envSetting.h

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//
// Copyright 2016 Pixar
//
// Licensed under the terms set forth in the LICENSE.txt file available at
// https://openusd.org/license.
//
#ifndef PXR_BASE_TF_ENV_SETTING_H
#define PXR_BASE_TF_ENV_SETTING_H
 
 
#include "pxr/pxr.h"
#include "pxr/base/arch/hints.h"
#include "pxr/base/tf/registryManager.h"
 
#include <atomic>
#include <string>
 
PXR_NAMESPACE_OPEN_SCOPE
 
// POD, statically initialized.
//
// We store the atomic_value separately and refer to it via pointer because we
// cannot use aggregate-initialization on a struct holding an atomic, but we
// can value-initialize a single std::atomic.
template <class T>
struct TfEnvSetting
{
    std::atomic<T*> *_value;
    T _default;
    char const * _name;
    char const * _description;
};
 
// Specialize for string, default is stored as char const * (pointing to a
// literal).
template <>
struct TfEnvSetting<std::string>
{
    std::atomic<std::string*> *_value;
    char const * _default;
    char const * _name;
    char const * _description;
};
 
template <class T>
void Tf_InitializeEnvSetting(TfEnvSetting<T> *);
 
template <class T>
inline T const &
TfGetEnvSetting(TfEnvSetting<T>& setting) {
    T *val = setting._value->load();
    if (ARCH_UNLIKELY(!val)) {
        Tf_InitializeEnvSetting(&setting);
        val = setting._value->load();
    }
    return *val;
}
 
// Ensure that we only allow bool, int, and string, and map char * and char
// array to string.
 
bool Tf_ChooseEnvSettingType(bool);
int Tf_ChooseEnvSettingType(int);
std::string Tf_ChooseEnvSettingType(char const *);
 
class Tf_EnvSettingRegistry;
 
#define TF_DEFINE_ENV_SETTING(envVar, defValue, description)                  \
    std::atomic< decltype(Tf_ChooseEnvSettingType(defValue))*>                \
        envVar##_value;                                                       \
    TfEnvSetting<decltype(Tf_ChooseEnvSettingType(defValue))> envVar = {      \
        &envVar##_value, defValue, #envVar, description };                    \
    TF_REGISTRY_FUNCTION_WITH_TAG(Tf_EnvSettingRegistry, envVar) {            \
        (void)TfGetEnvSetting(envVar);                                        \
    }
 
PXR_NAMESPACE_CLOSE_SCOPE
 
#endif // PXR_BASE_TF_ENV_SETTING_H