Reference will now be made in detail to an implementation in accordance with methods, systems, and products consistent with the present invention as illustrated in the accompanying drawings. The same reference numbers may be used throughout the drawings and the following description to refer to the same or like parts.  
         [0022]      FIG. 1  depicts a block diagram of a data processing system  100  suitable for practicing methods and implementing systems consistent with the present invention. The data processing system  100  comprises a central processing unit (CPU)  102 , an input output I/O unit  104 , a memory  106 , a secondary storage device  108 , and a video display  110 . The data processing system  100  may further include input devices such as a keyboard  112 , a mouse  114  or a speech processor (not illustrated).  
         [0023]     An operating system  116  (e.g., UNIX, Solaris, or the like) runs in the memory  106 . A compiler  118  is available to program developers and may be invoked to compile the source code  120 . In one embodiment, the compiler  118  reads watchdog specifications  122  in the source code  120  and responsively adds watchdog functionality when forming the program object code  124  (and thus the resultant executable  142 ). The compiler  118  may add, as examples, watchdog setup calls  126 , watchdog reporting calls  128 , and watchdog completion calls  130  to the object code  124 .  
         [0024]     The watchdog setup calls  126  are responsible in part for initiating execution of subroutines to establish the watchdogs  130 ,  132 , and  134 . The watchdog  130  is a watchdog thread that watches over code blocks associated with a thread-level threat. The watchdog  132  is a watchdog program that watches over code blocks associated with a program-level threat. The watchdog  134  is a watchdog program whose execution is initiated on a separate data processing system  136  to monitor code block execution on the data processing system  102  that pose a machine-level threat to the data processing  102 . The threat levels are discussed in more detail below.  
         [0025]     In general, a watchdog is a piece of code inserted by the compiler that monitors execution of a code block to detect execution abnormality of either the software or the hardware or software. For example, the watchdog may detect when a program code block hangs, enters an infinite loop, or causes the program to abnormally terminate.  
         [0026]     The memory  106  also holds a watchdog status table  138 . The status table  138  stores parameters relevant to the execution of the watchdogs  130 - 134 . The data processing system  136  (which may be implemented in the same manner as the data processing system  100 ) may store its own watchdog status table  138 . As will be explained in more detail below, the watchdogs  130 - 134  operate according to the parameters provided for them in the watchdog status table  138  and in a local parameter table  144  associated with each watchdog  130 - 134 . The watchdog support library  140  provides the functions that implement the watchdog setup calls  126 , watchdog reporting calls  128 , watchdog completion calls  130 , and additional watchdog support calls discussed below.  
         [0027]     Although aspects of the present invention are depicted as being stored in memory  106 , one skilled in the art will appreciate that all or part of systems and methods consistent with the present invention may be stored on or read from other computer-readable media, for example, secondary storage devices such as hard disks, floppy disks, and CD-ROMs; a signal received from a network such as the Internet; or other forms of ROM or RAM either currently known or later developed. Further, although specific components of data processing system  100  are described, one skilled in the art will appreciate that a data processing system suitable for use with methods, systems, and articles of manufacture consistent with the present invention may contain additional or different components.  
         [0028]     The watchdog specifications  122  are associated with code blocks in the source code  120 . A code block is one or more source code statements in the source code  120 . As examples, the code block for a loop generally includes all the statements forming the loop (with the watchdog specification placed immediately before the loop), while a code block for sequential statements may be bounded using braces (‘{’, ‘}’) (or other pre-selected characters).  FIG. 2  shows an example of a watchdog specifier  202  associated with a “while” loop code block  204  and an example of a watchdog specifier  206  associated with a non-loop code block  208  (bounded using braces).  
         [0029]     In one implementation, as shown in  FIG. 2 , the watchdog specifications  202  and  206  take the form of “pragma” statements read and interpreted by the compiler  118  with the form shown below in Table 1:  
                         TABLE 1                           #pragma watch(condition_list, signal=signum | call=userfunc [,max_heartbeats=nn]       [,heart_rate=nn] [,event_handle=variable]       [,userlib=path_to_shared_library_containing_user_code]).            Parameter   Comment               condition_list   This parameter provides a list of events for which the watchdog           should watch. It can be a comma-separated list of: ‘hang’ and ‘abort’.           A ‘hang’ means that a program has not made progress in a           specified amount of time. An ‘abort’ means that a program has           abnormally terminated.       signal   The parameter ‘signal’ is the signal that should be sent to the           thread if the watchdog event is detected. It can be either an           integer or a symbolic value representing a legal signal. In UNIX           systems, for example, the signal symbols can be imported by a           variety of means           including using one or more of these statements:           #include &lt;signal.h&gt;           #include &lt;sys/signal.h&gt;           #include &lt;sys/iso/signal_iso.h&gt;           See Table 3 for a list of the signals imported by the statements           above. The signals are illustrative only; and signals recognized           by the data processing system 100 may be used.       call   The parameter ‘call’ identifies a function to be called if an event           is detected. The function will receive as its argument the event           handle of the event that was detected. The parameters call and           signal are, in one embodiment, mutually exclusive.       max_heartbeats   The parameter ‘max_heartbeats’ specifies the number of           heartbeats that the program can send before the watchdog will           conclude that the thread or program is hung (e.g., in an infinite           loop). If max_heartbeats is not specified then there is no limit.       heart_rate   The parameter ‘heart_rate’ specifies the rate at which           heartbeats must arrive. If two heartbeats are separated in time           by more than heart_rate (measured, e.g., in seconds or           milliseconds) then the watchdog may conclude that the thread is           hung. If heart_rate is not specified then there is no minimum           heart rate. If condition_list includes “hung” then           max_heartbeats, heart_rate, or both may be specified.       event_handle   The parameter ‘event_handle’ specifies a variable of type           wd_event_handle_t into which the event handle will be written           when the watchdog is initialized.       userlib   The parameter ‘userlib’ provides the file system path to a           function library that includes the function specified by the ‘call’           parameter.                  
 
         [0030]    
       
         
               
               
             
           
               
                 TABLE 3 
               
               
                   
               
               
                   
               
               
                 Signal 
                 Comment 
               
               
                   
               
             
             
               
                 #define SIGHUP 1 
                 /* hangup */ 
               
               
                 #define SIGINT 2 
                 /* interrupt (rubout) */ 
               
               
                 #define SIGQUIT 3 
                 /* quit (ASCII FS) */ 
               
               
                 #define SIGILL 4 
                 /* illegal instruction (not reset when 
               
               
                   
                 caught) */ 
               
               
                 #define SIGTRAP 5 
                 /* trace trap (not reset when caught) */ 
               
               
                 #define SIGIOT 6 
                 /* IOT instruction */ 
               
               
                 #define SIGABRT 6 
                 /* used by abort, replace SIGIOT in 
               
               
                   
                 the future */ 
               
               
                 #define SIGEMT 7 
                 /* EMT instruction */ 
               
               
                 #define SIGFPE 8 
                 /* floating point exception */ 
               
               
                 #define SIGKILL 9 
                 /* kill (cannot be caught or ignored) */ 
               
               
                 #define SIGBUS 10 
                 /* bus error */ 
               
               
                 #define SIGSEGV 11 
                 /* segmentation violation */ 
               
               
                 #define SIGSYS 12 
                 /* bad argument to system call */ 
               
               
                 #define SIGPIPE 13 
                 /* write on a pipe with no one to read it */ 
               
               
                 #define SIGALRM 14 
                 /* alarm clock */ 
               
               
                 #define SIGTERM 15 
                 /* software termination signal from kill */ 
               
               
                 #define SIGUSR1 16 
                 /* user defined signal 1 */ 
               
               
                 #define SIGUSR2 17 
                 /* user defined signal 2 */ 
               
               
                 #define SIGCLD 18 
                 /* child status change */ 
               
               
                 #define SIGCHLD 18 
                 /* child status change alias (POSIX) */ 
               
               
                 #define SIGPWR 19 
                 /* power-fail restart */ 
               
               
                 #define SIGWINCH 20 
                 /* window size change */ 
               
               
                 #define SIGURG 21 
                 /* urgent socket condition */ 
               
               
                 #define SIGPOLL 22 
                 /* pollable event occured */ 
               
               
                 #define SIGIO SIGPOLL 
                 /* socket I/O possible (SIGPOLL alias) */ 
               
               
                 #define SIGSTOP 23 
                 /* stop (cannot be caught or ignored) */ 
               
               
                 #define SIGTSTP 24 
                 /* user stop requested from tty */ 
               
               
                 #define SIGCONT 25 
                 /* stopped process has been continued */ 
               
               
                 #define SIGTTIN 26 
                 /* background tty read attempted */ 
               
               
                 #define SIGTTOU 27 
                 /* background tty write attempted */ 
               
               
                 #define SIGVTALRM 28 
                 /* virtual timer expired */ 
               
               
                 #define SIGPROF 29 
                 /* profiling timer expired */ 
               
               
                 #define SIGXCPU 30 
                 /* exceeded cpu limit */ 
               
               
                 #define SIGXFSZ 31 
                 /* exceeded file size limit */ 
               
               
                 #define SIGWAITING 32 
                 /* process&#39;s lwps are blocked */ 
               
               
                 #define SIGLWP 33 
                 /* special signal used by thread library */ 
               
               
                 #define SIGFREEZE 34 
                 /* special signal used by CPR */ 
               
               
                 #define SIGTHAW 35 
                 /* special signal used by CPR */ 
               
               
                 #define SIGCANCEL 36 
                 /* thread cancellation signal used 
               
               
                   
                 by libthread */ 
               
               
                 #define SIGLOST 37 
                 /* resource lost (eg, record-lock lost) */ 
               
               
                 #define SIGXRES 38 
                 /* resource control exceeded */ 
               
               
                   
               
             
          
         
       
     
         [0031]     As the compiler  118  reads the source code  120 , the compiler  118  encounters the watchdog specifications. The compiler  118  parses the watchdog specifications and identifies the associated code block. To that end, the compiler  118  may identify the statements that comprise a loop, or identify an opening and closing brace character that surround a non-loop code block.  
         [0032]     For each watchdog specification, the compiler  118  forms and inserts a watchdog setup call. As shown in  FIG. 2 , the compiler  118  forms the watchdog setup call  210  after parsing the watchdog specification  202  and forms the watchdog setup call  212  after parsing the watchdog specification  206 . Although the setup calls  210 - 212  (and additional calls explained below) are shown in  FIG. 2  as source code statements, it is noted that the compiler  118  typically instead inserts the calls directly into the object code  124  during compilation.  
         [0033]     As shown in  FIG. 2 , the watchdog setup calls  202 ,  212  are function calls to the wd_start_watchdog function in the watchdog support library  140 . The parameter and return type characteristics of the watchdog setup calls  202 ,  212  are shown below in Table 4.  
                         TABLE 4                           Parameters for wd_start_watchdog( )            Parameter   Explanation               wd_watchdog_t *watchdog   Pointer to a watchdog specifier structure           (type wd_watchdog_t)       Return type: wd_handle_t   A unique identifier for the code block           being watched by the watchdogs.                  
 
         [0034]     The compiler  118  parses the watchdog specifier  202  to generate parameters for the watchdog specifier structure passed to wd_start_watchdog( ). The elements of the watchdog specifier structure are shown below in Table 5:  
                         TABLE 5                           Parameters for the watchdog specifier structure            Parameter   Explanation               wd_handle_t event_handle   A unique identifier generated by the           watchdog setup call and represented,           for example, by an integer       wd_threat_type_t threat_type   A threat type represented, for           example, by an integer. The threat           type identifies whether the threat           posed by the code block is a failure           to progress threat (e.g., a hang) or a           failure that will abort the program.       wd_handler handler   A pointer to a function that should be           called when the watchdog detects a           problem.       void *handler_param   An opaque parameter passed to the           handler function for handling the           watchdog event.       int signal   An integer that represents the signal           number to raise when a watchdog           event occurs.       wd_heartbeat_interval   For a hang threat type,       heartbeat_interval   heartbeat_interval specifies how           often (for example, in microseconds)           to expect a message or signal from a           watchdog progress call.       float heartbeat_scale   This parameter specifies the units on           the heartbeat_interval parameter, in           seconds.       wd_max_heartbeats   For a threat type that is a hang,       max_heartbeats   max_heartbeats specifies how many           heartbeats would indicate that the           program has stopped making           progress (e.g., is in an infinite loop).       char *user_func_lib   A pointer to a string that holds the           pathname to a library that contains           the function specified by the ‘handler’           parameter.                  
 
         [0035]     In particular, the watchdog specifier  202  parameters map to the watchdog specifier structure in the following manner. The threat_type is obtained by determining whether ‘hang’ or ‘abort’ or both have been specified in the watchdog specification. The handler is specified by the watchdog specification by the ‘call’ parameter (and may be set to NULL if the signal parameter is non-zero), while the pointer to the handler parameters may be a pointer to any data or function that the handler may use while reacting to the watchdog event. The handler may be, for example, dynamically loadable code created by the user to handle aborts. As examples, the handler may be stored in a shared library on a UNIX machine or in a dynamically linked library (DLL) on a Microsoft Windows machine. The signal parameter is the signal number to be sent to the thread if the watchdog sees a problem, and may be set to zero if the thread_type is ‘abort’ or the ‘handler’ is not NULL.  
         [0036]     The parameters heartbeat_interval, max_heartbeats, and the pointer to the user function library are obtained directly from the watchdog specification. The heartbeat scale specifies the units on the heartbeat_interval in seconds. For example, heartbeat scale may be 0.001, or 1 millisecond. Then, a heartbeat_interval of 20 translates into an expected heartbeat every 20*0.001 seconds, or 20 milliseconds. The heartbeat scale may be, for example, a configurable parameter associated with the compiler  118 , or may be set forth in the watchdog specification. For example, the compiler  118  may interpret a heart_rate that is greater than zero as a multiplier for the heartbeat scale (e.g., as noted above 20 (the heart_rate) times 0.001 (the heartbeat scale)). A heart_rate less than zero may then be interpreted as including the heartbeat scale. For example, a heart_rate of 0.002 may specify a maximum time difference between watchdog updates of 2 milliseconds.  
         [0037]     The watchdog status table  138  may be, for example, a global table that holds, for each watchdog, a counter indicating the number of events for which the associated watchdog is watching and a thread or process id of the watchdog thread or program. The watchdog setup call maintains the watchdog status table  138 .  
         [0038]     As noted above, there are several actions that a watchdog can take when the event occurs for which it is watching. The actions include, as examples, calling a user-defined function and sending a signal to the thread in which the event occurs. In either case, the watchdog stops watching for that particular event and decrements the event count in the global table  138 . If the event count goes to zero, the watchdog may (but is not required to) terminate itself.  
         [0039]     For watchdogs that are supposed to call a user-defined function, there is generally one watchdog per watched thread. When an event occurs, the watchdog calls the user-defined function. If the user-defined function returns, the watchdog generally terminates itself (but not the process in which it is running) by terminating the thread in which it is running. The watchdog stores information about each monitored event in its parameter table (e.g., the parameter table  144 ) as shown in Table 6:  
                         TABLE 6                       Parameters stored in the watchdog parameter table                                a user handler specifier that identifies a   maximum number       user defined function to call when a   of heartbeats before       watchdog event occurs   assuming that a thread is hung       number of heartbeats recorded so far   maximum heartbeat interval       time of last contact   event handle                  
 
         [0040]     Each time a program reports progress to the watchdog, it increments the number of heartbeats recorded and then compares that number to the maximum number that would indicate a hung thread before deciding whether to continue. If a watchdog does not get a heartbeat within the time interval specified by the maximum heartbeat interval, then it assumes that the thread is hung. The event handle entry provides a handle that the watchdog uses to distinguish between multiple events for which it is watching.  
         [0041]     Watchdogs that have been specified to send a signal can watch many threads at once. Those watchdogs keep the following information for each event for which they are watching in their parameter table as shown in Table 7:  
                         TABLE 7                       Parameters stored in the watchdog parameter table                                signal to send   maximum number of heartbeats before           assuming that the thread is hung       number of heartbeats   maximum heartbeat interval       recorded so far       time of last contact   event handle       thread ID of the thread to watch                  
 
         [0042]     The thread ID allows the watchdog to identify and send the signal to the correct thread.  
         [0043]     The sets of entries in the parameter tables may be stored in a linked list, hash table, or any other data structure that allows read/write access to multiple records.  
         [0044]     After setting the parameters in the watchdog status table  138 , the watchdog setup call  210  initiates execution of a watchdog to watch the code block (and passes to the watchdog the parameters for its parameter table). The type of watchdog initiated depends in part of the threat scope. When the threat scope is thread-level (i.e., failure of the code block would cause failure of the thread including the code block), then the watchdog setup call  210  initiates execution of the watchdog thread  130  to monitor the code block. On the other hand, when the threat scope is program-level (i.e., failure of the code block would cause failure of the programs as a whole), then the watchdog setup call  210  initiates execution of the watchdog program  132  to monitor the program that includes the code block.  
         [0045]     It may also be the case that the threat scope is machine level (i.e., failure of the code block would cause the data processing system  100  to crash). In that case, the watchdog setup call  210  initiates execution of the watchdog program  134  on the separate data processing system  136 . To do so, the watchdog setup call  210  may, as examples, send a message to or invoke a remote procedure call on the data processing system  136 . The watchdog program  134  then monitors the data processing system  100  to determine is it is continuing to function. For example, watchdog progress calls, for a machine level threat scope, may send messages generated by watchdog progress and completion calls over the network to the data processing system  136  and the watchdog program  134  so that the watchdog program  134  receives a notification that the program is functioning correctly.  
         [0046]     Each watchdog, as explained above, determines its operating parameters from the watchdog status table  138 . A watchdog that checks for progress thus expects to receive heartbeat indicators at least as frequently as given by the heartbeat_interval parameter, and no more heartbeats than given by the max_heartbeats parameter. If either condition is violated (e.g., the maximum number of heartbeats is exceeded), then the watchdog initiates execution of the watchdog handler and passes a pointer to the handler parameters to the handler.  
         [0047]     The watchdog handler may, as examples, terminate the thread or program, generate a report or display that identifies the error, reboot a remote machine, store debugging information in a log file, and the like.  
         [0048]     Note that the watchdog setup call  210  returns an identification value to the calling program that identifies the watchdog configured to watch the code block. As shown in  FIG. 2 , the variable event_handle stores the value. Subsequent calls to watchdog functions generally include the identification value as a mechanism for identifying a specific watchdog.  
         [0049]     The watchdog progress call  214  provides a mechanism for reporting a program status to a watchdog. The program status, for example, may indicate that the program is continuing to execute instructions. In that regard, the watchdog progress call  214  provides a periodic heartbeat indicator to the watchdog identified by the event_handle parameter. Note that if the pointer assignment statement or function call do not execute properly, it is unlikely that the loop will return to the watchdog progress call  214 . Thus, after the heartbeat interval expires, the watchdog will invoke the watchdog handler to perform some remedial action. On the other hand, for example, if the pointers are circularly linked such that the loop would execute indefinitely, then the watchdog will receive more than the maximum number of heartbeats. Similarly, the watchdog will invoke the watchdog handler to perform some remedial action.  
         [0050]     With regard to the code block  204 , the compiler  118  inserts the watchdog progress call  214  into the code block  204  after the compiler  118  has identified the bounds of the loop for the code block  204 . The watchdog progress call  214  may be inserted before or after any statement in the loop. The compiler  118 , however, generally inserts the watchdog progress call  214  at the top of the loop (as shown in  FIG. 2 ). Note that for a non-loop code block (e.g., the code block  208 ), the compiler  118  may insert watchdog progress calls  218  before or after one or more of the statements that comprise the code block  208 .  
         [0051]      FIG. 2  also shows a watchdog completion calls  216  and  220 . The watchdog completion call  216 , for example, informs the watchdog identified by the event_handle parameter that the code block  204  has finished executing. In response, the number of events for which the watchdog is watching is decremented in the status table  138 .  
         [0052]     Table 8, below, provides a summary of the watchdog functions available in the watchdog library  140 .  
                         TABLE 8                           Watchdog Library            Function   Explanation               wd_event_handle_t   Initiate execution of the       wd_start_watchdog(wd_watchdog_t   watchdogs to check for problems       *watchdog)   as specified in the fields on           each watchdog specifier           structure.       int wd_done(wd_handle_t event)   Informs the watchdogs watching           for a particular event to           stop watching.       int wd_report_progress(wd_handle_t   Send a heartbeat for a particular       event)   failure-to-progress event.       wd_time_t wd_get_time_limits(   Get the time limits for a       wd_handlt_t event)   particular failure-to-           progress event.       int wd_set_time(wd_handlt_t event)   Set or reset the time limits for a           particular failure-to-           progress event.                  
 
         [0053]     Table 9 shows, for one implementation, the underlying data types for the data types discussed above.  
                         TABLE 9                           Data Types            Type   Underlying Type               wd_event_handle_t   long long       wd_threat_type_t   long long       wd_threat_scope_t   int       wd_handler   pointer to a function that accepts a           void *parameter       wd_heartbeat_interval   int       wd_max_heartbeats   long long       wd_time_t   a structure:           wd_time_t           {            wd_heartbeat_interval heartbeat_interval;            float heartbeat_scale;            long long max_heartbeats;           }       wd_watchdog_t   pointer to a watchdog specifier structure                  
 
         [0054]     Turning next to  FIG. 3 , that figure shows a flow diagram  300  of the steps taken by the wd_start_watchdog( ) function (the watchdog setup call) provided by the watchdog library  140 . The watchdog setup call extracts the watchdog parameters from the watchdog specifier (Step  302 ). The compiler determines the threat scope (Step  304 ). Depending on the threat scope, the watchdog setup call may initiate execution of a watchdog thread (Step  306 ), a watchdog program (Step  308 ), or a watchdog program on a separate data processing system (Step  310 ).  
         [0055]     In one embodiment, there will be one watchdog thread watching other threads. In other words, all threads that ask to be watched will be watched from the same thread. When a thread specifies its threat, the watchdog thread adds that threat and thread information noted above to its watchdog parameter table. Note that, in general, watchdog threads will be watching for hangs, because aborts will kill an entire process, including the watchdog thread.  
         [0056]     As explained above, the watchdog specification for a thread with a “hang” threat typically sets forth a heartbeat interval and a maximum number of heartbeats. The heartbeat interval is the maximum amount of time that the thread can go without issuing a heartbeat; if the watchdog does not hear a heartbeat within that time, the watchdog assumes that the thread is hung. If the thread does not want to issue heartbeats (i.e., the thread simply wants to give itself a certain amount of time to accomplish a task), the thread may set the maximum number of heartbeats to 1 and set the heartbeat interval to the amount of time the thread needs to complete its task. If the watchdog does not receive a heartbeat from the thread within that interval, the watchdog assumes that the thread is hung.  
         [0057]     The watchdog uses the heartbeat interval to determine when to wake up and check for problems. Ordinarily, the watchdog is asleep. If the watchdog is supposed to watch for a heartbeat from a particular thread every 10 time units, then the watchdog sets an alarm for itself to go off in 10 time units and goes to sleep. If the thread reports a heartbeat then the watchdog resets the alarm for another 10 time units.  
         [0058]     If the watchdog thread is watching multiple threads then the watchdog will set its alarm so that it wakes up in time to check for each expected heartbeat. As an example, if the watchdog thread is supposed to receive a heartbeat from thread A every 10 time units and thread B every 7 time units then the watchdog thread begins by setting the alarm for 7 time units and goes to sleep. Table 10 below shows an example of how events progress thereafter.  
                                     TABLE 10                       Time   Event   Comment                                0   Thread A starts   Set an alarm to wake up in 10 units (t = 10).       2   Thread B starts   Set an alarm to wake up in 7 units (t = 9).       6   Heartbeat A   Set an alarm to wake up in 3 units (t = 9) to               check on B; next check for A is at time 6               (now) plus 10 (heartbeat interval), or t = 16.       8   Hearbeat B   Set an alarm to wake up in 7 units (t = 15);               next check for B is 8 (now) plus 7 (hearbeat)               equals t = 15.       15   Wakeup due to   No heartbeat from B since time 8. Since           alarm set at time 8   more than time than the heartbeat_interval               has passed, the watchdog thread presumes               that thread B is hung.                  
 
         [0059]     Assuming that the action for thread B was to send a signal then the watchdog thread will send a signal to thread B. As an example, a watchdog thread running on a system that supports Posix threads can use pthread_kill to send the signal. If the action for B was to call a user-defined subroutine then the watchdog thread creates a thread that runs the user subroutine using, for example, pthread_create on a system that supports Posix threads.  
         [0060]     In either event, information about thread B is removed from the watchdog parameter table and the watchdog thread stops watching thread B. The next check on thread A (in the example above) is at t=16. Thus, the watchdog thread sets the alarm for t=16 and goes back to sleep.  
         [0061]      FIG. 4  shows a flow diagram  400  of the steps taken by the wd_done( ) function. The function updates the watchdog status table  138  to reflect completion of the code block being watched (Step  402 ). To that end, as examples, the function may remove the watchdog entry for the code block or set a ‘completed’ flag in the watchdog table  138 . The function may also generate an indication (e.g., a dialogue box, log entry, or the like) that the code block has successfully completed (Step  404 ). In addition, the function may also send a completion or termination message to the watchdog thread or program that is watching the code block (Step  406 ).  
         [0062]      FIG. 5  shows a flow diagram  500  of the steps taken by the wd_report_progress( ) function. The function is used as a reporting call to inform the watchdog that execution of code in the code block has reached the point where the wd_report_progress( ) function was inserted. The reporting call thus functions as a heartbeat to the watchdog. The function determines to which watchdog to send the heartbeat by checking the watchdog identifier passed to the reporting call (Step  502 ). The function then sends a heartbeat indicator to the watchdog (Step  504 ). As examples, the function may send a message or signal to the watchdog, set or reset a flag in the watchdog status table  138 , or the like.  
         [0063]      FIG. 6  shows a flow diagram  600  of the steps taken by the wd_get_time_limits( ) function. The function reads the watchdog identifier parameter (Step  602 ) and retrieves the corresponding heartbeat interval from the watchdog status table  138  (Step  604 ). The heartbeat interval is then returned to the calling program (Step  606 ).  
         [0064]      FIG. 7  shows a flow diagram  700  of the steps taken by the wd_set_time_limits( ) function. The function reads the watchdog identifier parameter and new heartbeat interval (Step  702 ) and sets the corresponding heartbeat interval from the watchdog status table  138  (Step  704 ).  
         [0065]      FIG. 8  shows a flow diagram  800  of the steps taken by a watchdog program or thread. The watchdog first checks the watchdog parameter table to determine which type watchdog event for which it is watching (Step  802 ).  
         [0066]     A progress watchdog determines (using the heartbeat parameters) when a program or thread is taking too long to compute a result or reach a specified execution point (for example, the program may be in an infinite loop) For that reason, the progress watchdog may first check the watchdog parameter table to ascertain the heartbeat interval and maximum number of heartbeats, as well as a maximum completion time limit (Step  804 ). If the code block that is being watched completes, then the watchdog generally terminates (Step  806 ). The watchdog may ascertain completion of the code block by receiving a signal or message (arising from the use of the wd_complete( ) function), or by checking for a flag in the watchdog parameter table  138  to be set or reset.  
         [0067]     If the code block has not completed, the progress watchdog determines whether the code block is making sufficient timely progress by checking to see if the code block has exceeded a specified time limit for completion, whether the code block exceeds the number of heartbeats to complete a particular operation, whether the heartbeat interval is greater than that specified for the code block, or whether the code block has not passed a particular checkpoint within a specified time limit (Step  808 ). If so, the watchdog determines the action for handling the watchdog event (see below).  
         [0068]     An abort watchdog determines when a program or thread has permanently terminated processing in a way that prevents the program or thread from continuing. To that end, the abort watchdog may set up a notification method (e.g., code to accept and process messages or signals) with which the operating system may communicate to send a notification that a program or thread has aborted, terminated, or crashed (Step  810 ). In a manner similar to that of the progress watchdog, the abort watchdog checks to see if the code block has completed (Step  812 ), and if so, generally terminates.  
         [0069]     In addition or in the alternative to the notification method, the abort watchdog may periodically test for the existence of the computational entity (e.g., the program or thread) that is executing the code block (Step  814 ). The abort watchdog may check for the existence of the program or thread, for example, by checking the processes that are running in the data processing system  100 . If the entity is no longer running (checked at step  816 ), then the abort watchdog determines the action for handling the watchdog event (see below).  
         [0070]     As noted above, the watchdog program may take remedial action by sending a signal to the program being watched (when the program has not aborted), or by invoking a handler. To that end, the watchdog program determines which action to take (Step  818 ). Generally, the remedial action is set forth in the watchdog specification. When the remedial action is to send a signal, then the watchdog program initiates a call to send the signal set forth in the watchdog specification to the program (Step  820 ). If the remedial action is to invoke a handler, then the watchdog program initiates execution of the handler identified in the watchdog specification (Step  822 ).  
         [0071]     The foregoing description of an implementation of the invention has been presented for purposes of illustration and description. It is not exhaustive and does not limit the invention to the precise form disclosed. Modifications and variations are possible in light of the above teachings or may be acquired from practicing of the invention. For example, the described implementation includes software but the present invention may be implemented as a combination of hardware and software or in hardware alone. Note also that the implementation may vary between systems. The invention may be implemented with both object-oriented and non-object-oriented programming systems. The claims and their equivalents define the scope of the invention.