Source/JavaScriptCore/heap/SpaceTimeScheduler.h

/*
 * Copyright (C) 2016 Apple Inc. All rights reserved.
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 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
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 *
 * THIS SOFTWARE IS PROVIDED BY APPLE INC. ``AS IS'' AND ANY
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 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
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#pragma once

#include <wtf/MonotonicTime.h>
#include <wtf/Seconds.h>

namespace JSC {

class Heap;

class SpaceTimeScheduler {
public:
    class Decision {
    public:
        explicit operator bool() const { return !!m_scheduler; }
        
        double targetMutatorUtilization() const;
        double targetCollectorUtilization() const;
        Seconds elapsedInPeriod() const;
        double phase() const;
        bool shouldBeResumed() const;
        MonotonicTime timeToResume() const;
        MonotonicTime timeToStop() const;
        
    private:
        friend class SpaceTimeScheduler;

        SpaceTimeScheduler* m_scheduler { nullptr };
        double m_bytesAllocatedThisCycle { 0 };
        MonotonicTime m_now;
    };
    
    // Construct the scheduler at the start of a GC cycle.
    SpaceTimeScheduler(Heap&);
    
    // Forces the next phase to start now.
    void snapPhase();
    
    // Returns a snapshot of the current scheduling decision, which will be valid so long as
    // SpaceTimeScheduler is live and you haven't called snapPhase().
    Decision currentDecision();
    
private:
    friend class Decision;

    Heap& m_heap;
    Seconds m_period;
    double m_bytesAllocatedThisCycleAtTheBeginning;
    double m_bytesAllocatedThisCycleAtTheEnd;
    MonotonicTime m_initialTime;
};

} // namespace JSC