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Copy pathAlignedMemoryAllocator.cpp
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88 lines (75 loc) · 3.8 KB
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/*
* Copyright (C) 2017-2023 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.
*/
#include "config.h"
#include "AlignedMemoryAllocator.h"
#include "BlockDirectory.h"
#include "Subspace.h"
namespace JSC {
AlignedMemoryAllocator::AlignedMemoryAllocator() = default;
AlignedMemoryAllocator::~AlignedMemoryAllocator() = default;
void AlignedMemoryAllocator::addDirectoryWithEmptyBlocks(BlockDirectory* directory)
{
ASSERT(directory->subspace()->alignedMemoryAllocator() == this);
// Sweeping announces every block it finishes with, so the already-listed case is the common one
// and skips the lock. Reading the flag unlocked is sound because directories join and leave this
// list on the mutator, or on a sweeper holding the API lock, never from two threads at once. A
// wrong read would cost reuse rather than correctness anyway: a directory left off the list is
// simply not stealable from until its next empty block or the next prepareForAllocation re-adds
// it. See the concurrency FIXME in LocalAllocator::tryAllocateWithoutCollecting before allocating
// from a second thread.
if (directory->m_isOnEmptyBlocksList.loadRelaxed())
return;
Locker locker { m_directoriesWithEmptyBlocksLock };
if (directory->m_isOnEmptyBlocksList.loadRelaxed())
return;
directory->m_isOnEmptyBlocksList.storeRelaxed(true);
directory->m_nextDirectoryWithEmptyBlocks = m_firstDirectoryWithEmptyBlocks;
m_firstDirectoryWithEmptyBlocks = directory;
}
BlockDirectory* AlignedMemoryAllocator::takeDirectoryWithEmptyBlocks()
{
Locker locker { m_directoriesWithEmptyBlocksLock };
BlockDirectory* directory = m_firstDirectoryWithEmptyBlocks;
if (!directory)
return nullptr;
m_firstDirectoryWithEmptyBlocks = directory->m_nextDirectoryWithEmptyBlocks;
directory->m_nextDirectoryWithEmptyBlocks = nullptr;
directory->m_isOnEmptyBlocksList.storeRelaxed(false);
return directory;
}
MarkedBlock::Handle* AlignedMemoryAllocator::findEmptyBlockToSteal()
{
// Popped before it is searched, not after: a directory that gains a block mid-search must be able
// to put itself back on, which it cannot do while the search still claims it. Directories
// announce themselves from under their own lock, so the list lock has to be dropped either way.
while (BlockDirectory* directory = takeDirectoryWithEmptyBlocks()) {
if (MarkedBlock::Handle* block = directory->findEmptyBlockToSteal()) {
addDirectoryWithEmptyBlocks(directory);
return block;
}
}
return nullptr;
}
} // namespace JSC