Method _register

Lib/asyncio/windows_events.py:715–745

(self, ov, obj, callback)

            # that succeed immediately.

    def _register(self, ov, obj, callback):
        self._check_closed()

        # Return a future which will be set with the result of the
        # operation when it completes.  The future's value is actually
        # the value returned by callback().
        f = _OverlappedFuture(ov, loop=self._loop)
        if f._source_traceback:
            del f._source_traceback[-1]
        if not ov.pending:
            # The operation has completed, so no need to postpone the
            # work.  We cannot take this short cut if we need the
            # NumberOfBytes, CompletionKey values returned by
            # PostQueuedCompletionStatus().
            try:
                value = callback(None, None, ov)
            except OSError as e:
                f.set_exception(e)
            else:
                f.set_result(value)
            # Even if GetOverlappedResult() was called, we have to wait for the
            # notification of the completion in GetQueuedCompletionStatus().
            # Register the overlapped operation to keep a reference to the
            # OVERLAPPED object, otherwise the memory is freed and Windows may
            # read uninitialized memory.

        # Register the overlapped operation for later.  Note that
        # we only store obj to prevent it from being garbage
        # collected too early.
        self._cache[ov.address] = (f, ov, obj, callback)
        return f

    def _unregister(self, ov):
        """Unregister an overlapped object.