1 """A generally useful event scheduler class.
2
3 Each instance of this class manages its own queue.
4 No multi-threading is implied; you are supposed to hack that
5 yourself, or use a single instance per application.
6
7 Each instance is parametrized with two functions, one that is
8 supposed to return the current time, one that is supposed to
9 implement a delay. You can implement real-time scheduling by
10 substituting time and sleep from built-in module time, or you can
11 implement simulated time by writing your own functions. This can
12 also be used to integrate scheduling with STDWIN events; the delay
13 function is allowed to modify the queue. Time can be expressed as
14 integers or floating point numbers, as long as it is consistent.
15
16 Events are specified by tuples (time, priority, action, argument, kwargs).
17 As in UNIX, lower priority numbers mean higher priority; in this
18 way the queue can be maintained as a priority queue. Execution of the
19 event means calling the action function, passing it the argument
20 sequence in "argument" (remember that in Python, multiple function
21 arguments are be packed in a sequence) and keyword parameters in "kwargs".
22 The action function may be an instance method so it
23 has another way to reference private data (besides global variables).
24 """
25
26 import time
27 import heapq
28 from collections import namedtuple
29 from itertools import count
30 import threading
31 from time import monotonic as _time
32
33 __all__ = ["scheduler"]
34
35 Event = namedtuple('Event', 'time, priority, sequence, action, argument, kwargs')
36 Event.time.__doc__ = ('''Numeric type compatible with the return value of the
37 timefunc function passed to the constructor.''')
38 Event.priority.__doc__ = ('''Events scheduled for the same time will be executed
39 in the order of their priority.''')
40 Event.sequence.__doc__ = ('''A continually increasing sequence number that
41 separates events if time and priority are equal.''')
42 Event.action.__doc__ = ('''Executing the event means executing
43 action(*argument, **kwargs)''')
44 Event.argument.__doc__ = ('''argument is a sequence holding the positional
45 arguments for the action.''')
46 Event.kwargs.__doc__ = ('''kwargs is a dictionary holding the keyword
47 arguments for the action.''')
48
49 _sentinel = object()
50
51 class ESC[4;38;5;81mscheduler:
52
53 def __init__(self, timefunc=_time, delayfunc=time.sleep):
54 """Initialize a new instance, passing the time and delay
55 functions"""
56 self._queue = []
57 self._lock = threading.RLock()
58 self.timefunc = timefunc
59 self.delayfunc = delayfunc
60 self._sequence_generator = count()
61
62 def enterabs(self, time, priority, action, argument=(), kwargs=_sentinel):
63 """Enter a new event in the queue at an absolute time.
64
65 Returns an ID for the event which can be used to remove it,
66 if necessary.
67
68 """
69 if kwargs is _sentinel:
70 kwargs = {}
71
72 with self._lock:
73 event = Event(time, priority, next(self._sequence_generator),
74 action, argument, kwargs)
75 heapq.heappush(self._queue, event)
76 return event # The ID
77
78 def enter(self, delay, priority, action, argument=(), kwargs=_sentinel):
79 """A variant that specifies the time as a relative time.
80
81 This is actually the more commonly used interface.
82
83 """
84 time = self.timefunc() + delay
85 return self.enterabs(time, priority, action, argument, kwargs)
86
87 def cancel(self, event):
88 """Remove an event from the queue.
89
90 This must be presented the ID as returned by enter().
91 If the event is not in the queue, this raises ValueError.
92
93 """
94 with self._lock:
95 self._queue.remove(event)
96 heapq.heapify(self._queue)
97
98 def empty(self):
99 """Check whether the queue is empty."""
100 with self._lock:
101 return not self._queue
102
103 def run(self, blocking=True):
104 """Execute events until the queue is empty.
105 If blocking is False executes the scheduled events due to
106 expire soonest (if any) and then return the deadline of the
107 next scheduled call in the scheduler.
108
109 When there is a positive delay until the first event, the
110 delay function is called and the event is left in the queue;
111 otherwise, the event is removed from the queue and executed
112 (its action function is called, passing it the argument). If
113 the delay function returns prematurely, it is simply
114 restarted.
115
116 It is legal for both the delay function and the action
117 function to modify the queue or to raise an exception;
118 exceptions are not caught but the scheduler's state remains
119 well-defined so run() may be called again.
120
121 A questionable hack is added to allow other threads to run:
122 just after an event is executed, a delay of 0 is executed, to
123 avoid monopolizing the CPU when other threads are also
124 runnable.
125
126 """
127 # localize variable access to minimize overhead
128 # and to improve thread safety
129 lock = self._lock
130 q = self._queue
131 delayfunc = self.delayfunc
132 timefunc = self.timefunc
133 pop = heapq.heappop
134 while True:
135 with lock:
136 if not q:
137 break
138 (time, priority, sequence, action,
139 argument, kwargs) = q[0]
140 now = timefunc()
141 if time > now:
142 delay = True
143 else:
144 delay = False
145 pop(q)
146 if delay:
147 if not blocking:
148 return time - now
149 delayfunc(time - now)
150 else:
151 action(*argument, **kwargs)
152 delayfunc(0) # Let other threads run
153
154 @property
155 def queue(self):
156 """An ordered list of upcoming events.
157
158 Events are named tuples with fields for:
159 time, priority, action, arguments, kwargs
160
161 """
162 # Use heapq to sort the queue rather than using 'sorted(self._queue)'.
163 # With heapq, two events scheduled at the same time will show in
164 # the actual order they would be retrieved.
165 with self._lock:
166 events = self._queue[:]
167 return list(map(heapq.heappop, [events]*len(events)))