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61 lines
2.0 KiB
C++
61 lines
2.0 KiB
C++
//
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// Sleeper.h
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// Clock Signal
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//
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// Created by Thomas Harte on 20/08/2017.
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// Copyright © 2017 Thomas Harte. All rights reserved.
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//
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#ifndef Sleeper_hpp
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#define Sleeper_hpp
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/*!
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A sleeper is any component that sometimes requires a clock but at other times is 'asleep' — i.e. is not doing
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any clock-derived work, so needn't receive a clock. A disk controller is an archetypal example.
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A sleeper will signal sleeps and wakes to an observer.
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This is intended to allow for performance improvements to machines with components that can sleep. The observer
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callout is virtual so the intended use case is that a machine holds a component that might sleep. Its transitions
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into and out of sleep are sufficiently infrequent that a virtual call to announce them costs sufficiently little that
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the saved ::run_fors add up to a substantial amount.
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By convention, sleeper components must be willing to accept ::run_for even after announcing sleep. It's a hint,
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not a command.
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*/
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class Sleeper {
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public:
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Sleeper() : sleep_observer_(nullptr) {}
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class SleepObserver {
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public:
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/// Called to inform an observer that the component @c component has either gone to sleep or become awake.
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virtual void set_component_is_sleeping(void *component, bool is_sleeping) = 0;
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};
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/// Registers @c observer as the new sleep observer;
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void set_sleep_observer(SleepObserver *observer) {
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sleep_observer_ = observer;
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}
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/// @returns @c true if the component is currently sleeping; @c false otherwise.
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virtual bool is_sleeping() = 0;
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protected:
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/// Provided for subclasses; send sleep announcements to the sleep_observer_.
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SleepObserver *sleep_observer_;
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/*!
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Provided for subclasses; call this whenever is_sleeping might have changed, and the observer will be notified,
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if one exists.
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@c is_sleeping will be called only if there is an observer.
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*/
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void update_sleep_observer() {
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if(!sleep_observer_) return;
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sleep_observer_->set_component_is_sleeping(this, is_sleeping());
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}
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};
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#endif /* Sleeper_h */
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