program..

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

#define QKEY		(key_t) 0111
#define QPERM		0660
#define MAXOBN		50
#define MAXPRIOR	10

struct q_entry{
	long mtype;
	char mtext[MAXOBN+1];
};

int init_queue(void) {
	int queue_id;

	if ((queue_id=msgget(QKEY, IPC_CREAT|QPERM))==-1)
		printf("msgget failed\n");
	return(queue_id);
}

int serve(void) {
	int mlen, r_qid;
	struct q_entry r_entry;

	if ((r_qid=init_queue())==-1)
		return(-1);

	for (;;) {
		if ((mlen=msgrcv(r_qid, &r_entry, MAXOBN, (-1*MAXPRIOR), MSG_NOERROR)) == -1) {
			printf("msgrcv failed\n");
			return(-1);
		}
		else {
			r_entry.mtext[mlen]='\0';
			printf("\n priority : %ld name: %s\n", r_entry.mtype, r_entry.mtext);
		}
	}
}

main(){

	serve();

	exit(0);
}

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

#define QKEY		(key_t) 0111
#define QPERM		0660
#define MAXOBN		50
#define MAXPRIOR	10

struct q_entry{
	long mtype;
	char mtext[MAXOBN+1];
};

int init_queue(void) {
	int queue_id;

	if ((queue_id=msgget(QKEY, IPC_CREAT|QPERM))==-1)
		printf("msgget failed\n");
	return(queue_id);
}

int enter(char *objname, int priority) {
	int len, s_qid;
	struct q_entry s_entry;

	if ((len=strlen(objname)) > MAXOBN) {
		printf("name too long\n");
		return(-1);
	}
	if (priority > MAXPRIOR || priority <= 0) {
		printf("invalid priority lavel\n");
		return(-1);
	}	
	if ((s_qid=init_queue())==-1)
		return(-1);
	s_entry.mtype =(long)priority;
	strncpy (s_entry.mtext, objname, MAXOBN);
	if (msgsnd(s_qid, &s_entry, len, 0)==-1) {
		printf("msgsnd faild\n");
		return(-1);
	}
	else
		return(0);
}

main(int argc, char **argv){
	int i;

	for (i=1; i<argc; i++)
		enter(argv[i], argc-i);

	exit(0);
}

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

#define QKEY		(key_t) 0111
#define QPERM		0660

struct q_entry{
	long mtype;
	int data;
};

int init_queue(void) {
	int queue_id;

	queue_id=msgget(QKEY, IPC_CREAT|QPERM);
	return(queue_id);
}

int serve(void) {
	int r_qid;
	struct q_entry r_entry;

	r_qid=init_queue();

	for (;;) {
		msgrcv(r_qid, &r_entry, sizeof(int), 0, 0);
		printf("\n priority : %ld name: %d\n", r_entry.mtype, r_entry.data);
	}
}

main(){

	serve();
	exit(0);
}

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

#define QKEY		(key_t) 0111
#define QPERM		0660

struct q_entry{
	long mtype;
	int data;
};

int init_queue(void) {
	int queue_id;

	queue_id=msgget(QKEY, IPC_CREAT|QPERM);
	return(queue_id);
}

int enter(int data, int priority) {
	int s_qid;
	struct q_entry s_entry;

	s_qid=init_queue();
	s_entry.mtype =(long)priority;
	s_entry.data=data;
	msgsnd(s_qid, &s_entry, sizeof(int), 0);
	return(0);
}

main(){
	int i, data;

	for (i=0; i<3; i++){
		scanf("%d", &data);
		enter(data, i+1);
	}

	exit(0);
}

#include <sys/types.h>
#include <sys/ipc.h>
#include <sys/sem.h>
#include <errno.h>

#define SEMPERM 0600

union semun{
	int val;
	struct semid_ds *buf;
	ushort *array;
};

main() {
	int status=0, semid;
	union semun arg;

	if ((semid=semget((key_t) 0123, 1, SEMPERM|IPC_CREAT|IPC_EXCL))==-1) {
		if (errno==EEXIST)
			semid=semget((key_t) 0123, 1, 0);	
	}
	else {	
		arg.val=1;
		status=semctl(semid, 0, SETVAL, arg);	
	}
	if (semid==-1 || status==-1) {
		perror("initsem failed");
		exit (1);		
	}
	exit(0);
}

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

#define SEMPERM 0600

union semun{
	int val;
	struct semid_ds *buf;
	ushort *array;
};

int initsem(key_t semkey) {
	int status=0, semid;

	if ((semid=semget(semkey, 1, SEMPERM|IPC_CREAT|IPC_EXCL))==-1) {
		if (errno==EEXIST)
			semid=semget(semkey, 1, 0);	
	}
	else {	
		union semun arg;

		arg.val=1;
		status=semctl(semid, 0, SETVAL, arg);	
	}

	if (semid==-1 || status==-1) {
		perror("iniitsem failed");
		return (-1);		
	}

	return (semid);
}


int p(int semid) {
	struct sembuf p_buf;
	
	p_buf.sem_num=0;
	p_buf.sem_op=-1;
	p_buf.sem_flg=SEM_UNDO;

	if (semop(semid, &p_buf, 1) ==-1) {
		printf("p(semid) failed");
		exit(1);
	}

	return(0);
}

int v(int semid) {
	struct sembuf v_buf;
	
	v_buf.sem_num=0;
	v_buf.sem_op=1;
	v_buf.sem_flg=SEM_UNDO;

	if (semop(semid, &v_buf, 1) ==-1) {
		printf("v(semid) failed");
		exit(1);
	}

	return(0);
}

void handlesem(key_t skey);

main(){
	int i;
	key_t 	semkey=0x111;

	for (i=0; i<3; i++) {
		if (fork()==0)
			handlesem(semkey); 
	}

	for (i=0; i<3; i++) 
		wait(0);

	exit(0);
}

void handlesem(key_t skey) {
	int 	semid;
	pid_t 	pid=getpid();

	if ((semid=initsem(skey)) < 0)
		exit(1);

	printf("process %d before critical section\n", pid);
	p(semid);
	printf("process %d in critical section\n", pid);
	sleep(10);
	printf("process %d leaving critical section\n", pid);
	v(semid);
	printf("process %d exiting\n", pid);
	exit(0);
}