spinMutex.h

//
// Copyright 2023 Pixar
//
// Licensed under the Apache License, Version 2.0 (the "Apache License")
// with the following modification; you may not use this file except in
// compliance with the Apache License and the following modification to it:
// Section 6. Trademarks. is deleted and replaced with:
//
// 6. Trademarks. This License does not grant permission to use the trade
//    names, trademarks, service marks, or product names of the Licensor
//    and its affiliates, except as required to comply with Section 4(c) of
//    the License and to reproduce the content of the NOTICE file.
//
// You may obtain a copy of the Apache License at
//
//     http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the Apache License with the above modification is
// distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
// KIND, either express or implied. See the Apache License for the specific
// language governing permissions and limitations under the Apache License.
//
#ifndef PXR_BASE_TF_SPIN_MUTEX_H
#define PXR_BASE_TF_SPIN_MUTEX_H
 
#include "pxr/pxr.h"
#include "pxr/base/tf/api.h"
 
#include "pxr/base/arch/hints.h"
#include "pxr/base/tf/diagnosticLite.h"
 
#include <atomic>
 
PXR_NAMESPACE_OPEN_SCOPE
 
class TfSpinMutex
{
public:
 
    TfSpinMutex() : _lockState(false) {}
 
    struct ScopedLock {
 
        explicit ScopedLock(TfSpinMutex &m)
            : _mutex(&m)
            , _acquired(false) {
            Acquire();
        }
 
        ScopedLock() : _mutex(nullptr), _acquired(false) {}
 
        ~ScopedLock() {
            Release();
        }
 
        void Acquire(TfSpinMutex &m) {
            Release();
            _mutex = &m;
            Acquire();
        }            
 
        void Release() {
            if (_acquired) {
                _Release();
            }
        }
        
        void Acquire() {
            TF_DEV_AXIOM(!_acquired);
            _mutex->Acquire();
            _acquired = true;
        }
 
    private:
 
        void _Release() {
            TF_DEV_AXIOM(_acquired);
            _mutex->Release();
            _acquired = false;
        }
 
        TfSpinMutex *_mutex;
        bool _acquired;
    };
 
    inline bool TryAcquire() {
        return _lockState.exchange(true, std::memory_order_acquire) == false;
    }
 
    void Acquire() {
        if (ARCH_LIKELY(TryAcquire())) {
            return;
        }
        _AcquireContended();
    }
 
    inline void Release() {
        _lockState.store(false, std::memory_order_release);
    }
 
private:
    
    TF_API void _AcquireContended();
    
    std::atomic<bool> _lockState;
};
 
PXR_NAMESPACE_CLOSE_SCOPE
 
#endif // PXR_BASE_TF_SPIN_MUTEX_H