WebKit/Source/JavaScriptCore/tools/TieredMMapArray.h at main · WebKit/WebKit · GitHub

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* 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 <wtf/OSAllocator.h>

namespace JSC {

// This class implements a simple array class that can be grown by appending items to the end.

// This class is implemented purely in terms of system allocations, with no malloc/free, so that

// it can safely be used from a secondary thread whilst the main thrad is paused (potentially

// holding the fast malloc heap lock).

template<typename T>

class TieredMMapArray {

static const size_t entriesPerBlock = 4096;

public:

TieredMMapArray()

: m_directoryCount(4096)

, m_directory(static_cast<T**>(OSAllocator::reserveAndCommit(m_directoryCount * sizeof(T*))))

, m_size(0)

{

for (size_t block = 0; block < m_directoryCount; ++block)

m_directory[block] = 0;

}

~TieredMMapArray()

{

size_t usedCount = (m_size + (entriesPerBlock - 1)) / entriesPerBlock;

ASSERT(usedCount == m_directoryCount || !m_directory[usedCount]);

for (size_t block = 0; block < usedCount; ++block) {

ASSERT(m_directory[block]);

OSAllocator::decommitAndRelease(m_directory[block], entriesPerBlock * sizeof(T));

}

OSAllocator::decommitAndRelease(m_directory, m_directoryCount * sizeof(T*));

}

T& operator[](size_t index)

{

ASSERT(index < m_size);

size_t block = index / entriesPerBlock;

size_t offset = index % entriesPerBlock;

ASSERT(m_directory[block]);

return m_directory[block][offset];

}

void append(const T& value)

{

// Check if the array is completely full, if so create more capacity in the directory.

if (m_size == m_directoryCount * entriesPerBlock) {

// Reallocate the directory.

size_t oldDirectorySize = m_directoryCount * sizeof(T*);

size_t newDirectorySize = oldDirectorySize * 2;

RELEASE_ASSERT(newDirectorySize < oldDirectorySize);

m_directory = OSAllocator::reallocateCommitted(m_directory, oldDirectorySize, newDirectorySize);

size_t newDirectoryCount = m_directoryCount * 2;

for (size_t block = m_directoryCount; block < newDirectoryCount; ++block)

m_directory[block] = 0;

m_directoryCount = newDirectoryCount;

}

size_t index = m_size;

size_t block = index / entriesPerBlock;

size_t offset = index % entriesPerBlock;

if (!offset) {

ASSERT(!m_directory[block]);

m_directory[block] = static_cast<T*>(OSAllocator::reserveAndCommit(entriesPerBlock * sizeof(T)));

}

ASSERT(m_directory[block]);

++m_size;

m_directory[block][offset] = value;

}

size_t size() const { return m_size; }

private:

size_t m_directoryCount;

T** m_directory;

size_t m_size;

};

} // namespace JSC

WebKit/Source/JavaScriptCore/tools/TieredMMapArray.h at main · WebKit/WebKit · GitHub

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