Slow pthread consumer - c

Question

I've implemented a solution the producer / consumer problem in C using pthreads and semaphores.
My main thread is the producer and I launch N consumer threads.
My code is:
typedef struct
{
int buf[BUFSIZE]; /* shared var */
int in; /* buf[in%BUFSIZE] is the first empty slot */
int out; /* buf[out%BUFSIZE] is the first full slot */
sem_t full; /* keep track of the number of full spots */
sem_t empty; /* keep track of the number of empty spots */
pthread_mutex_t mutex; /* enforce mutual exclusion to shared data */
} CONSUMER_STRUCT;
CONSUMER_STRUCT shared;
This is the code for each of my consumer threads:
void *Consumer(void *arg)
{
int fd, workerID, i, hit=0;
workerID = *(int *)arg;
for (;;) {
sem_wait(&shared.full);
pthread_mutex_lock(&shared.mutex);
fd = shared.buf[shared.out];
printf("\n[C%d] Consumed. I got %d ...Valor do buffer: %d na posição %d\n\n\n", workerID, fd, shared.buf[shared.out], shared.out);
ftp(fd, hit);
shared.buf[shared.out] = 0;
shared.out = (shared.out+1)%BUFSIZE;
fflush(stdout);
printf("\n\n\n\nEstado do buffer:\n\n\n\n");
for (i = 0; i < BUFSIZE; i++) {
//printf("%d ", shared.buf[i]);
}
/* Release the buffer */
pthread_mutex_unlock(&shared.mutex);
/* Increment the number of full slots */
sem_post(&shared.empty);
hit++;
}
return NULL;
}
And this is the code for my producer thread:
item = socketfd;
sem_wait(&shared.empty);
pthread_mutex_lock(&shared.mutex);
shared.buf[shared.in] = item;
shared.in = (shared.in + 1) % BUFSIZE;
fflush(stdout);
pthread_mutex_unlock(&shared.mutex);
sem_post(&shared.full);
Everything is working properly but serving 22 files takes around 20 seconds whilst creating one thread per request takes around 2 seconds! This seems to be executing a thread at a time and I want to execute all of them "at the same time".
Am I doing something wrong in my implementation approach?

Answer 1

For those who might come here with a similar problem, here's the fix.
Thanks to #Martin James and #EOF.
void *Consumer(void *arg)
{
int fd, workerID, i, hit=0;
workerID = *(int *)arg;
for (;;) {
sem_wait(&shared.full);
pthread_mutex_lock(&shared.mutex);
fd = shared.buf[shared.out];
shared.buf[shared.out] = 0;
shared.out = (shared.out+1)%BUFSIZE;
pthread_mutex_unlock(&shared.mutex);
printf("\n[C%d] Consumed. I got %d ...Valor do buffer: %d na posição %d\n\n\n", workerID, fd, shared.buf[shared.out], shared.out);
ftp(fd, hit);
fflush(stdout);
printf("\n\n\n\nEstado do buffer:\n\n\n\n");
for (i = 0; i < BUFSIZE; i++) {
//printf("%d ", shared.buf[i]);
}
/* Release the buffer */
/* Increment the number of full slots */
sem_post(&shared.empty);
hit++;
}
return NULL;
}
The problem is that I was locking the mutex, executing a function and then unlocking the mutex. This is what was causing so much delay on the execution.