stageCacheContext.h

//
// 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_USD_USD_STAGE_CACHE_CONTEXT_H
#define PXR_USD_USD_STAGE_CACHE_CONTEXT_H

#include "pxr/pxr.h"
#include "pxr/usd/usd/api.h"
#include "pxr/base/tf/stacked.h"

#include <vector>

PXR_NAMESPACE_OPEN_SCOPE


class UsdStageCache;

// Private helper wrapper class, holds a const reference to a stage cache.
struct Usd_NonPopulatingStageCacheWrapper {
    explicit Usd_NonPopulatingStageCacheWrapper(const UsdStageCache &cache)
        : cache(cache) {}
    const UsdStageCache &cache;
};

// Using a template arg for 'cache' in UsdUseButDoNotPopulateCache enforces
// lvalue requirement: rvalues will not bind to function template non-const
// reference parameters.

template <class StageCache>
Usd_NonPopulatingStageCacheWrapper
UsdUseButDoNotPopulateCache(StageCache &cache) {
    return Usd_NonPopulatingStageCacheWrapper(cache);
}

enum UsdStageCacheContextBlockType
{
    UsdBlockStageCaches,
    UsdBlockStageCachePopulation,

    Usd_NoBlock
};

TF_DEFINE_STACKED(UsdStageCacheContext, true, USD_API)
{
public:
    explicit UsdStageCacheContext(UsdStageCache &cache)
        : _rwCache(&cache)
        , _isReadOnlyCache(false)
        , _blockType(Usd_NoBlock) {}

    explicit UsdStageCacheContext(Usd_NonPopulatingStageCacheWrapper holder)
        : _roCache(&holder.cache)
        , _isReadOnlyCache(true)
        , _blockType(Usd_NoBlock) {}

    explicit UsdStageCacheContext(UsdStageCacheContextBlockType blockType)
        : _blockType(blockType) {}

private:
    friend class UsdStage;

    static std::vector<const UsdStageCache *> _GetReadOnlyCaches();
    static std::vector<const UsdStageCache *> _GetReadableCaches();
    static std::vector<UsdStageCache *> _GetWritableCaches();

    // A blocking context is encoded with both members variables null.
    union {
        UsdStageCache *_rwCache;
        const UsdStageCache *_roCache;
    };
    bool _isReadOnlyCache;
    UsdStageCacheContextBlockType _blockType;
};


PXR_NAMESPACE_CLOSE_SCOPE

#endif // PXR_USD_USD_STAGE_CACHE_CONTEXT_H