threadLocalScopedCache.h

//
// Copyright 2016 Pixar
//
// Licensed under the terms set forth in the LICENSE.txt file available at
// https://openusd.org/license.
//
#ifndef PXR_USD_AR_THREAD_LOCAL_SCOPED_CACHE_H
#define PXR_USD_AR_THREAD_LOCAL_SCOPED_CACHE_H
 
#include "pxr/pxr.h"
#include "pxr/usd/ar/api.h"
 
#include "pxr/base/vt/value.h"
#include "pxr/base/tf/diagnostic.h"
 
#include <tbb/enumerable_thread_specific.h>
#include <memory>
#include <vector>
 
PXR_NAMESPACE_OPEN_SCOPE
 
template <class CachedType>
class ArThreadLocalScopedCache
{
public:
    using CachePtr = std::shared_ptr<CachedType>;
 
    void BeginCacheScope(VtValue* cacheScopeData)
    {
        // Since this is intended to be used by ArResolver implementations,
        // we expect cacheScopeData to never be NULL and to either be empty
        // or holding a cache pointer that we've filled in previously.
        if (!cacheScopeData ||
            (!cacheScopeData->IsEmpty() &&
             !cacheScopeData->IsHolding<CachePtr>())) {
            TF_CODING_ERROR("Unexpected cache scope data");
            return;
        }
 
        _CachePtrStack& cacheStack = _threadCacheStack.local();
        if (cacheScopeData->IsHolding<CachePtr>()) {
            cacheStack.push_back(cacheScopeData->UncheckedGet<CachePtr>());
        }
        else {
            if (cacheStack.empty()) {
                cacheStack.push_back(std::make_shared<CachedType>());
            }
            else {
                cacheStack.push_back(cacheStack.back());
            }
        }
        *cacheScopeData = cacheStack.back();
    }
 
    void EndCacheScope(VtValue* cacheScopeData)
    {
        _CachePtrStack& cacheStack = _threadCacheStack.local();
        if (TF_VERIFY(!cacheStack.empty())) {
            cacheStack.pop_back();
        }
    }
 
    CachePtr GetCurrentCache()
    {
        _CachePtrStack& cacheStack = _threadCacheStack.local();
        return (cacheStack.empty() ? CachePtr() : cacheStack.back());
    }
 
private:
    using _CachePtrStack = std::vector<CachePtr>;
    using _ThreadLocalCachePtrStack = 
        tbb::enumerable_thread_specific<_CachePtrStack>;
    _ThreadLocalCachePtrStack _threadCacheStack;
};
 
PXR_NAMESPACE_CLOSE_SCOPE
 
#endif // PXR_USD_AR_THREAD_LOCAL_SCOPED_CACHE_H