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typedef struct {
 char buf[BSIZE];   // if empty==BSIZE buffer is empty. if empty==0, then it's full
 sema_t occupied, empty;
 int nextin, nextout;
 sema_t pmutex, cmutex;
} BUFFER;

initialization section
BUFFER *bufferp; // allocate a pointer to a BUFFER
bufferp = malloc( sizeof(BUFFER) );                                // create a BUFFER type
sema_init(&buffer->occupied, 0, USYNC_THREAD, 0);     // force consumer to always wait first
sema_init(&buffer->empty, BSIZE, USYNC_THREAD, 0); // allow for BSIZE accesses, i.e, buf is empty
sema_init(&buffer->pmutex, 1, USYNC_THREAD, 0);       // producer mutex
sema_init(&buffer->cmutex, 1, USYNC_THREAD, 0);       // consumer mutex
bufferp->nextin = 0; // initialize ring buffer
cond_init( &count_nonzero, USYNC_THREAD, 0);          // intraprocesss usage

 
void producer (BUFFER *b, chare item) {
 sema_wait( &b->empty );
 sema_wait( &b->pmutex );                          // protect against other   producers accessing this buffer
 b->buf[ b->nextin ] = item;                           // insert datum
 b->nextin = (b->nextin + 1 ) % BSIZE;         // ring buffer
 sema_post( &b->pmutex );                         // allow other producers in
 sema_post( &b->occupied );                      // let any consumers know a  datum is available
}
 
char consumer(BUFFER *b) {
 char item;
 sema_wait( &b->occupied );                   // wait if another consumer or  producer is here
 sema_wait( &b->cmutex );                       // protect buffer against other  consumers
 item = b->buf[ b->nectout ];                     // get next datum from buffer
 b->nextout = (b->nextout + 1) BSIZE;       // ring buffer
 sema_post( &b->cmutex );                       // allow other consumers into  this buffer
 sema_post( &b->empty );                        // let producer know of buffer's  status
 return ( item );
}