Producer, consumer POSIX - c

Question

I am trying to write simple producer consumer app using C POSIX semaphores.
Consumer:
int memoryID;
struct wrapper *memory;
int main(int argc, char **argv) {
srand(time(NULL));
key_t sharedMemoryKey = ftok(".",MEMORY_KEY);
if(sharedMemoryKey==-1)
{
perror("ftok():");
exit(1);
}
memoryID=shmget(sharedMemoryKey,sizeof(struct wrapper),0);
if(memoryID==-1)
{
perror("shmget(): ");
exit(1);
}
memory = shmat(memoryID,NULL,0);
if(memory== (void*)-1)
{
perror("shmat():");
exit(1);
}
while(1)
{
int r = rand();
sem_wait(&memory->full);
sem_wait(&memory->mutex);
int n;
sem_getvalue(&memory->full,&n);
printf("Removed item: %d",(memory->array)[n]);
usleep(1000000);
sem_post(&memory->mutex);
sem_post(&memory->empty);
}
}
Producer:
int memoryID;
struct wrapper *memory;
int rc;
void atexit_function() {
rc = shmctl(memoryID, IPC_RMID, NULL);
rc = shmdt(memory);
}
int main(int argc, char **argv) {
atexit(atexit_function);
//creating key for shared memory
srand(time(NULL));
key_t sharedMemoryKey = ftok(".", MEMORY_KEY);
if (sharedMemoryKey == -1) {
perror("ftok():");
exit(1);
}
memoryID = shmget(sharedMemoryKey, sizeof(struct wrapper), IPC_CREAT | 0600);
if (memoryID == -1) {
perror("shmget():");
exit(1);
}
memory = shmat(memoryID, NULL, 0);
if (memory == (void *) -1) {
perror("shmat():");
exit(1);
}
//initialization
memset(&memory->array, 0, sizeof(memory->array));
sem_init(&memory->mutex, 1, 1);
sem_init(&memory->empty, 1, SIZE_OF_ARRAY);
sem_init(&memory->full, 1, 0);
if (memoryID == -1) {
perror("shmget(): ");
exit(1);
}
while(1)
{
int r = rand();
sem_wait(&memory->empty);
sem_wait(&memory->mutex);
int n;
sem_getvalue(&memory->full,&n);
printf("Adding task\t Value:%d\tNumber of tasks waiting:%d \n",r,n);
(memory->array)[n]=r;
usleep(1000000);
sem_post(&memory->mutex);
sem_post(&memory->full);
}
}
common.h:
#define MEMORY_KEY 5
#define SIZE_OF_ARRAY 10
struct wrapper
{
int array[SIZE_OF_ARRAY];
sem_t empty;
sem_t mutex;
sem_t full;
};
What is happening:
Producer is starting successfully
Producer is successfully adding elements to table and printing them out Quickly after starting producer,
I am starting consumer Consumer does not take element from
array even once
Producer fills up the array and is waiting
I do not really see where is the problem. I suspect that the problem is the implementation not the algorithm cause the algorithm is taken from wikipedia Link

Answer 1

Your consumer works fine. It's just not flushing to stdout. Do as nos suggested by putting a \n at the end of your consumer printf call. You can also see it working by just waiting longer. Your producer will start producing again after the consumer has executed a few iterations.