72 lines
1.7 KiB
C
72 lines
1.7 KiB
C
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// System V message queues: writes to a a message queue, sends
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// receives a response.
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//
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// Based on: http://beej.us/guide/bgipc/output/html/multipage/mq.html
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#include <stdio.h>
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#include <stdlib.h>
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#include <errno.h>
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#include <string.h>
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#include <sys/types.h>
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#include <sys/ipc.h>
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#include <sys/msg.h>
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// Custom struct to hold messages in the message queue
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struct my_msgbuf {
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long mtype; // tag allowing filtering of messages
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char mtext[200]; // Contents of message
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};
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int main(){
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// Get a unique IPC key based on a file name
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key_t key = ftok("kirk.c", 'B');
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if(key == -1){
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perror("ftok");
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exit(1);
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}
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// Get a message queue based on the key provided
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int msqid = msgget(key, 0644 | IPC_CREAT);
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if(msqid == -1) {
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perror("msgget");
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exit(1);
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}
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struct my_msgbuf buf;
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buf.mtype = 1; // all messages have the same tag, no filtering done in this program
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printf("Enter lines of text, ^D to quit:\n");
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// Repeatedly read a line of text into the message buffer and put it into the queue
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while(fgets(buf.mtext, sizeof(buf.mtext), stdin) != NULL) {
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int len = strlen(buf.mtext);
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// ditch newline at end, if it exists
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if (buf.mtext[len-1] == '\n'){
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buf.mtext[len-1] = '\0';
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}
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int sent = msgsnd(msqid, &buf, len+1, 0);
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if (sent == -1){
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perror("msgsnd");
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}
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// Expect an acknowledgement
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int received = msgrcv(msqid, &buf, sizeof buf.mtext, 0, 0);
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if (received == -1) {
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perror("msgrcv");
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exit(1);
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}
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printf("Got back: %s\n",buf.mtext);
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}
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// Eliminate the message queue
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int removal = msgctl(msqid, IPC_RMID, NULL);
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if (removal == -1) {
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perror("msgctl");
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exit(1);
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}
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return 0;
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}
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