util/thread/singleton.h


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#pragma once

#include <util/system/tls.h>
#include <util/generic/singleton.h>
#include <util/generic/ptr.h>

namespace NPrivate { 
    template <class T, size_t Priority> 
    struct TFastThreadSingletonHelper { 
        static inline T* GetSlow() { 
            return SingletonWithPriority<NTls::TValue<T>, Priority>()->GetPtr(); 
        } 

        static inline T* Get() { 
#if defined(Y_HAVE_FAST_POD_TLS)
            Y_POD_STATIC_THREAD(T*) fast(nullptr); 

            if (Y_UNLIKELY(!fast)) {
                fast = GetSlow(); 
            } 
 
            return fast; 
#else 
            return GetSlow(); 
#endif 
        } 
    }; 
}

template <class T, size_t Priority> 
static inline T* FastTlsSingletonWithPriority() { 
    return ::NPrivate::TFastThreadSingletonHelper<T, Priority>::Get(); 
}

// NB: the singleton is the same for all modules that use
// FastTlsSingleton with the same type parameter. If unique singleton
// required, use unique types.
template <class T> 
static inline T* FastTlsSingleton() { 
    return FastTlsSingletonWithPriority<T, TSingletonTraits<T>::Priority>(); 
}