import threading
import inspect
import ctypes

__all__ = ['Thread2']


def _async_raise(tid, exctype):
  """raises the exception, performs cleanup if needed"""
  if not inspect.isclass(exctype):
    raise TypeError("Only types can be raised (not instances)")
  res = ctypes.pythonapi.PyThreadState_SetAsyncExc(
    tid, ctypes.py_object(exctype)
  )
  if res == 0:
    raise ValueError("invalid thread id")
  elif res != 1:
    # """if it returns a number greater than one, you're in trouble,
    # and you should call it again with exc=NULL to revert the effect"""
    ctypes.pythonapi.PyThreadState_SetAsyncExc(tid, 0)
    raise SystemError("PyThreadState_SetAsyncExc failed")


class Thread2(threading.Thread):
  def _get_my_tid(self):
    """determines this (self's) thread id"""
    if not self.isAlive():
      raise threading.ThreadError("the thread is not active")

    # do we have it cached?
    if hasattr(self, "_thread_id"):
      return self._thread_id

    # no, look for it in the _active dict
    for tid, tobj in threading._active.items():
      if tobj is self:
        self._thread_id = tid
        return tid

    raise AssertionError("could not determine the thread's id")

  def raise_exc(self, exctype):
    """raises the given exception type in the context of this thread"""
    _async_raise(self._get_my_tid(), exctype)

  def terminate(self):
    """raises SystemExit in the context of the given thread, which should 
        cause the thread to exit silently (unless caught)"""
    self.raise_exc(SystemExit)