C - circular character buffer w/ pthreads

I have a homework assignment where I have to implement a circular buffer and add and remove chars with separate threads:

#include <pthread.h>
#include <stdio.h>

#define QSIZE 10

pthread_cond_t full,/* count == QSIZE */ 
           empty,/* count == 0 */ 
           ready;
pthread_mutex_t m, n; /* implements critical section */ 
unsigned int iBuf, /* tail of circular queue */ 
         oBuf; /* head of circular queue */ 
int count; /* count characters */ 
char buf [QSIZE]; /* the circular queue */ 

void Put(char s[]) {/* add "ch"; wait if full */
    pthread_mutex_lock(&m); 
    int size = sizeof(s)/sizeof(char);
    printf("size: %d", size);

    int i;
    for(i = 0; i < size;开发者_开发问答 i++) {
        while (count >= QSIZE) 
            pthread_cond_wait(&full, &m);/* is there empty slot? */ 

        buf[iBuf] = s[i]; /* store the character */ 
        iBuf = (iBuf+1) % QSIZE; /* increment mod QSIZE */ 
        count++; 
        if (count == 1) 
            pthread_cond_signal(&empty);/* new character available */ 
    }
    pthread_mutex_unlock(&m); 
} 
char Get() {/* remove "ch" from queue; wait if empty */ 
    char ch; 

    pthread_mutex_lock(&m); 
    while (count <= 0) 
        pthread_cond_wait(&empty, &m);/* is a character present? */ 

    ch = buf[oBuf]; /* retrieve from the head of the queue */ 
    oBuf = (oBuf+1) % QSIZE; 
    count--; 
    if (count == QSIZE-1) 
        pthread_cond_signal(&full);/* signal existence of a slot */ 

    pthread_mutex_unlock(&m); 
    return ch; 
} 

void * p1(void *arg) {
    int i;
    for (i = 0; i < 5; i++) {
        Put("hella");
    }
}

void * p2(void *arg) {
    int i;
    for (i = 0; i < 5; i++) {
        Put("goodby");
    }
}

int main() { 
    pthread_t t1, t2;
    void *r1, *r2;
    oBuf = 0; iBuf = 0; count=0; /* all slots are empty */ 

    pthread_cond_init(&full, NULL); 
    pthread_cond_init(&empty, NULL); 
    pthread_mutex_init(&m, NULL); 

    pthread_create(&t1, NULL, p1, &r1);
    pthread_create(&t2, NULL, p2, &r2);

    printf("Main");
    char c;
    int i = 0;
    while (i < 55) {
        c = Get();
        printf("%c",c);
        i++;
    }

    pthread_join(t1, &r1);
    pthread_join(t2, &r2);
    return 0; 
}

I shouldn't have to change the logic much at all, the requirements are pretty specific. I think my problem lies in the Put() method. I think the first thread is going in and blocking the critical section and causing a deadlock. I was thinking I should make a scheduling attribute? Of course I could be wrong. I am pretty new to pthreads and concurrent programming, so I could really use some help spotting my error.

---

One way to solve this would be to have separate mutexes to manage the head and tail of the circular queue. This way, a writer blocking because the buffer is full will not block a reader.

Another solution would be to release the mutex if you run into the buffer full or empty conditions and reacquire when the condition clears.

-lou