summaryrefslogtreecommitdiff
path: root/distbuild/mainloop.py
blob: f15a3ac12b8b8f4fbf033b5a815f192fa06ff4ee (plain)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
# 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, write to the Free Software Foundation, Inc.,
# 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA..


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