Mesa style wait and signal algorithm

synch.cc

void Condition_H::Wait() {
    IntStatus oldLevel = interrupt->SetLevel(IntOff);

    count++;
    if (mon->next_count > 0) {
      mon->next->V();
      mon->next_count--;
    }
    else mon->mutex->V();
    sem->P();
    count--;

    (void) interrupt->SetLevel(oldLevel);
}

void Condition_H::Signal() {
    IntStatus oldLevel = interrupt->SetLevel(IntOff);
    if (count > 0)     {
      mon->next_count++;
      sem->V();

      mon->next->P();
      mon->next_count--;
    }
    (void) interrupt->SetLevel(oldLevel);
}