82 lines
1.9 KiB
C
82 lines
1.9 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 program to illustrate the use of Message
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* Queues.
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*
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* Note that message queues continue to exist after
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* all processes have terminated; messages continue to
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* remain in the queues as well. This is desired, but
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* requires that processes clean up after themselves
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* when they are done using the queues.
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*
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* Note that in this example we manually specify the
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* key instead of using ftok(2).
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*
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* Use msgsend.c to create/send messages, then run
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* this tool to retrieve them (in order). Note that
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* msgrecv will block if no messages are in the queue.
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*
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* Use ipcs(1) to inspect the usage.
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*
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* Derived from:
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* https://users.cs.cf.ac.uk/Dave.Marshall/C/node25.html
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*/
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#include <sys/ipc.h>
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#include <sys/msg.h>
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#include <sys/types.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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#define MSGSZ 128
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typedef struct msgbuf {
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long mtype;
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char mtext[MSGSZ];
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} message_buf;
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int
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main(int argc, char **argv) {
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int msqid;
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key_t key;
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message_buf rbuf;
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if (argc != 2) {
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(void)fprintf(stderr, "Usage: msgrecv key\n");
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exit(EXIT_FAILURE);
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}
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if ((key = atoi(argv[1])) < 1) {
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(void)fprintf(stderr, "Invalid key: %s\n", argv[1]);
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exit(EXIT_FAILURE);
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}
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if ((msqid = msgget(key, 0)) < 0) {
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perror("msgget");
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exit(EXIT_FAILURE);
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}
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if (msgrcv(msqid, &rbuf, MSGSZ, 1, 0) < 0) {
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perror("msgrcv");
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exit(EXIT_FAILURE);
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}
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(void)printf("%s\n", rbuf.mtext);
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exit(EXIT_SUCCESS);
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}
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