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#pragma once
#include <library/cpp/yt/memory/erased_storage.h>
#include <library/cpp/yt/misc/strong_typedef.h>
#include <atomic>
namespace NYT::NGlobal {
////////////////////////////////////////////////////////////////////////////////
namespace NDetail {
class TGlobalVariablesRegistry;
} // namespace NDetail
////////////////////////////////////////////////////////////////////////////////
inline constexpr size_t GlobalVariableMaxByteSize = 32;
using TErasedStorage = NYT::TErasedStorage<GlobalVariableMaxByteSize>;
// NB(arkady-e1ppa): Accessor must ensure thread-safety on its own.
using TAccessor = TErasedStorage(*)() noexcept;
////////////////////////////////////////////////////////////////////////////////
// Usage:
/*
* // public.h file:
* // NB: It's important to mark it inline for linker to deduplicate
* // addresses accross different UT's.
* inline constexpr NGlobal::TVariableTag MyGlobalVarTag = {};
*
*
*
* // some_stuff.cpp file
*
* TErasedStorage GetMyVar()
* {
* // definition here
* }
* NGlobal::Variable<int> MyGlobalVar{MyGlobalVarTag, &GetMyVar};
*
*
*
* // other_stuff.cpp file
*
*
* int ReadMyVar()
* {
* auto erased = NGlobal::GetErasedVariable(MyGlobalVarTag);
* return erased->AsConcrete<int>();
* }
*/
class TVariableTag
{
public:
TVariableTag() = default;
TVariableTag(const TVariableTag& other) = delete;
TVariableTag& operator=(const TVariableTag& other) = delete;
private:
friend class ::NYT::NGlobal::NDetail::TGlobalVariablesRegistry;
mutable std::atomic<bool> Initialized_ = false;
mutable std::atomic<int> Key_ = -1;
};
////////////////////////////////////////////////////////////////////////////////
// Defined in impl.cpp.
// |std::nullopt| iff global variable with a given tag is not present.
std::optional<TErasedStorage> GetErasedVariable(const TVariableTag& tag);
////////////////////////////////////////////////////////////////////////////////
} // namespace NYT::NGlobal
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