Method _getLoopOnThread

src/PyEventLoop.cc:141–211

static */

/* static */
PyEventLoop PyEventLoop::_getLoopOnThread(PyThreadState *tstate) {
  // Modified from Python 3.9 `get_running_loop` https://github.com/python/cpython/blob/7cb3a44/Modules/_asynciomodule.c#L241-L278

  PyObject *ts_dict;
  #if PY_VERSION_HEX >= 0x030d0000 // Python version is greater than 3.13
  // The private `_PyThreadState_GetDict(tstate)` API gets removed in Python 3.13.
  // However, simply replacing it with `PyThreadState_GetDict()` does not work,
  //   since the public `PyThreadState_GetDict()` API can only get from the current thread.
  // We need to somehow get the thread dictionary on the main thread instead of the current thread.
  //
  // UPDATE: We don't need the thread dictionary anymore.
  // To get the thread's running event-loop in Python 3.13 is as simple as `thread_state->asyncio_running_loop`
  {
    // Every `PyThreadState` is actually allocated with extra fields as a `_PyThreadStateImpl` struct
    // See https://github.com/python/cpython/blob/v3.13.0rc1/Include/internal/pycore_tstate.h#L17-L24
    using PyThreadStateHolder = struct { // _PyThreadStateImpl
      PyThreadState base;
      #if PY_VERSION_HEX >= 0x030e0000 // Python version is greater than 3.14
      // the struct is changed with more additional fields, see https://github.com/python/cpython/blob/v3.14.0rc3/Include/internal/pycore_tstate.h#L24-L40
      Py_ssize_t refcount;
      uintptr_t c_stack_top;
      uintptr_t c_stack_soft_limit;
      uintptr_t c_stack_hard_limit;
      #endif
      PyObject *asyncio_running_loop; // we only need the first few fields of `_PyThreadStateImpl`
    };

    // Modified from https://github.com/python/cpython/blob/v3.13.0rc1/Modules/_asynciomodule.c#L3205-L3210
    PyObject *loop = ((PyThreadStateHolder *)tstate)->asyncio_running_loop;
    if (loop == NULL) {
      return _loopNotFound();
    }

    Py_INCREF(loop);
    return PyEventLoop(loop);
  }
  #elif PY_VERSION_HEX >= 0x03090000 // Python version is greater than 3.9
  ts_dict = _PyThreadState_GetDict(tstate);  // borrowed reference
  #else // Python 3.8
  ts_dict = tstate->dict; // see https://github.com/python/cpython/blob/v3.8.17/Modules/_asynciomodule.c#L244-L245
  #endif
  if (ts_dict == NULL) {
    return _loopNotFound();
  }

  // TODO: Python `get_running_loop` caches the PyRunningLoopHolder, should we do it as well for the main thread?
  //    see https://github.com/python/cpython/blob/7cb3a44/Modules/_asynciomodule.c#L234-L239
  PyObject *rl = PyDict_GetItemString(ts_dict, "__asyncio_running_event_loop__");  // borrowed reference
  if (rl == NULL) {
    return _loopNotFound();
  }

#if PY_VERSION_HEX < 0x030c0000 // Python version is less than 3.12
  using PyRunningLoopHolder = struct {
    PyObject_HEAD
    PyObject *rl_loop;
  };