# coding: utf-8
"""
This module contains the implementation of :class:`~can.Notifier`.
"""
from typing import Iterable, List, Optional, Union
from can.bus import BusABC
from can.listener import Listener
from can.message import Message
import threading
import logging
import time
import asyncio
logger = logging.getLogger("can.Notifier")
[docs]class Notifier:
def __init__(
self,
bus: BusABC,
listeners: Iterable[Listener],
timeout: float = 1.0,
loop: Optional[asyncio.AbstractEventLoop] = None,
):
"""Manages the distribution of :class:`can.Message` instances to listeners.
Supports multiple buses and listeners.
.. Note::
Remember to call `stop()` after all messages are received as
many listeners carry out flush operations to persist data.
:param bus: A :ref:`bus` or a list of buses to listen to.
:param listeners: An iterable of :class:`~can.Listener`
:param timeout: An optional maximum number of seconds to wait for any message.
:param loop: An :mod:`asyncio` event loop to schedule listeners in.
"""
self.listeners = list(listeners)
self.bus = bus
self.timeout = timeout
self._loop = loop
#: Exception raised in thread
self.exception: Optional[Exception] = None
self._running = True
self._lock = threading.Lock()
self._readers: List[Union[int, threading.Thread]] = []
buses = self.bus if isinstance(self.bus, list) else [self.bus]
for bus in buses:
self.add_bus(bus)
[docs] def add_bus(self, bus: BusABC):
"""Add a bus for notification.
:param bus:
CAN bus instance.
"""
if (
self._loop is not None
and hasattr(bus, "fileno")
and bus.fileno() >= 0 # type: ignore
):
# Use file descriptor to watch for messages
reader = bus.fileno() # type: ignore
self._loop.add_reader(reader, self._on_message_available, bus)
else:
reader = threading.Thread(
target=self._rx_thread,
args=(bus,),
name='can.notifier for bus "{}"'.format(bus.channel_info),
)
reader.daemon = True
reader.start()
self._readers.append(reader)
[docs] def stop(self, timeout: float = 5):
"""Stop notifying Listeners when new :class:`~can.Message` objects arrive
and call :meth:`~can.Listener.stop` on each Listener.
:param timeout:
Max time in seconds to wait for receive threads to finish.
Should be longer than timeout given at instantiation.
"""
self._running = False
end_time = time.time() + timeout
for reader in self._readers:
if isinstance(reader, threading.Thread):
now = time.time()
if now < end_time:
reader.join(end_time - now)
elif self._loop:
# reader is a file descriptor
self._loop.remove_reader(reader)
for listener in self.listeners:
if hasattr(listener, "stop"):
listener.stop()
def _rx_thread(self, bus: BusABC):
msg = None
try:
while self._running:
if msg is not None:
with self._lock:
if self._loop is not None:
self._loop.call_soon_threadsafe(
self._on_message_received, msg
)
else:
self._on_message_received(msg)
msg = bus.recv(self.timeout)
except Exception as exc:
self.exception = exc
if self._loop is not None:
self._loop.call_soon_threadsafe(self._on_error, exc)
else:
self._on_error(exc)
raise
def _on_message_available(self, bus: BusABC):
msg = bus.recv(0)
if msg is not None:
self._on_message_received(msg)
def _on_message_received(self, msg: Message):
for callback in self.listeners:
res = callback(msg)
if self._loop is not None and asyncio.iscoroutine(res):
# Schedule coroutine
self._loop.create_task(res)
def _on_error(self, exc: Exception):
for listener in self.listeners:
if hasattr(listener, "on_error"):
listener.on_error(exc)
[docs] def add_listener(self, listener: Listener):
"""Add new Listener to the notification list.
If it is already present, it will be called two times
each time a message arrives.
:param listener: Listener to be added to the list to be notified
"""
self.listeners.append(listener)
[docs] def remove_listener(self, listener: Listener):
"""Remove a listener from the notification list. This method
trows an exception if the given listener is not part of the
stored listeners.
:param listener: Listener to be removed from the list to be notified
:raises ValueError: if `listener` was never added to this notifier
"""
self.listeners.remove(listener)