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# Copyright (c) 2018, Science and Technology Facilities Council
# This software is distributed under a BSD licence. See LICENSE.txt.
"""
future_mrcfile
--------------
Module which exports the :class:`FutureMrcFile` class.
Classes:
:class:`FutureMrcFile`: An object which represents an MRC file being
opened asynchronously.
"""
# Import Python 3 features for future-proofing
from __future__ import (absolute_import, division, print_function,
unicode_literals)
import threading
class FutureMrcFile(object):
"""Object representing an MRC file being opened asynchronously.
This API deliberately mimics a :class:`~concurrent.futures.Future` object
from the :mod:`concurrent.futures` module in Python 3.2+ (which we do
not use directly because this code still needs to run in Python 2.7).
"""
def __init__(self, open_function, args=(), kwargs={}):
"""Initialise a new :class:`FutureMrcFile` object.
This constructor starts a new thread which will invoke the callable
given in ``open_function`` with the given arguments.
Args:
open_function: The callable to use to open the MRC file. (This will
normally be :func:`mrcfile.open`, but could also be
:class:`~mrcfile.mrcfile.MrcFile` or any of its subclasses.)
args: A tuple of positional arguments to use when ``open_function``
is called. (Normally a 1-tuple containing the name of the file
to open.)
kwargs: A dictionary of keyword arguments to use when
``open_function`` is called.
"""
self._result_holder = [None]
self._open_function = open_function
self._thread = threading.Thread(target=self._run,
args=args,
kwargs=kwargs)
self._thread.start()
def _run(self, *args, **kwargs):
"""Call the open function and store the result in the holder list.
(For internal use only.)
"""
try:
mrc = self._open_function(*args, **kwargs)
self._result_holder[0] = mrc
except Exception as ex:
self._result_holder[0] = ex
def cancel(self):
"""Return :data:`False`.
(See :meth:`concurrent.futures.Future.cancel` for more details. This
implementation does not allow jobs to be cancelled.)
"""
return False
def cancelled(self):
"""Return :data:`False`.
(See :meth:`concurrent.futures.Future.cancelled` for more details.
This implementation does not allow jobs to be cancelled.)
"""
return False
def running(self):
"""Return :data:`True` if the :class:`~mrcfile.mrcfile.MrcFile` is
currently being opened.
(See :meth:`concurrent.futures.Future.running` for more details.)
"""
return self._thread.is_alive()
def done(self):
"""Return :data:`True` if the file opening has finished.
(See :meth:`concurrent.futures.Future.done` for more details.)
"""
return not self.running()
def result(self, timeout=None):
"""Return the :class:`~mrcfile.mrcfile.MrcFile` that has been opened.
(See :meth:`concurrent.futures.Future.result` for more details.)
Args:
timeout: Time to wait (in seconds) for the file opening to finish.
If ``timeout`` is not specified or is :data:`None`, there is no
limit to the wait time.
Returns:
An :class:`~mrcfile.mrcfile.MrcFile` object (or one of its
subclasses).
Raises:
:exc:`RuntimeError`: If the operation has not finished within the
time limit set by ``timeout``. (Note that the type of this
exception will change in future if this class is replaced by
:class:`concurrent.futures.Future`.)
:exc:`Exception`: Any exception raised by the
:class:`~mrcfile.mrcfile.MrcFile` opening operation will be
re-raised here.
"""
result = self._get_result(timeout)
if isinstance(result, Exception):
raise result
else:
return result
def exception(self, timeout=None):
"""Return the exception raised by the file opening operation.
(See :meth:`concurrent.futures.Future.exception` for more details.)
Args:
timeout: Time to wait (in seconds) for the operation to finish. If
``timeout`` is not specified or is :data:`None`, there is no
limit to the wait time.
Returns:
An :exc:`Exception`, if one was raised by the file opening
operation, or :data:`None` if no exception was raised.
Raises:
:exc:`RuntimeError`: If the operation has not finished within the
time limit set by ``timeout``. (Note that the type of this
exception will change in future if this class is replaced by
:class:`concurrent.futures.Future`.)
"""
result = self._get_result(timeout)
if isinstance(result, Exception):
return result
else:
return None
def _get_result(self, timeout):
"""Return the result or exception from the file opening operation.
(For internal use only.)
"""
self._thread.join(timeout=timeout)
if self._thread.is_alive():
raise RuntimeError('Timed out waiting for result')
return self._result_holder[0]
def add_done_callback(self, fn):
"""Not implemented.
(See :meth:`concurrent.futures.Future.add_done_callback` for more details.)
"""
raise NotImplementedError
|
