91 lines
2.4 KiB
C
91 lines
2.4 KiB
C
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/* This file is part of the sample code and exercises
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* used by the class "Advanced Programming in the UNIX
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* Environment" taught by Jan Schaumann
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* <jschauma@netmeister.org> at Stevens Institute of
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* Technology.
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*
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* This file is in the public domain.
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*
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* You don't have to, but if you feel like
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* acknowledging where you got this code, you may
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* reference me by name, email address, or point
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* people to the course website:
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* https://stevens.netmeister.org/631/
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*/
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/* A simple example of IPC using a pipe(2). This may
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* be compared to
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*
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* echo msg | cat
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*
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* but we display information in each process about
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* its pid and ppid.
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*
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* Depending on the order in which the parent and
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* child end up running, the child may report a ppid
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* of '1': if the parent has exited before the child
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* has finished reading data, then init(8) will have
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* reaped (and possibly reparented) it.
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*/
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#include <sys/wait.h>
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#include <err.h>
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#include <errno.h>
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#include <stdio.h>
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#include <stdlib.h>
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#include <string.h>
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#include <unistd.h>
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int
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main() {
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int n, r, fd[2];
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pid_t pid;
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char line[BUFSIZ];
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if (pipe(fd) < 0) {
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err(EXIT_FAILURE, "pipe");
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/* NOTREACHED */
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}
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if ((pid = fork()) < 0) {
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err(EXIT_FAILURE, "fork");
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/* NOTREACHED */
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} else if (pid > 0) {
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/* The parent closes the read-end of
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* the pipe, since it only writes data
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* to the child. */
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(void)close(fd[0]);
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(void)printf("P=> Parent process with pid %d (and its ppid %d).\n",
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getpid(), getppid());
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(void)printf("P=> Sending a message to the child process (pid %d).\n", pid);
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(void)snprintf(line, BUFSIZ, "Hello child! I'm your parent, pid %d!\n",
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getpid());
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if ((r = write(fd[1], line, strlen(line))) < 0) {
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(void)fprintf(stderr, "Unable to write to pipe: %s\n",
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strerror(errno));
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}
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(void)close(fd[1]);
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} else {
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/* The child process closes the write
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* end of the pipe, since it only
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* plans on reading. */
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(void)close(fd[1]);
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(void)printf("C=> Child process with pid %d (and its ppid %d).\n",
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getpid(), getppid());
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(void)printf("C=> Reading a message from the parent (pid %d):\n",
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getppid());
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if ((n = read(fd[0], line, BUFSIZ)) < 0) {
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(void)fprintf(stderr, "Unable to read from pipe: %s\n",
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strerror(errno));
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} else if ((r = write(STDOUT_FILENO, line, n)) < 0) {
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(void)fprintf(stderr, "Unable to write to pipe: %s\n",
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strerror(errno));
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}
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(void)close(fd[0]);
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}
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(void)wait(NULL);
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return EXIT_SUCCESS;
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}
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