procexec/child_status.c

+/* child_status.c
+
+   Demonstrate the use of wait() and the W* macros for analyzing the child
+   status returned by wait()
+
+   Usage: child_status [exit-status]
+
+   If "exit-status" is supplied, then the child immediately exits with this
+   status. If no command-line argument is supplied then the child loops waiting
+   for signals that either cause it to stop or to terminate - both conditions
+   can be detected and differentiated by the parent. The parent process
+   repeatedly waits on the child until it detects that the child either exited
+   normally or was killed by a signal.
+*/
 #include <sys/wait.h>
 #include "print_wait_status.h"          /* Declares printWaitStatus() */
 #include "tlpi_hdr.h"
 
 int
 main(int argc, char *argv[])
 {
     int status;
     pid_t childPid;
 
     if (argc > 1 && strcmp(argv[1], "--help") == 0)
         usageErr("%s [exit-status]\n", argv[0]);
 
     switch (fork()) {
     case -1: errExit("fork");
 
     case 0:             /* Child: either exits immediately with given
                            status or loops waiting for signals */
         printf("Child started with PID = %ld\n", (long) getpid());
         if (argc > 1)                   /* Status supplied on command line? */
             exit(getInt(argv[1], 0, "exit-status"));
         else                            /* Otherwise, wait for signals */
             for (;;)
                 pause();
         exit(EXIT_FAILURE);             /* Not reached, but good practice */
 
     default:            /* Parent: repeatedly wait on child until it
                            either exits or is terminated by a signal */
         for (;;) {
             childPid = waitpid(-1, &status, WUNTRACED
 #ifdef WCONTINUED       /* Not present on older versions of Linux */
                                                 | WCONTINUED
 #endif
                     );
             if (childPid == -1)
                 errExit("waitpid");
 
             /* Print status in hex, and as separate decimal bytes */
 
             printf("waitpid() returned: PID=%ld; status=0x%04x (%d,%d)\n",
                     (long) childPid,
                     (unsigned int) status, status >> 8, status & 0xff);
             printWaitStatus(NULL, status);
 
             if (WIFEXITED(status) || WIFSIGNALED(status))
                 exit(EXIT_SUCCESS);
         }
     }
 }