Unix™ Systems Programming [Electronic resources] : Communication, Concurrency, and Threads

16.5 Bounded Buffer Implementation Using Condition Variables

Program 16.6.

Program 16.10 buffercond.c

Condition variable implementation of a bounded buffer.

#include <pthread.h>
#include "buffer.h"
static buffer_t buffer[BUFSIZE];
static pthread_mutex_t bufferlock = PTHREAD_MUTEX_INITIALIZER;
static int bufin = 0;
static int bufout = 0;
static pthread_cond_t items = PTHREAD_COND_INITIALIZER;
static pthread_cond_t slots = PTHREAD_COND_INITIALIZER;
static int totalitems = 0;
int getitem(buffer_t *itemp) { /* remove an item from buffer and put in itemp */
int error;
if (error = pthread_mutex_lock(&bufferlock))
return error;
while ((totalitems <= 0) && !error)
error = pthread_cond_wait (&items, &bufferlock);
if (error) {
pthread_mutex_unlock(&bufferlock);
return error;
}
*itemp = buffer[bufout];
bufout = (bufout + 1) % BUFSIZE;
totalitems--;
if (error = pthread_cond_signal(&slots)) {
pthread_mutex_unlock(&bufferlock);
return error;
}
return pthread_mutex_unlock(&bufferlock);
}
int putitem(buffer_t item) {                  /* insert an item in the buffer */
int error;
if (error = pthread_mutex_lock(&bufferlock))
return error;
while ((totalitems >= BUFSIZE) && !error)
error = pthread_cond_wait (&slots, &bufferlock);
if (error) {
pthread_mutex_unlock(&bufferlock);
return error;
}
buffer[bufin] = item;
bufin = (bufin + 1) % BUFSIZE;
totalitems++;
if (error = pthread_cond_signal(&items)) {
pthread_mutex_unlock(&bufferlock);
return error;
}
return pthread_mutex_unlock(&bufferlock);
}

Programs 16.7, 16.8 and 16.9. It also needs Program 13.4 (globalerror), Program 13.2 (randsafe) and Program 13.5 (sharedsum).