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98 lines
3.4 KiB
TeX
98 lines
3.4 KiB
TeX
\section{\module{sched} ---
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Event scheduler}
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% LaTeXed and enhanced from comments in file
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\declaremodule{standard}{sched}
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\sectionauthor{Moshe Zadka}{mzadka@geocities.com}
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\modulesynopsis{General purpose event scheduler.}
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The \module{sched} module defines a class which implements a general
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purpose event scheduler:\index{event scheduling}
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\begin{classdesc}{scheduler}{timefunc, delayfunc}
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The \class{scheduler} class defines a generic interface to scheduling
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events. It needs two functions to actually deal with the ``outside world''
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--- \var{timefunc} should be callable without arguments, and return
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a number (the ``time'', in any units whatsoever). The \var{delayfunc}
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function should be callable with one argument, compatible with the output
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of \var{timefunc}, and should delay that many time units.
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\var{delayfunc} will also be called with the argument \code{0} after
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each event is run to allow other threads an opportunity to run in
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multi-threaded applications.
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\end{classdesc}
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Example:
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\begin{verbatim}
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>>> import sched, time
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>>> s=sched.scheduler(time.time, time.sleep)
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>>> def print_time(): print "From print_time", time.time()
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...
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>>> def print_some_times():
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... print time.time()
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... s.enter(5, 1, print_time, ())
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... s.enter(10, 1, print_time, ())
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... s.run()
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... print time.time()
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...
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>>> print_some_times()
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930343690.257
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From print_time 930343695.274
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From print_time 930343700.273
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930343700.276
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\end{verbatim}
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\subsection{Scheduler Objects \label{scheduler-objects}}
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\class{scheduler} instances have the following methods:
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\begin{methoddesc}{enterabs}{time, priority, action, argument}
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Schedule a new event. The \var{time} argument should be a numeric type
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compatible with the return value of the \var{timefunc} function passed
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to the constructor. Events scheduled for
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the same \var{time} will be executed in the order of their
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\var{priority}.
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Executing the event means executing \code{apply(\var{action},
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\var{argument})}. \var{argument} must be a tuple holding the
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parameters for \var{action}.
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Return value is an event which may be used for later cancellation of
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the event (see \method{cancel()}).
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\end{methoddesc}
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\begin{methoddesc}{enter}{delay, priority, action, argument}
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Schedule an event for \var{delay} more time units. Other then the
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relative time, the other arguments, the effect and the return value
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are the same as those for \method{enterabs()}.
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\end{methoddesc}
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\begin{methoddesc}{cancel}{event}
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Remove the event from the queue. If \var{event} is not an event
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currently in the queue, this method will raise a
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\exception{RuntimeError}.
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\end{methoddesc}
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\begin{methoddesc}{empty}{}
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Return true if the event queue is empty.
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\end{methoddesc}
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\begin{methoddesc}{run}{}
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Run all scheduled events. This function will wait
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(using the \function{delayfunc} function passed to the constructor)
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for the next event, then execute it and so on until there are no more
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scheduled events.
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Either \var{action} or \var{delayfunc} can raise an exception. In
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either case, the scheduler will maintain a consistent state and
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propagate the exception. If an exception is raised by \var{action},
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the event will not be attempted in future calls to \method{run()}.
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If a sequence of events takes longer to run than the time available
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before the next event, the scheduler will simply fall behind. No
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events will be dropped; the calling code is responsible for cancelling
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events which are no longer pertinent.
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\end{methoddesc}
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