stageCacheContext.h

//
// Copyright 2016 Pixar
//
// Licensed under the terms set forth in the LICENSE.txt file available at
// https://openusd.org/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