Method PushFront

include/Eigen/Eigen/src/ThreadPool/RunQueue.h:55–66

PushFront inserts w at the beginning of the queue. If queue is full returns w, otherwise returns default-constructed Work.

  // PushFront inserts w at the beginning of the queue.
  // If queue is full returns w, otherwise returns default-constructed Work.
  Work PushFront(Work w) {
    unsigned front = front_.load(std::memory_order_relaxed);
    Elem* e = &array_[front & kMask];
    uint8_t s = e->state.load(std::memory_order_relaxed);
    if (s != kEmpty ||
        !e->state.compare_exchange_strong(s, kBusy, std::memory_order_acquire))
      return w;
    front_.store(front + 1 + (kSize << 1), std::memory_order_relaxed);
    e->w = std::move(w);
    e->state.store(kReady, std::memory_order_release);
    return Work();
  }

  // PopFront removes and returns the first element in the queue.
  // If the queue was empty returns default-constructed Work.