ClickHouse/libs/libcommon/include/common/DateLUT.h

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#pragma once
#include <common/DateLUTImpl.h>
#include <common/singleton.h>
#include <DB/Core/Defines.h>
#include <unordered_map>
#include <atomic>
#include <mutex>
#include <memory>
/// This class provides lazy initialization and lookup of singleton DateLUTImpl objects for a given timezone.
class DateLUT : public Singleton<DateLUT>
{
friend class Singleton<DateLUT>;
public:
DateLUT(const DateLUT &) = delete;
DateLUT & operator=(const DateLUT &) = delete;
/// Return singleton DateLUTImpl instance for the default time zone.
static ALWAYS_INLINE const DateLUTImpl & instance()
{
const auto & date_lut = Singleton<DateLUT>::instance();
return *date_lut.default_impl.load(std::memory_order_acquire);
}
/// Return singleton DateLUTImpl instance for a given time zone.
static ALWAYS_INLINE const DateLUTImpl & instance(const std::string & time_zone)
{
const auto & date_lut = Singleton<DateLUT>::instance();
if (time_zone.empty())
return *date_lut.default_impl.load(std::memory_order_acquire);
return date_lut.getImplementation(time_zone);
}
static void setDefaultTimezone(const std::string & time_zone)
{
auto & date_lut = Singleton<DateLUT>::instance();
const auto & impl = date_lut.getImplementation(time_zone);
date_lut.default_impl.store(&impl, std::memory_order_release);
}
protected:
DateLUT();
private:
const DateLUTImpl & getImplementation(const std::string & time_zone) const;
using DateLUTImplPtr = std::unique_ptr<DateLUTImpl>;
/// Time zone name -> implementation.
mutable std::unordered_map<std::string, DateLUTImplPtr> impls;
mutable std::mutex mutex;
std::atomic<const DateLUTImpl *> default_impl;
};