Thread: Ipc

**Rhidian** · 03-23-2005

I am having difficulty with my IPC producer consumer program.

Code:

if ((shmid=shmget(KEY, sizeof(struct shseg), IPC_CREAT|0666|IPC_EXCL ==-1){
	 	if (errno==EEXIST) {
                 }
}

This code checks too see if the shared memory segment is in exclusive mode, if it is it should return the EEXIST error. Not sure if my syntax is correct in the if statment as it seems to create error not seen in the program without it.

Code:

int simshm(void)        {
        int shmid;
	int mutex,uflo,oflo;
      	shmid=shmget(KEY, sizeof(struct shseg), IPC_CREAT|0666); 
        ashseg=(struct shseg *) shmat(shmid, 0, 0); // follow initsem logic
	mutex=initsem(MUTEX,1);
	oflo=initsem(OFLO, 3);
	uflo=initsem(UFLO,0);
	printf("%d %d %d\n", mutex,oflo,uflo);
	while (1) {
		p(uflo);
		p(mutex);
		printf("con in\n");
		printf("con: %c\n",ashseg->buffer[ashseg->out]);
		ashseg->out=(ashseg->out + 1) % BUFSIZE; 
		v(mutex);
		v(oflo);
		printf("con out\n");
		sleep(1);
	
	}
        return 1;
                }

**Salem** · 03-23-2005

It's really hard to tell because
1. you don't post enough code
2. the code which you have posted doesn't compile.

**Rhidian** · 03-24-2005

Code:

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

#include <errno.h>
extern errno;

#define SEMPERM 0600


//initshm();

int initsem(key_t semkey,int semval)
	{
	int status=0, semid;
	if ((semid=semget(semkey,1,SEMPERM|IPC_CREAT|IPC_EXCL))==-1) {
		if (errno==EEXIST){
			semid=semget(semkey,1,0);
				return(semid);}
		}
	status=semctl(semid,0,SETVAL,semval);
	printf("initialising\n");
	if (semid==-1||status==-1) {
		perror("initsem failed\n");
		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) {
		perror("p(semid) failed\n");
		exit(1);
		}
	else
		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) {
		perror("v(semid) failedi\n");
		exit(1);
		}
	else
		return(0);
	}

int killsem(key_t semkey)
	{
	if (semctl(semkey,0,IPC_RMID,0)==-1)
		return(-1);
	return(0);
	}

/*test program for semaphore operations*/


This should be compiled with intial code i.e. gcc #name #name

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