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/**
* Copyright Amazon.com, Inc. or its affiliates. All Rights Reserved.
* SPDX-License-Identifier: Apache-2.0.
*/
#include <aws/core/utils/threading/ReaderWriterLock.h>
#include <cstdint>
#include <limits>
#include <cassert>
using namespace Aws::Utils::Threading;
static const int64_t MaxReaders = (std::numeric_limits<std::int32_t>::max)();
ReaderWriterLock::ReaderWriterLock() :
m_readers(0),
m_holdouts(0),
m_readerSem(0, static_cast<size_t>(MaxReaders)),
m_writerSem(0, 1)
{
}
void ReaderWriterLock::LockReader()
{
if (++m_readers < 0)
{
m_readerSem.WaitOne();
}
}
void ReaderWriterLock::UnlockReader()
{
if (--m_readers < 0 && --m_holdouts == 0)
{
m_writerSem.Release();
}
}
void ReaderWriterLock::LockWriter()
{
m_writerLock.lock();
if(const auto current = m_readers.fetch_sub(MaxReaders))
{
assert(current > 0);
const auto holdouts = m_holdouts.fetch_add(current) + current;
assert(holdouts >= 0);
if(holdouts > 0)
{
m_writerSem.WaitOne();
}
}
}
void ReaderWriterLock::UnlockWriter()
{
assert(m_holdouts == 0);
const auto current = m_readers.fetch_add(MaxReaders) + MaxReaders;
assert(current >= 0);
for(int64_t r = 0; r < current; r++)
{
m_readerSem.Release();
}
m_writerLock.unlock();
}
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