74 lines
2.0 KiB
C
74 lines
2.0 KiB
C
/*
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* ipcmsg1.c - Using a message queue to send data from
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* a parent process to a child process
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* NOTE: message queues are persistent
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*/
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#include <mqueue.h> // needed for mq system calls
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#include <stdio.h> // needed for printf, perror
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#include <stdlib.h> // needed for exit
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#include <string.h> // needed for strcpy
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#include <sys/types.h> // needed for pid_t
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#include <sys/wait.h> // needed for wait system call
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#include <unistd.h> // needed for fork system call
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/* Struct for the queue message */
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typedef struct message
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{
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int message_id;
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char string[10];
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} message;
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int main()
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{
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// Create attributes for new queue
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struct mq_attr queue_attr;
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queue_attr.mq_flags = 0; // Ignored by kernel
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queue_attr.mq_maxmsg = 10; // Max messages the queue supports
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queue_attr.mq_msgsize = sizeof(message);
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queue_attr.mq_curmsgs = 0; // Not used
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// Create and open a queue
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mqd_t mqdes = mq_open("/CS3841QUEUE", O_RDWR | O_CREAT, S_IRUSR | S_IWUSR, &queue_attr);
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if (mqdes == -1)
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{
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printf("COULD NOT OPEN QUEUE\n");
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exit(EXIT_FAILURE);
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}
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pid_t pid = fork(); // fork into 2 processes
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if (pid < 0) // error
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{
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perror("fork");
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exit(EXIT_FAILURE);
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}
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else if (pid == 0) // child
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{
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// Child receives message from parent
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message from_parent;
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mq_receive(mqdes, (char *)&from_parent, sizeof(message), NULL);
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printf("Child got %d: %s from parent\n", from_parent.message_id, from_parent.string);
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// Close the queue
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mq_close(mqdes);
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return 0; // Return success
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}
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else // parent
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{
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// Parent sends message to child
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message to_child;
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to_child.message_id = 10;
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strcpy(to_child.string, "HELLO");
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mq_send(mqdes, (char *)&to_child, sizeof(message), 0);
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// Wait for child
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wait(0);
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// Close the queue
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mq_close(mqdes);
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}
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return 0; // Return success
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}
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