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/*
* Copyright 2019-2021 Diligent Graphics LLC
* Copyright 2015-2019 Egor Yusov
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*
* In no event and under no legal theory, whether in tort (including negligence),
* contract, or otherwise, unless required by applicable law (such as deliberate
* and grossly negligent acts) or agreed to in writing, shall any Contributor be
* liable for any damages, including any direct, indirect, special, incidental,
* or consequential damages of any character arising as a result of this License or
* out of the use or inability to use the software (including but not limited to damages
* for loss of goodwill, work stoppage, computer failure or malfunction, or any and
* all other commercial damages or losses), even if such Contributor has been advised
* of the possibility of such damages.
*/
#pragma once
#include "../../Platforms/interface/Atomics.hpp"
#include "../../Platforms/Basic/interface/DebugUtilities.hpp"
namespace ThreadingTools
{
class LockFlag
{
public:
enum
{
LOCK_FLAG_UNLOCKED = 0,
LOCK_FLAG_LOCKED = 1
};
LockFlag(Atomics::Long InitFlag = LOCK_FLAG_UNLOCKED) noexcept
{
//m_Flag.store(InitFlag);
m_Flag = InitFlag;
}
operator Atomics::Long() const { return m_Flag; }
private:
friend class LockHelper;
Atomics::AtomicLong m_Flag;
};
// Spinlock implementation. This kind of lock should be used in scenarios
// where simultaneous access is uncommon but possible.
class LockHelper
{
public:
LockHelper() noexcept {}
LockHelper(LockFlag& LockFlag) noexcept
{
Lock(LockFlag);
}
LockHelper(LockHelper&& LockHelper) noexcept :
m_pLockFlag{std::move(LockHelper.m_pLockFlag)}
{
LockHelper.m_pLockFlag = nullptr;
}
const LockHelper& operator=(LockHelper&& LockHelper) noexcept
{
m_pLockFlag = std::move(LockHelper.m_pLockFlag);
LockHelper.m_pLockFlag = nullptr;
return *this;
}
~LockHelper()
{
Unlock();
}
static bool UnsafeTryLock(LockFlag& LockFlag) noexcept
{
return Atomics::AtomicCompareExchange(LockFlag.m_Flag,
static_cast<Atomics::Long>(LockFlag::LOCK_FLAG_LOCKED),
static_cast<Atomics::Long>(LockFlag::LOCK_FLAG_UNLOCKED)) == LockFlag::LOCK_FLAG_UNLOCKED;
}
bool TryLock(LockFlag& LockFlag) noexcept
{
if (UnsafeTryLock(LockFlag))
{
m_pLockFlag = &LockFlag;
return true;
}
else
return false;
}
static constexpr const int DefaultSpinCountToYield = 256;
static void UnsafeLock(LockFlag& LockFlag, int SpinCountToYield = DefaultSpinCountToYield) noexcept
{
int SpinCount = 0;
while (!UnsafeTryLock(LockFlag))
{
++SpinCount;
if (SpinCount == SpinCountToYield)
{
SpinCount = 0;
YieldThread();
}
}
}
void Lock(LockFlag& LockFlag, int SpinCountToYield = DefaultSpinCountToYield) noexcept
{
VERIFY(m_pLockFlag == NULL, "Object already locked");
// Wait for the flag to become unlocked and lock it
int SpinCount = 0;
while (!TryLock(LockFlag))
{
++SpinCount;
if (SpinCount == SpinCountToYield)
{
SpinCount = 0;
YieldThread();
}
}
}
static void UnsafeUnlock(LockFlag& LockFlag) noexcept
{
LockFlag.m_Flag = LockFlag::LOCK_FLAG_UNLOCKED;
}
void Unlock() noexcept
{
if (m_pLockFlag)
UnsafeUnlock(*m_pLockFlag);
m_pLockFlag = NULL;
}
private:
static void YieldThread() noexcept;
LockFlag* m_pLockFlag = nullptr;
// clang-format off
LockHelper (const LockHelper& LockHelper) = delete;
LockHelper& operator=(const LockHelper& LockHelper) = delete;
// clang-format on
};
} // namespace ThreadingTools
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