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/*
* Copyright (C) 2010-2017 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. AND ITS CONTRIBUTORS ``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 ITS 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 "SharedStringHashStore.h"
#include <algorithm>
#include <wtf/PageBlock.h>
#include <wtf/StdLibExtras.h>
namespace WebKit {
using namespace WebCore;
const unsigned sharedStringHashTableMaxLoad = 2;
static unsigned nextPowerOf2(unsigned v)
{
// Taken from http://www.cs.utk.edu/~vose/c-stuff/bithacks.html
// Devised by Sean Anderson, September 14, 2001
v--;
v |= v >> 1;
v |= v >> 2;
v |= v >> 4;
v |= v >> 8;
v |= v >> 16;
v++;
return v;
}
static unsigned tableLengthForKeyCount(unsigned keyCount)
{
// We want the table to be at least half empty.
unsigned tableLength = nextPowerOf2(keyCount * sharedStringHashTableMaxLoad);
// Ensure that the table length is at least the size of a page.
size_t minimumTableLength = pageSize() / sizeof(SharedStringHash);
if (tableLength < minimumTableLength)
return minimumTableLength;
return tableLength;
}
SharedStringHashStore::SharedStringHashStore(Client& client)
: m_client(client)
, m_pendingOperationsTimer(RunLoop::main(), this, &SharedStringHashStore::processPendingOperations)
{
}
std::optional<SharedMemory::Handle> SharedStringHashStore::createSharedMemoryHandle()
{
return m_table.sharedMemory()->createHandle(SharedMemory::Protection::ReadOnly);
}
void SharedStringHashStore::scheduleAddition(SharedStringHash sharedStringHash)
{
m_pendingOperations.append({ Operation::Add, sharedStringHash });
if (!m_pendingOperationsTimer.isActive())
m_pendingOperationsTimer.startOneShot(0_s);
}
void SharedStringHashStore::scheduleRemoval(WebCore::SharedStringHash sharedStringHash)
{
m_pendingOperations.append({ Operation::Remove, sharedStringHash });
if (!m_pendingOperationsTimer.isActive())
m_pendingOperationsTimer.startOneShot(0_s);
}
bool SharedStringHashStore::contains(WebCore::SharedStringHash sharedStringHash)
{
flushPendingChanges();
return m_table.contains(sharedStringHash);
}
void SharedStringHashStore::clear()
{
m_pendingOperationsTimer.stop();
m_pendingOperations.clear();
m_keyCount = 0;
m_tableLength = 0;
m_table.clear();
}
void SharedStringHashStore::flushPendingChanges()
{
if (!m_pendingOperationsTimer.isActive())
return;
m_pendingOperationsTimer.stop();
processPendingOperations();
}
void SharedStringHashStore::resizeTable(unsigned newTableLength)
{
auto newTableMemory = SharedMemory::allocate((Checked<unsigned>(newTableLength) * sizeof(SharedStringHash)).value());
if (!newTableMemory) {
LOG_ERROR("Could not allocate shared memory for SharedStringHash table");
return;
}
zeroSpan(newTableMemory->mutableSpan());
RefPtr<SharedMemory> currentTableMemory = m_table.sharedMemory();
unsigned currentTableLength = m_tableLength;
m_table.setSharedMemory(newTableMemory.releaseNonNull());
m_tableLength = newTableLength;
if (currentTableMemory) {
RELEASE_ASSERT(currentTableMemory->size() == (Checked<unsigned>(currentTableLength) * sizeof(SharedStringHash)).value());
// Go through the current hash table and re-add all entries to the new hash table.
auto currentSharedStringHashes = spanReinterpretCast<const SharedStringHash>(currentTableMemory->span());
for (auto& sharedStringHash : currentSharedStringHashes) {
if (!sharedStringHash)
continue;
bool didAddSharedStringHash = m_table.add(sharedStringHash);
// It should always be possible to add the SharedStringHash to a new table.
ASSERT_UNUSED(didAddSharedStringHash, didAddSharedStringHash);
}
}
for (auto& operation : m_pendingOperations) {
switch (operation.type) {
case Operation::Add:
if (m_table.add(operation.sharedStringHash))
++m_keyCount;
break;
case Operation::Remove:
if (m_table.remove(operation.sharedStringHash))
--m_keyCount;
break;
}
}
m_pendingOperations.clear();
m_client.didInvalidateSharedMemory();
}
void SharedStringHashStore::processPendingOperations()
{
unsigned currentTableLength = m_tableLength;
unsigned approximateNewHashCount = std::count_if(m_pendingOperations.begin(), m_pendingOperations.end(), [](auto& operation) {
return operation.type == Operation::Add;
});
// FIXME: The table can currently only grow. We should probably support shrinking it to save memory.
unsigned newTableLength = tableLengthForKeyCount(m_keyCount + approximateNewHashCount);
newTableLength = std::max(currentTableLength, newTableLength);
if (currentTableLength != newTableLength) {
resizeTable(newTableLength);
return;
}
Vector<SharedStringHash> addedSharedStringHashes;
Vector<SharedStringHash> removedSharedStringHashes;
addedSharedStringHashes.reserveInitialCapacity(approximateNewHashCount);
removedSharedStringHashes.reserveInitialCapacity(m_pendingOperations.size() - approximateNewHashCount);
for (auto& operation : m_pendingOperations) {
switch (operation.type) {
case Operation::Add:
if (m_table.add(operation.sharedStringHash)) {
addedSharedStringHashes.append(operation.sharedStringHash);
++m_keyCount;
}
break;
case Operation::Remove:
if (m_table.remove(operation.sharedStringHash)) {
removedSharedStringHashes.append(operation.sharedStringHash);
--m_keyCount;
}
break;
}
}
m_pendingOperations.clear();
if (!addedSharedStringHashes.isEmpty() || !removedSharedStringHashes.isEmpty())
m_client.didUpdateSharedStringHashes(addedSharedStringHashes, removedSharedStringHashes);
}
} // namespace WebKit
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