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# coding: utf-8
from __future__ import print_function, absolute_import
from threading import RLock
try:
# Only raise an exception on instantiation but allow module
# to be imported
from wrapt import ObjectProxy
import_exc = None
except ImportError as exc:
ObjectProxy = object
import_exc = exc
from .interface import Bus
try:
from contextlib import nullcontext
except ImportError:
class nullcontext(object):
"""A context manager that does nothing at all.
A fallback for Python 3.7's :class:`contextlib.nullcontext` manager.
"""
def __init__(self, enter_result=None):
self.enter_result = enter_result
def __enter__(self):
return self.enter_result
def __exit__(self, *args):
pass
class ThreadSafeBus(ObjectProxy):
"""
Contains a thread safe :class:`can.BusABC` implementation that
wraps around an existing interface instance. All public methods
of that base class are now safe to be called from multiple threads.
The send and receive methods are synchronized separately.
Use this as a drop-in replacement for :class:`~can.BusABC`.
.. note::
This approach assumes that both :meth:`~can.BusABC.send` and
:meth:`~can.BusABC._recv_internal` of the underlying bus instance can be
called simultaneously, and that the methods use :meth:`~can.BusABC._recv_internal`
instead of :meth:`~can.BusABC.recv` directly.
"""
def __init__(self, *args, **kwargs):
if import_exc is not None:
raise import_exc
super(ThreadSafeBus, self).__init__(Bus(*args, **kwargs))
# now, BusABC.send_periodic() does not need a lock anymore, but the
# implementation still requires a context manager
self.__wrapped__._lock_send_periodic = nullcontext()
# init locks for sending and receiving separately
self._lock_send = RLock()
self._lock_recv = RLock()
def recv(self, timeout=None, *args, **kwargs):
with self._lock_recv:
return self.__wrapped__.recv(timeout=timeout, *args, **kwargs)
def send(self, msg, timeout=None, *args, **kwargs):
with self._lock_send:
return self.__wrapped__.send(msg, timeout=timeout, *args, **kwargs)
# send_periodic does not need a lock, since the underlying
# `send` method is already synchronized
@property
def filters(self):
with self._lock_recv:
return self.__wrapped__.filters
@filters.setter
def filters(self, filters):
with self._lock_recv:
self.__wrapped__.filters = filters
def set_filters(self, can_filters=None, *args, **kwargs):
with self._lock_recv:
return self.__wrapped__.set_filters(can_filters=can_filters, *args, **kwargs)
def flush_tx_buffer(self, *args, **kwargs):
with self._lock_send:
return self.__wrapped__.flush_tx_buffer(*args, **kwargs)
def shutdown(self, *args, **kwargs):
with self._lock_send, self._lock_recv:
return self.__wrapped__.shutdown(*args, **kwargs)
@property
def state(self):
with self._lock_send, self._lock_recv:
return self.__wrapped__.state
@state.setter
def state(self, new_state):
with self._lock_send, self._lock_recv:
self.__wrapped__.state = new_state
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