Programming

/*heres what the codes does... it spawns 3 new threads, so in all there r 4 threads. from 3 of the threads i send a message to the 4th thread, and i am using 1 message queue to hold msgs from different senders. using the type variable to distinduish the msgs.*/


#include<stdio.h>
#include<sys/types.h>
#include<sys/ipc.h>
#include<sys/msg.h>
#include<stdlib.h>
#include<errno.h>

//this is the structure used to hold the message 
struct message
{
        int type;
        int msg;
};
 
int main(void)
{
        pid_t pid0,pid1,pid_p,pid_c1,pid_c2,pid_c3;
        key_t key;
        int msgqid;
        
        struct message *msgs,*msgr;
        pid_p=getpid();
 
        //used to generate the key for msg queue
	if((key=ftok("abc.txt",'c'))==-1)
                perror("Error in ftok\n");
        else
                printf("Ftok executed.Key=%d\n",key);
 	
	//get the msg queue
        if((msgqid=(msgget(key,0666|IPC_CREAT))==-1))
                perror("Error creating queue\n");
        else
                printf("Queue created.MSGQID=%ld\n",msgqid);
 	
	//using the forks so that i have 4 separate threads
        pid0=fork();
        if(pid0<0)
        {
                perror("Error in fork\n");
        }
 
        pid1=fork();
        if(pid1<0)
        {
                perror("Error in fork\n");
        }
 
	/*checks pid as entry level condition. in each of the thread i set a different type
	  to distinguish between the messages.*/
        if(pid0==0 && pid1==0)
        {
                pid_c1=getpid();
                printf("In child.Process ID=%d\n",pid_c1);
                msgs->type=1;
                msgs->msg=1;
                if(msgsnd(msgqid,&(msgs->type),sizeof(struct message),1)==-1)
                {       printf("%d\n",errno);perror("Message not sent.Type 1\n");}
 
                else
                        printf("Message sent.Type 1\n");
        }
 
        if(pid0==0 && pid1!=0)
        {
                pid_c2=getpid();
                printf("In child.Process ID=%d\n",pid_c2);
                msgs->type=2;
                msgs->msg=2;
                if(msgsnd(msgqid,&(msgs->type),sizeof(struct message),2)==-1)
                        perror("Message not sent.Type 2\n");
                else
                        printf("Message sent.Type 2\n");
        }
 
        if(pid0!=0 && pid1==0)
        {
                pid_c3=getpid();
                printf("In child.Process ID=%d\n",pid_c3);
                msgs->type=3;
                msgs->msg=3;
                if(msgsnd(msgqid,&(msgs->type),sizeof(struct message),3)==-1)
                        perror("Message not sent.Type 3\n");
                else
                        printf("Message sent.Type 3\n");
        }
 

	//in the 4th thread i read the message from the message queue based on the type
        if(pid0!=0 && pid1!=0)
        {
                wait(NULL);
                wait(NULL);
                wait(NULL);
                printf("In parent.Process ID=%d\n",pid_p);
                                 
                if(msgrcv(msgqid,&(msgr->type),sizeof(struct message),1,0)==-1)
                        perror("Message not recvd.Type 1\n");
                else
                        printf("Message revcd.Type 1\n");
 
                if(msgrcv(msgqid,&(msgr->type),sizeof(struct message),2,0)==-1)
                        perror("Message not recvd.Type 2\n");
                else
                        printf("Message revcd.Type 2\n");
 
                if(msgrcv(msgqid,&(msgr->type),sizeof(struct message),3,0)==-1)
                        perror("Message not recvd.Type 3\n");
                else
                        printf("Message revcd.Type 3\n");
 
		//destroying the queue

                if(msgctl(msgqid,IPC_RMID,NULL)==-1)
                        perror("Error removing queue\n");
                else
                        printf("Queue removed\n");
        }
 
        exit(0);
}