/*q.h*/
#ifndef Q_H
	#define Q_H
	#define QKEY ftok("q.h",1)
	#define MSGSZ 128

	#ifdef DEBUG
		#define DEBUG_PRINT(...) fprintf(stderr,__VA_ARGS__)
		/* this __VA_ARGS__ thing allows a macro to
		take a varialble number of arguments */
	#else
		#define DEBUG_PRINT(...) /* __VA_ARGS__ */
	#endif

	int init_queue();
	int exchange_pids();
	void remove_queue();
	int send_mesg(char*,int);
	int send_mesg_signal(char*,int);
	int recv_mesg(char*,int);
#endif



/*signalmsg.c*/
#include<signal.h>
#include<string.h>
#include<stdlib.h>
#include<stdio.h>
#include<unistd.h>
#include<errno.h>
#include"q.c"
#include"q.h"

int cnt;
void hndlr(int);

main()
{
        struct sigaction buf;
        char msg[MSGSZ];
        int stop=0,n;
        sigfillset(&buf.sa_mask);
        buf.sa_flags=0;
        buf.sa_handler=hndlr;
        sigaction(SIGUSR1,&buf,NULL);
        sigaction(SIGINT,&buf,NULL);
        init_queue();
        exchange_pids();
        
while(!stop)
        {
                printf("\nEnter message: ");
                while (-1 == (n=read(0,msg,MSGSZ-1) ))
                {
                        if (errno != EINTR )
                        {
                           perror("read");
                           send_mesg("bye\n",0);
                           exit(1);
                        }
                        for(;cnt>0;cnt--)
                        {
                           recv_mesg(msg,0);
                           printf("\nReceived Message: %s\n", msg);
                           if (0==strcmp(msg,"bye\n"))
                           {
                                remove_queue();
                                exit(0);
                           }
                        }
                        printf("\nEnter message: ");
                }
                msg[n]=0;
                send_mesg_signal(msg,0);
                if (0==strcmp(msg,"bye\n"))
                        stop=1;
        }
        return 0;
}

void hndlr(int sig)
{
        DEBUG_PRINT("Caught signal: %d\n",sig);
        switch(sig)
        {
        case SIGUSR1:   DEBUG_PRINT("USR1 branch\n");
                        cnt++;
                        break;
        case SIGINT:    DEBUG_PRINT("SIGINT branch\n");
                        send_mesg_signal("bye\n",0);
                        exit(0);
                        break;
        default:        fprintf(stderr,"Yikes how did I get here?!!!\n");
                        exit(1);
        }

}



/*q.c*/
#include<stdio.h>
#include<sys/types.h>
#include<sys/ipc.h>
#include<sys/msg.h>
#include<unistd.h>
#include<signal.h>
#include<errno.h>
#include"q.h"

struct mymsg
{
        long mtype;
        char mtext[MSGSZ];
};

static int qid;
static int channel_no;
static pid_t remote_pid;

void remove_queue()
{
        msgctl(qid,IPC_RMID,0);
}

int init_queue()
{
        char  msg[MSGSZ];
        int rv;
        if( -1 != ( qid = msgget(QKEY,IPC_CREAT|IPC_EXCL|0600) ))
        {
                /* am entity A using channel 1 */
                channel_no=1;
                DEBUG_PRINT("Am entity A\n");
                return 0;
        }
        if ( errno != EEXIST )
        {
                perror("MSGGET:");
                return -1;
        }
        if (-1 != ( qid = msgget(QKEY,IPC_CREAT|0600) ))
        {
                /* am entity B using channel 2 */
                 channel_no=2;
                DEBUG_PRINT("Am entity B\n");
                return 0;
        }

        perror("MSGGET:");
        return -1;
}

int exchange_pids()
{
        char msg[MSGSZ];
        if(channel_no==1)
        {
                /* sending PID to other end */
                sprintf(msg,"%d",getpid());
                send_mesg(msg,0);
                DEBUG_PRINT("My pid is %s\n",msg);
                /* grab pid from other end */
                recv_mesg(msg,0);
                sscanf(msg,"%d",&remote_pid); 
                DEBUG_PRINT("Received PID is %s\n",msg);
        }
        else
        {
                /* grab pid from other end */
                recv_mesg(msg,0);
                sscanf(msg,"%d",&remote_pid);
                DEBUG_PRINT("Received PID is %s\n",msg);
                
                /* sending PID to other end */
                sprintf(msg,"%d",getpid());
                send_mesg(msg,0);
                DEBUG_PRINT("My pid is %s\n",msg);
        }
        return remote_pid;
}

int recv_mesg(char *msg, int nb)
{
        struct mymsg m;
        int options=0,len;
        int recv=((channel_no==1)?2:1);
        DEBUG_PRINT("Receiving on %d\n",recv);
        if (nb) options|=IPC_NOWAIT;
        if( -1==(len=msgrcv(qid,&m,MSGSZ,recv,options)))
                return -1;
        strcpy(msg,m.mtext);
        return len;
}

int send_mesg(char* msg,int nb)
{
        struct mymsg m;
        int options,len;
        m.mtype=channel_no;
        strcpy(m.mtext,msg);
        len=strlen(msg)+1;
        options=0;
        if (nb) options|=IPC_NOWAIT;
        DEBUG_PRINT("Sending type %d\n",m.mtype);
        return msgsnd(qid,&m,len,options);
}

int send_mesg_signal(char*msg,int nb)
{
        int rv;

        rv=send_mesg(msg,nb);
        kill(remote_pid,SIGUSR1);
        return rv;
}