107 lines
4.1 KiB
Python
107 lines
4.1 KiB
Python
"""A generally useful event scheduler class.
|
|
|
|
Each instance of this class manages its own queue.
|
|
No multi-threading is implied; you are supposed to hack that
|
|
yourself, or use a single instance per application.
|
|
|
|
Each instance is parametrized with two functions, one that is
|
|
supposed to return the current time, one that is supposed to
|
|
implement a delay. You can implement real-time scheduling by
|
|
substituting time and sleep from built-in module time, or you can
|
|
implement simulated time by writing your own functions. This can
|
|
also be used to integrate scheduling with STDWIN events; the delay
|
|
function is allowed to modify the queue. Time can be expressed as
|
|
integers or floating point numbers, as long as it is consistent.
|
|
|
|
Events are specified by tuples (time, priority, action, argument).
|
|
As in UNIX, lower priority numbers mean higher priority; in this
|
|
way the queue can be maintained fully sorted. Execution of the
|
|
event means calling the action function, passing it the argument.
|
|
Remember that in Python, multiple function arguments can be packed
|
|
in a tuple. The action function may be an instance method so it
|
|
has another way to reference private data (besides global variables).
|
|
Parameterless functions or methods cannot be used, however.
|
|
"""
|
|
|
|
# XXX The timefunc and delayfunc should have been defined as methods
|
|
# XXX so you can define new kinds of schedulers using subclassing
|
|
# XXX instead of having to define a module or class just to hold
|
|
# XXX the global state of your particular time and delay functions.
|
|
|
|
import bisect
|
|
|
|
__all__ = ["scheduler"]
|
|
|
|
class scheduler:
|
|
def __init__(self, timefunc, delayfunc):
|
|
"""Initialize a new instance, passing the time and delay
|
|
functions"""
|
|
self.queue = []
|
|
self.timefunc = timefunc
|
|
self.delayfunc = delayfunc
|
|
|
|
def enterabs(self, time, priority, action, argument):
|
|
"""Enter a new event in the queue at an absolute time.
|
|
|
|
Returns an ID for the event which can be used to remove it,
|
|
if necessary.
|
|
|
|
"""
|
|
event = time, priority, action, argument
|
|
bisect.insort(self.queue, event)
|
|
return event # The ID
|
|
|
|
def enter(self, delay, priority, action, argument):
|
|
"""A variant that specifies the time as a relative time.
|
|
|
|
This is actually the more commonly used interface.
|
|
|
|
"""
|
|
time = self.timefunc() + delay
|
|
return self.enterabs(time, priority, action, argument)
|
|
|
|
def cancel(self, event):
|
|
"""Remove an event from the queue.
|
|
|
|
This must be presented the ID as returned by enter().
|
|
If the event is not in the queue, this raises RuntimeError.
|
|
|
|
"""
|
|
self.queue.remove(event)
|
|
|
|
def empty(self):
|
|
"""Check whether the queue is empty."""
|
|
return len(self.queue) == 0
|
|
|
|
def run(self):
|
|
"""Execute events until the queue is empty.
|
|
|
|
When there is a positive delay until the first event, the
|
|
delay function is called and the event is left in the queue;
|
|
otherwise, the event is removed from the queue and executed
|
|
(its action function is called, passing it the argument). If
|
|
the delay function returns prematurely, it is simply
|
|
restarted.
|
|
|
|
It is legal for both the delay function and the action
|
|
function to to modify the queue or to raise an exception;
|
|
exceptions are not caught but the scheduler's state remains
|
|
well-defined so run() may be called again.
|
|
|
|
A questionably hack is added to allow other threads to run:
|
|
just after an event is executed, a delay of 0 is executed, to
|
|
avoid monopolizing the CPU when other threads are also
|
|
runnable.
|
|
|
|
"""
|
|
q = self.queue
|
|
while q:
|
|
time, priority, action, argument = q[0]
|
|
now = self.timefunc()
|
|
if now < time:
|
|
self.delayfunc(time - now)
|
|
else:
|
|
del q[0]
|
|
void = action(*argument)
|
|
self.delayfunc(0) # Let other threads run
|