staticData.h

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//
// Copyright 2016 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_STATIC_DATA_H
#define PXR_BASE_TF_STATIC_DATA_H


#include "pxr/pxr.h"
#include "pxr/base/arch/hints.h"
#include "pxr/base/tf/preprocessorUtils.h"
#include "pxr/base/tf/preprocessorUtilsLite.h"

#include <atomic>
#include <type_traits>

PXR_NAMESPACE_OPEN_SCOPE

template <class T>
struct Tf_StaticDataDefaultFactory {
    static T *New() { return new T; }
};

template <class T, class Factory = Tf_StaticDataDefaultFactory<T> >
class TfStaticData {
public:
    inline T* operator-> () const { return Get(); }

    inline T& operator* () const { return *Get(); }

    inline T* Get() const {
        T *p = _data;
        return ARCH_LIKELY(p) ? p : _TryToCreateData();
    }
    
    inline bool IsInitialized() const { return _data.load() != nullptr; }

private:
    T *_TryToCreateData() const {
        // Allocate an instance.
        T *tmp = Factory::New();

        // Try to atomically set the pointer from null to tmp.
        T *n = nullptr;
        if (ARCH_LIKELY(_data.compare_exchange_strong(n, tmp)))
            return tmp;

        // Another thread won the initialization race.
        delete tmp;
        return _data;
    }

    mutable std::atomic<T *> _data;
};

#define TF_MAKE_STATIC_DATA(Type, Name)                                        \
    static void TF_PP_CAT(Name,_Tf_StaticDataFactoryImpl)(                     \
        std::remove_const_t<TF_PP_EAT_PARENS(Type)> *);                        \
    namespace {                                                                \
    struct TF_PP_CAT(Name,_Tf_StaticDataFactory) {                             \
        static TF_PP_EAT_PARENS(Type) *New() {                                 \
            auto *p = new std::remove_const_t<TF_PP_EAT_PARENS(Type)>;         \
            TF_PP_CAT(Name,_Tf_StaticDataFactoryImpl)(p);                      \
            return p;                                                          \
        }                                                                      \
    };                                                                         \
    }                                                                          \
    static TfStaticData<                                                       \
        TF_PP_EAT_PARENS(Type), TF_PP_CAT(Name,_Tf_StaticDataFactory)> Name;   \
    static void TF_PP_CAT(Name,_Tf_StaticDataFactoryImpl)(                     \
        std::remove_const_t<TF_PP_EAT_PARENS(Type)> *Name)

PXR_NAMESPACE_CLOSE_SCOPE

#endif