procexec/multi_wait.c

+/* multi_wait.c
+
+   Demonstrate the use of wait(2): create multiple children and then wait
+   for them all.
+
+   Usage: multi_wait sleep-time...
+
+   One child process is created for each command-line argument. Each child
+   sleeps for the number of seconds specified in the corresponding command-line
+   argument before exiting. After all children have been created, the parent
+   loops, waiting for terminated children, and displaying their PIDs.
+*/
 #include <sys/wait.h>
 #include <time.h>
 #include "curr_time.h"              /* Declaration of currTime() */
 #include "tlpi_hdr.h"
 
 int
 main(int argc, char *argv[])
 {
     int numDead;       /* Number of children so far waited for */
     pid_t childPid;    /* PID of waited for child */
     int j;
 
     if (argc < 2 || strcmp(argv[1], "--help") == 0)
         usageErr("%s sleep-time...\n", argv[0]);
 
     setbuf(stdout, NULL);           /* Disable buffering of stdout */
 
     for (j = 1; j < argc; j++) {    /* Create one child for each argument */
         switch (fork()) {
         case -1:
             errExit("fork");
 
         case 0:                     /* Child sleeps for a while then exits */
             printf("[%s] child %d started with PID %ld, sleeping %s "
                     "seconds\n", currTime("%T"), j, (long) getpid(),
                     argv[j]);
             sleep(getInt(argv[j], GN_NONNEG, "sleep-time"));
             _exit(EXIT_SUCCESS);
 
         default:                    /* Parent just continues around loop */
             break;
         }
     }
 
     numDead = 0;
     for (;;) {                      /* Parent waits for each child to exit */
         childPid = wait(NULL);
         if (childPid == -1) {
             if (errno == ECHILD) {
                 printf("No more children - bye!\n");
                 exit(EXIT_SUCCESS);
             } else {                /* Some other (unexpected) error */
                 errExit("wait");
             }
         }
 
         numDead++;
         printf("[%s] wait() returned child PID %ld (numDead=%d)\n",
                 currTime("%T"), (long) childPid, numDead);
     }
 }