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/*
* Copyright (C) 2016-2023 Apple Inc. All rights reserved.
*
* Redistribution and use in source and binary forms, with or without
* modification, are permitted provided that the following conditions
* are met:
* 1. Redistributions of source code must retain the above copyright
* notice, this list of conditions and the following disclaimer.
* 2. Redistributions in binary form must reproduce the above copyright
* notice, this list of conditions and the following disclaimer in the
* documentation and/or other materials provided with the distribution.
*
* THIS SOFTWARE IS PROVIDED BY APPLE INC. ``AS IS'' AND ANY
* EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
* IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
* PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL APPLE INC. OR
* CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL,
* EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO,
* PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR
* PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY
* OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
* (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
* OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
*/
#pragma once
#include "MarkedBlock.h"
#include "WeakSet.h"
#include <wtf/StdLibExtras.h>
namespace JSC {
class IsoSubspace;
class SlotVisitor;
// WebKit has a good malloc that already knows what to do for large allocations. The GC shouldn't
// have to think about such things. That's where PreciseAllocation comes in. We will allocate large
// objects directly using malloc, and put the PreciseAllocation header just before them. We can detect
// when a HeapCell* is a PreciseAllocation because it will have the MarkedBlock::atomSize / 2 bit set.
class PreciseAllocation : public BasicRawSentinelNode<PreciseAllocation> {
public:
friend class LLIntOffsetsExtractor;
friend class IsoSubspace;
static PreciseAllocation* tryCreate(Heap&, size_t, Subspace*, unsigned indexInSpace);
static PreciseAllocation* tryCreateForLowerTier(Heap&, size_t, Subspace*, uint8_t lowerTierIndex);
PreciseAllocation* reuseForLowerTier();
PreciseAllocation* tryReallocate(size_t, Subspace*);
~PreciseAllocation();
static PreciseAllocation* fromCell(const void* cell)
{
return bitwise_cast<PreciseAllocation*>(bitwise_cast<char*>(cell) - headerSize());
}
HeapCell* cell() const
{
return bitwise_cast<HeapCell*>(bitwise_cast<char*>(this) + headerSize());
}
static bool isPreciseAllocation(HeapCell* cell)
{
return bitwise_cast<uintptr_t>(cell) & halfAlignment;
}
Subspace* subspace() const { return m_subspace; }
void lastChanceToFinalize();
JSC::Heap* heap() const { return m_weakSet.heap(); }
VM& vm() const { return m_weakSet.vm(); }
WeakSet& weakSet() { return m_weakSet; }
static ptrdiff_t offsetOfWeakSet() { return OBJECT_OFFSETOF(PreciseAllocation, m_weakSet); }
unsigned indexInSpace() { return m_indexInSpace; }
void setIndexInSpace(unsigned indexInSpace) { m_indexInSpace = indexInSpace; }
void clearNewlyAllocated() { m_isNewlyAllocated = false; }
void flip();
bool isNewlyAllocated() const { return m_isNewlyAllocated; }
ALWAYS_INLINE bool isMarked() { return m_isMarked.load(std::memory_order_relaxed); }
ALWAYS_INLINE bool isMarked(HeapCell*) { return isMarked(); }
ALWAYS_INLINE bool isMarked(HeapCell*, Dependency) { return isMarked(); }
ALWAYS_INLINE bool isMarked(HeapVersion, HeapCell*) { return isMarked(); }
bool isLive() { return isMarked() || isNewlyAllocated(); }
bool hasValidCell() const { return m_hasValidCell; }
bool isEmpty();
size_t cellSize() const { return m_cellSize; }
uint8_t lowerTierIndex() const { return m_lowerTierIndex; }
bool aboveLowerBound(const void* rawPtr)
{
char* ptr = bitwise_cast<char*>(rawPtr);
char* begin = bitwise_cast<char*>(cell());
return ptr >= begin;
}
bool belowUpperBound(const void* rawPtr)
{
char* ptr = bitwise_cast<char*>(rawPtr);
char* begin = bitwise_cast<char*>(cell());
char* end = begin + cellSize();
// We cannot #include IndexingHeader.h because reasons. The fact that IndexingHeader is 8
// bytes is wired deep into our engine, so this isn't so bad.
size_t sizeOfIndexingHeader = 8;
return ptr <= end + sizeOfIndexingHeader;
}
bool contains(const void* rawPtr)
{
return aboveLowerBound(rawPtr) && belowUpperBound(rawPtr);
}
CellAttributes attributes() const { return m_attributes; }
Dependency aboutToMark(HeapVersion) { return Dependency(); }
ALWAYS_INLINE bool testAndSetMarked()
{
// This method is usually called when the object is already marked. This avoids us
// having to CAS in that case. It's profitable to reduce the total amount of CAS
// traffic.
if (isMarked())
return true;
return m_isMarked.compareExchangeStrong(false, true);
}
ALWAYS_INLINE bool testAndSetMarked(HeapCell*, Dependency) { return testAndSetMarked(); }
void clearMarked() { m_isMarked.store(false); }
void noteMarked() { }
#if ASSERT_ENABLED
void assertValidCell(VM&, HeapCell*) const;
#else
void assertValidCell(VM&, HeapCell*) const { }
#endif
void sweep();
void destroy();
void dump(PrintStream&) const;
bool isLowerTier() const { return m_lowerTierIndex != UINT8_MAX; }
static constexpr unsigned alignment = MarkedBlock::atomSize;
static constexpr unsigned halfAlignment = alignment / 2;
static constexpr unsigned cacheLineAdjustment = 2 * halfAlignment;
// The header size must be packed to full alignment size. Because the cell start address
// always begins immediately after the header, this allows isAlignedForPreciseAllocation()
// to trivially infer the alignment of the cell from the alignment of the header.
static constexpr unsigned headerSize() { return roundUpToMultipleOf<alignment>(sizeof(PreciseAllocation)); }
private:
PreciseAllocation(Heap&, size_t, Subspace*, unsigned indexInSpace, unsigned adjustment);
void* basePointer() const;
unsigned m_indexInSpace { 0 };
size_t m_cellSize;
bool m_isNewlyAllocated : 1;
bool m_hasValidCell : 1;
// Worst case adjustment needed would be halfAlignment + portionOfObjectThatMustFitInCacheLine
// which is 8 + 16 -> 24 bytes i.e. will fit in 5 bits. If we need more bits in the future, we
// can also encode this number of uintptr_t words to save 3 bits.
unsigned m_adjustment : 5;
Atomic<bool> m_isMarked;
CellAttributes m_attributes;
uint8_t m_lowerTierIndex { UINT8_MAX };
Subspace* m_subspace;
WeakSet m_weakSet;
};
inline void* PreciseAllocation::basePointer() const
{
return bitwise_cast<char*>(this) - m_adjustment;
}
} // namespace JSC
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