Message Queue is a queue of messages used for InterProcess communication, which is stored within the kernel and identified by a message queue identifier.

The following code is an implementation of message queue. Two source files, msgQ_write.c and msgQ_read.c, need to be created.

//msgQ_write.c

// C Program for Message Queue (Writer Process)

#include

#include

#include

#define MAX 10

// structure for message queue

struct mesg_buffer {

long mesg_type;

char mesg_text[100];

} message;

int main()

{

key_t key;

int msgid;

// ftok to generate unique key

key = ftok("progfile", 65);

// msgget creates a message queue

// and returns identifier

msgid = msgget(key, 0666 | IPC_CREAT);

message.mesg_type = 1;

printf("Write Data : ");

fgets(message.mesg_text,MAX,stdin);

// msgsnd to send message

msgsnd(msgid, &message, sizeof(message), 0);

// display the message

printf("Data send is : %s ", message.mesg_text);

return 0;

}

//msgQ_read.c

// C Program for Message Queue (Reader Process)

#include

#include

#include

// structure for message queue

struct mesg_buffer {

long mesg_type;

char mesg_text[100];

} message;

int main()

{

key_t key;

int msgid;

// ftok to generate unique key

key = ftok("progfile", 65);

// msgget creates a message queue

// and returns identifier

msgid = msgget(key, 0666 | IPC_CREAT);

// msgrcv to receive message

msgrcv(msgid, &message, sizeof(message), 1, 0);

// display the message

printf("Data Received is : %s ",

message.mesg_text);

// to destroy the message queue

msgctl(msgid, IPC_RMID, NULL);

return 0;

}

System calls used for message queues:

ftok(): is use to generate a unique key.

msgget(): either returns the message queue identifier for a newly created message queue or returns the identifiers for a queue which exists with the same key value.

msgsnd(): Data is placed on to a message queue by calling msgsnd().

msgrcv(): messages are retrieved from a queue.

msgctl(): It performs various operations on a queue. Generally it is use to destroy message queue.

1a) Please compile them using gcc sourcecode -o output. Run them respectively. Is it successful?

1b) Run msgQ_write.out three times with different inputs. And run msgQ_read.out twice. What are the results? Please paste the screenshots and explain why?