57 lines
2.8 KiB
Text
57 lines
2.8 KiB
Text
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CLASS::Clock
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categories::Scheduling>Clocks
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summary::abstract superclass for clocks
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related::Classes/AppClock, Classes/SystemClock, Classes/TempoClock
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DESCRIPTION::
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Clock is an abstract class: it only defines an abstract set of methods that
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all clocks should implement. See its subclasses: link::Classes/SystemClock::,
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link::Classes/TempoClock::, link::Classes/AppClock:: for specific
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implementations.
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subsection:: Scheduling
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A Clock keeps track of time and allows strong::tasks:: to be
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strong::scheduled:: for some time in the future (e.g. using
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link::Classes/TempoClock#-sched#sched::,
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link::Classes/TempoClock#-schedAbs#schedAbs:: or
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link::Classes/TempoClock#-play#play:: methods).
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A task can be any link::Classes/Object::. When the time at which a task was scheduled is up, the task is emphasis::awoken::, i.e. its
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link::Classes/Object#-awake#awake:: method is evaluated. If the value returned by
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this method is a number, the task is automatically strong::rescheduled:: for the
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time equal to its last scheduled time plus the return value (in
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link::Classes/TempoClock#-beats#beats::).
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subsection:: Useful Tasks
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Objects of different classes may do different things in response to being
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scheduled on a clock by having own implementation of the code::awake:: method.
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The link::Classes/Object#-awake:: method that all classes inherit simply
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calls the same object's link::Classes/Object#-next#next:: method, forwarding the
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code::beats:: argument as well as the return value, so subclasses may implement
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either one to equivalent effect, as far as clock scheduling is concerned.
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footnote:: However, note that the code::next:: method is also involved in the
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concept of link::Tutorials/Streams-Patterns-Events1.html#Streams#streams::.::
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Examples of useful objects to be scheduled on clocks:
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list::
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## link::Classes/Function#-awake:: method is implemented so as to call
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the function's own link::Classes/Function#-value:: method, effectively running
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the code within the function.
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## link::Classes/Routine#-awake:: calls own link::Classes/Routine#-next::, in
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turn starting or resuming the Routine's Function.
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## Some subclasses of link::Classes/Stream:: will have its code::next:: method
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do something useful aside from returning a new value in a stream.
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::
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subsection:: Scheduling and Threads
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Whenever a task is awaken, its code::awake:: method is called in the context of
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the link::Classes/Process#-mainThread#main thread::. Just before that, the main
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thread's link::Classes/Thread#-beats#logical time:: is set to the scheduling
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time of the awaken task, and its link::Classes/Thread#-clock#clock:: is set to
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the scheduling clock. Note however that if the task is a link::Classes/Routine::
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it will then immediately start or resume its Function, setting itself as the
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link::Classes/Thread#.thisThread#current thread::.
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