Errata

bufGet() in buffer.c of example 14-4-5 only works for the first consumer.
Then it hangs because on consumer timeout the mutex is not unlocked.
Therefore cnd_timedwait cannot relock the mutex for the remaining consumers 2 and 3.

This works:

bool bufGet(Buffer *bufPtr, int *dataPtr, int sec) {
struct timespec ts;
timespec_get( &ts, TIME_UTC ); // The current time
ts.tv_sec += sec; // + sec seconds delay.
mtx_lock( &bufPtr->mtx );
while ( bufPtr->count == 0 ) {
int res = cnd_timedwait(&bufPtr->cndGet, &bufPtr->mtx, &ts);
if (res != thrd_success) {
mtx_unlock( &bufPtr->mtx ); // needed or other consumers will hang !
return false;
}
}
*dataPtr = bufPtr->data[bufPtr->tail];
bufPtr->tail = (bufPtr->tail + 1) % bufPtr->size;
--bufPtr->count;
mtx_unlock( &bufPtr->mtx );
cnd_signal( &bufPtr->cndPut );
thrd_yield();
return true;
}

Note from the Author or Editor:
The example works because a consumer thread is destroyed when bufGet() returns false.
But, of course, bufGet() should unlock the mutex. So replace the line

return false;

with

{ mtx_unlock( &bufPtr->mtx ); return false; }