procexec/multi_wait.c

This is procexec/multi_wait.c (Listing 26-1, page 543), an example from the book, The Linux Programming Interface.

The source code file is copyright 2022, Michael Kerrisk, and is licensed under the GNU General Public License, version 3.

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/* 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);
    }
}

 

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