62 lines
1.5 KiB
C
62 lines
1.5 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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/* This program illustrates two things:
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* - the fact that after a fork both parent and child are (mostly)
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* identical; that is, the printf(3) buffer, if not yet flushed, is
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* copied into the child
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* - the difference between unbuffered and buffered I/O
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*
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* Illustrate by running twice, once with stdout connected to a terminal
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* (line-buffered) and once to a pipe or a file.
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*/
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#include <err.h>
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#include <stdio.h>
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#include <stdlib.h>
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#include <unistd.h>
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int global = 0;
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char buf[] = "a write to stdout\n";
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int
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main() {
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int local;
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pid_t pid;
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local = 1;
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if (write(STDOUT_FILENO, buf, sizeof(buf)-1) != sizeof(buf)-1) {
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err(EXIT_FAILURE, "write error");
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/* NOTREACHED */
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}
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(void)printf("before fork\n");
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if ((pid = fork()) < 0) {
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err(EXIT_FAILURE, "fork error");
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/* NOTREACHED */
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} else if (pid == 0) { /* child */
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global++;
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local++;
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} else { /* parent */
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sleep(1);
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global--;
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local--;
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}
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(void)printf("pid = %d, ppid = %d, global = %d, local = %d\n",
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getpid(), getppid(), global, local);
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return EXIT_SUCCESS;
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}
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