weex_core/Source/include/JavaScriptCore/heap/CellState.h

/*
 * Copyright (C) 2015-2017 Apple Inc. All rights reserved.
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#pragma once

#include <wtf/Assertions.h>

namespace JSC {

// The CellState of a cell is a kind of hint about what the state of the cell is.
enum class CellState : uint8_t {
    // The object is either currently being scanned, or it has finished being scanned, or this
    // is a full collection and it's actually a white object (you'd know because its mark bit
    // would be clear).
    PossiblyBlack = 0,
    
    // The object is in eden. During GC, this means that the object has not been marked yet.
    DefinitelyWhite = 1,

    // This sorta means that the object is grey - i.e. it will be scanned. Or it could be white
    // during a full collection if its mark bit is clear. That would happen if it had been black,
    // got barriered, and we did a full collection.
    PossiblyGrey = 2
};

static const unsigned blackThreshold = 0; // x <= blackThreshold means x is PossiblyOldOrBlack.
static const unsigned tautologicalThreshold = 100; // x <= tautologicalThreshold is always true.

inline bool isWithinThreshold(CellState cellState, unsigned threshold)
{
    return static_cast<unsigned>(cellState) <= threshold;
}

} // namespace JSC