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# mainloop/mainloop.py -- select-based main loop
#
# Copyright (C) 2012, 2014-2015 Codethink Limited
#
# This program is free software; you can redistribute it and/or modify
# it under the terms of the GNU General Public License as published by
# the Free Software Foundation; version 2 of the License.
#
# This program 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 General Public License for more details.
#
# You should have received a copy of the GNU General Public License along
# with this program. If not, see <http://www.gnu.org/licenses/>.
import fcntl
import logging
import os
import select
class MainLoop(object):
'''A select-based main loop.
The main loop watches a set of file descriptors wrapped in
EventSource objects, and when something happens with them,
asks the EventSource objects to create events, which it then
feeds into user-supplied state machines. The state machines
can create further events, which are processed further.
When nothing is happening, the main loop sleeps in the
select.select call.
'''
def __init__(self):
self._machines = []
self._sources = []
self._events = []
self.dump_filename = None
def add_state_machine(self, machine):
logging.debug('MainLoop.add_state_machine: %s' % machine)
machine.mainloop = self
machine.setup()
self._machines.append(machine)
if self.dump_filename:
filename = '%s%s.dot' % (self.dump_filename,
machine.__class__.__name__)
machine.dump_dot(filename)
def remove_state_machine(self, machine):
logging.debug('MainLoop.remove_state_machine: %s' % machine)
self._machines.remove(machine)
def state_machines_of_type(self, machine_type):
return [m for m in self._machines if isinstance(m, machine_type)]
def n_state_machines_of_type(self, machine_type):
return len(self.state_machines_of_type(machine_type))
def add_event_source(self, event_source):
logging.debug('MainLoop.add_event_source: %s' % event_source)
self._sources.append(event_source)
def remove_event_source(self, event_source):
logging.debug('MainLoop.remove_event_source: %s' % event_source)
self._sources.remove(event_source)
def _setup_select(self):
r = []
w = []
x = []
timeout = None
self._sources = [s for s in self._sources if not s.is_finished()]
for event_source in self._sources:
sr, sw, sx, st = event_source.get_select_params()
r.extend(sr)
w.extend(sw)
x.extend(sx)
if timeout is None:
timeout = st
elif st is not None:
timeout = min(timeout, st)
return r, w, x, timeout
def _run_once(self):
r, w, x, timeout = self._setup_select()
assert r or w or x or timeout is not None
r, w, x = select.select(r, w, x, timeout)
for event_source in self._sources:
if event_source.is_finished():
self.remove_event_source(event_source)
else:
for event in event_source.get_events(r, w, x):
self.queue_event(event_source, event)
for event_source, event in self._dequeue_events():
for machine in self._machines[:]:
for new_event in machine.handle_event(event_source, event):
self.queue_event(event_source, new_event)
if machine.state is None:
self.remove_state_machine(machine)
def run(self):
'''Run the main loop.
The main loop terminates when there are no state machines to
run anymore.
'''
logging.debug('MainLoop starts')
while self._machines:
self._run_once()
logging.debug('MainLoop ends')
def queue_event(self, event_source, event):
'''Add an event to queue of events to be processed.'''
self._events.append((event_source, event))
def _dequeue_events(self):
while self._events:
event_source, event = self._events.pop(0)
yield event_source, event
class TestableMainLoop(MainLoop):
'''Special mainloop class with extra hooks for tests to use.
When writing a test, you often need to wait until a certain event has
happened, then examine that event. The run_until_event() and
run_until_new_state_machine() functions allow this.
'''
def __init__(self):
super(TestableMainLoop, self).__init__()
self._machines_added_this_cycle = []
self._events_sent_this_cycle = []
def add_state_machine(self, machine):
# Overriding the base class to monitor new state machines.
super(TestableMainLoop, self).add_state_machine(machine)
self._machines_added_this_cycle.append(machine)
def queue_event(self, event_source, event):
# Overriding the base class to monitor new events.
super(TestableMainLoop, self).queue_event(event_source, event)
self._events_sent_this_cycle.append((event_source, event))
def run_until_event(self, target_event_source, target_event_type):
'''Run the main loop continuously until a given event happens.
All queued messages will be processed before the loop exits.
'''
logging.debug('Running main loop until a %s event from %s.',
target_event_type, target_event_source)
while self._machines:
self._events_sent_this_cycle = []
self._run_once()
for event_source, event in self._events_sent_this_cycle:
if target_event_source == event_source:
if isinstance(event, target_event_type):
logging.debug(
'Received %s from %s, exiting loop.', event,
event_source)
return event
def run_until_new_state_machine(self, target_machine_type):
'''Run the main loop continuously until a new state machine appears.
All queued messages will be processed before the loop exits.
'''
logging.debug('Running main loop until a new %s appears.',
target_machine_type)
while self._machines:
self._machines_added_this_cycle = []
self._run_once()
for machine in self._machines_added_this_cycle:
if type(machine) == target_machine_type:
logging.debug(
'Found new machine %s, exiting loop.', machine)
return machine
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