Guardian Programmer's Guide

Fault-Tolerant Programming in C
Guardian Programmer’s Guide — 421922-014
27 - 60
Primary and Backup Processing
process, then calls primary_processing. If it is the backup process, it calls
backup_processing.
Function primary_processing
Function primary_processing does the work of the application (which, in this case,
is to execute a loop that reads numbers from an input file and writes the numbers to an
output file and to the standard output). Within the loop, function update_backup is
called to send file state information to the backup process. If an end-of-file is
encountered in the input file, primary_processing stops the backup process and
returns to the main function. Function primary_processing is as follows:
/*This function performs the real work of the application. It
consists of a loop that reads lines from an input file and
writes them to an output file.*/
void primary_processing (void)
{
short counter;
char string_pointer[10];
for (;;)
{
/*Terminate immediately if end of file*/
if (fgets (string_pointer, 10, infile) == NULL)
exit (0); /*Stops primary and backup processes*/
counter = atoi(string_pointer);
(void) printf ("counter = %d\n", counter);
(void) fprintf (outfile, "%d\n", counter);
fflush (outfile);
update_backup ();
}
}
Function backup_processing
Function backup_processing handles the backup tasks, which include:
• Open $RECEIVE so that the backup process can receive messages from the
primary process and the operating system.
• Call MONITORCPUS to indicate to the operating system that the backup process
is to be notified if the primary process CPU fails.
• Enter an infinite loop that reads and processes messages from $RECEIVE.
If the backup process receives a message indicating that the primary process or CPU
has failed, it does the following:
• Creates and starts a new backup process.
• Calls primary_processing to continue application processing.