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zmq_loop.py
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zmq_loop.py
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# Urwid main loop code using ZeroMQ queues
# Copyright (C) 2019 Dave Jones
#
# This library is free software; you can redistribute it and/or
# modify it under the terms of the GNU Lesser General Public
# License as published by the Free Software Foundation; either
# version 2.1 of the License, or (at your option) any later version.
#
# This library is distributed in the hope that it will be useful,
# but WITHOUT ANY WARRANTY; without even the implied warranty of
# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
# Lesser General Public License for more details.
#
# You should have received a copy of the GNU Lesser General Public
# License along with this library; if not, write to the Free Software
# Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA
#
# Urwid web site: https://urwid.org/
"""ZeroMQ based urwid EventLoop implementation.
`ZeroMQ <https://zeromq.org>`_ library is required.
"""
from __future__ import annotations
import os
import time
import errno
import heapq
import typing
from itertools import count
from collections.abc import Callable
import zmq
from .abstract_loop import EventLoop, ExitMainLoop
ZMQAlarmHandle = typing.TypeVar('ZMQAlarmHandle')
ZMQQueueHandle = typing.TypeVar('ZMQQueueHandle')
ZMQFileHandle = typing.TypeVar('ZMQFileHandle')
ZMQIdleHandle = typing.TypeVar('ZMQIdleHandle')
class ZMQEventLoop(EventLoop):
"""
This class is an urwid event loop for `ZeroMQ`_ applications. It is very
similar to :class:`SelectEventLoop`, supporting the usual :meth:`alarm`
events and file watching (:meth:`watch_file`) capabilities, but also
incorporates the ability to watch zmq queues for events
(:meth:`watch_queue`).
.. _ZeroMQ: https://zeromq.org/
"""
_alarm_break = count()
def __init__(self):
self._did_something = True
self._alarms = []
self._poller = zmq.Poller()
self._queue_callbacks = {}
self._idle_handle = 0
self._idle_callbacks = {}
def alarm(self, seconds: float | int, callback: Callable[[], typing.Any]) -> ZMQAlarmHandle:
"""
Call *callback* a given time from now. No parameters are passed to
callback. Returns a handle that may be passed to :meth:`remove_alarm`.
:param float seconds:
floating point time to wait before calling callback.
:param callback:
function to call from event loop.
"""
handle = (time.time() + seconds, next(self._alarm_break), callback)
heapq.heappush(self._alarms, handle)
return handle
def remove_alarm(self, handle: ZMQAlarmHandle) -> bool:
"""
Remove an alarm. Returns ``True`` if the alarm exists, ``False``
otherwise.
"""
try:
self._alarms.remove(handle)
heapq.heapify(self._alarms)
return True
except ValueError:
return False
def watch_queue(self, queue: zmq.Socket, callback: Callable[[], typing.Any],
flags: int=zmq.POLLIN) -> ZMQQueueHandle:
"""
Call *callback* when zmq *queue* has something to read (when *flags* is
set to ``POLLIN``, the default) or is available to write (when *flags*
is set to ``POLLOUT``). No parameters are passed to the callback.
Returns a handle that may be passed to :meth:`remove_watch_queue`.
:param queue:
The zmq queue to poll.
:param callback:
The function to call when the poll is successful.
:param int flags:
The condition to monitor on the queue (defaults to ``POLLIN``).
"""
if queue in self._queue_callbacks:
raise ValueError('already watching %r' % queue)
self._poller.register(queue, flags)
self._queue_callbacks[queue] = callback
return queue
def watch_file(self, fd: int, callback: Callable[[], typing.Any],
flags: int=zmq.POLLIN) -> ZMQFileHandle:
"""
Call *callback* when *fd* has some data to read. No parameters are
passed to the callback. The *flags* are as for :meth:`watch_queue`.
Returns a handle that may be passed to :meth:`remove_watch_file`.
:param fd:
The file-like object, or fileno to monitor.
:param callback:
The function to call when the file has data available.
:param int flags:
The condition to monitor on the file (defaults to ``POLLIN``).
"""
if isinstance(fd, int):
fd = os.fdopen(fd)
self._poller.register(fd, flags)
self._queue_callbacks[fd.fileno()] = callback
return fd
def remove_watch_queue(self, handle: ZMQQueueHandle) -> bool:
"""
Remove a queue from background polling. Returns ``True`` if the queue
was being monitored, ``False`` otherwise.
"""
try:
try:
self._poller.unregister(handle)
finally:
self._queue_callbacks.pop(handle, None)
return True
except KeyError:
return False
def remove_watch_file(self, handle: ZMQFileHandle) -> bool:
"""
Remove a file from background polling. Returns ``True`` if the file was
being monitored, ``False`` otherwise.
"""
try:
try:
self._poller.unregister(handle)
finally:
self._queue_callbacks.pop(handle.fileno(), None)
return True
except KeyError:
return False
def enter_idle(self, callback: Callable[[], typing.Any]) -> ZMQIdleHandle:
"""
Add a *callback* to be executed when the event loop detects it is idle.
Returns a handle that may be passed to :meth:`remove_enter_idle`.
"""
self._idle_handle += 1
self._idle_callbacks[self._idle_handle] = callback
return self._idle_handle
def remove_enter_idle(self, handle: ZMQIdleHandle) -> bool:
"""
Remove an idle callback. Returns ``True`` if *handle* was removed,
``False`` otherwise.
"""
try:
del self._idle_callbacks[handle]
return True
except KeyError:
return False
def _entering_idle(self) -> None:
for callback in list(self._idle_callbacks.values()):
callback()
def run(self) -> None:
"""
Start the event loop. Exit the loop when any callback raises an
exception. If :exc:`ExitMainLoop` is raised, exit cleanly.
"""
try:
while True:
try:
self._loop()
except zmq.error.ZMQError as exc:
if exc.errno != errno.EINTR:
raise
except ExitMainLoop:
pass
def _loop(self) -> None:
"""
A single iteration of the event loop.
"""
if self._alarms or self._did_something:
if self._alarms:
state = 'alarm'
timeout = max(0, self._alarms[0][0] - time.time())
if self._did_something and (not self._alarms or
(self._alarms and timeout > 0)):
state = 'idle'
timeout = 0
ready = dict(self._poller.poll(timeout * 1000))
else:
state = 'wait'
ready = dict(self._poller.poll())
if not ready:
if state == 'idle':
self._entering_idle()
self._did_something = False
elif state == 'alarm':
due, tie_break, callback = heapq.heappop(self._alarms)
callback()
self._did_something = True
for queue, _ in ready.items():
self._queue_callbacks[queue]()
self._did_something = True