Class Lock

include/PyEventLoop.hh:264–306

  static PyEventLoop getMainLoop();

  struct Lock {
  public:
    explicit Lock() {
      PyObject *asyncio = PyImport_ImportModule("asyncio");
      _queueIsEmpty = PyObject_CallMethod(asyncio, "Event", NULL); // _queueIsEmpty = asyncio.Event()
      Py_DECREF(asyncio);

      // The flag should initially be set as the queue is initially empty
      Py_XDECREF(PyObject_CallMethod(_queueIsEmpty, "set", NULL)); // _queueIsEmpty.set()
    };
    ~Lock() {
      Py_DECREF(_queueIsEmpty);
    }

    /**
     * @brief Increment the counter for the number of our job functions in the Python event-loop
     */
    inline void incCounter() {
      _counter++;
      Py_XDECREF(PyObject_CallMethod(_queueIsEmpty, "clear", NULL)); // _queueIsEmpty.clear()
    }

    /**
     * @brief Decrement the counter for the number of our job functions in the Python event-loop
     */
    inline void decCounter() {
      _counter--;
      if (_counter == 0) { // no job queueing
        // Notify that the queue is empty and awake (unblock) the event-loop shield
        Py_XDECREF(PyObject_CallMethod(_queueIsEmpty, "set", NULL)); // _queueIsEmpty.set()
      } else if (_counter < 0) { // something went wrong
        PyErr_SetString(PyExc_RuntimeError, "Event-loop job counter went below zero.");
      }
    }

    /**
     * @brief An `asyncio.Event` instance to notify that there are no queued asynchronous jobs
     * @see https://docs.python.org/3/library/asyncio-sync.html#asyncio.Event
     */
    PyObject *_queueIsEmpty = nullptr;
  protected:
    std::atomic_int _counter = 0;
  };

  static inline PyEventLoop::Lock *_locker;