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/* Icinga 2 | (c) 2019 Icinga GmbH | GPLv2+ */
#ifndef ATOMIC_H
#define ATOMIC_H
#include <atomic>
#include <chrono>
#include <mutex>
#include <type_traits>
#include <utility>
namespace icinga
{
/**
* Like std::atomic, but enforces usage of its only safe constructor.
*
* "The default-initialized std::atomic<T> does not contain a T object,
* and its only valid uses are destruction and
* initialization by std::atomic_init, see LWG issue 2334."
* -- https://en.cppreference.com/w/cpp/atomic/atomic/atomic
*
* @ingroup base
*/
template<class T>
class Atomic : public std::atomic<T> {
public:
/**
* The only safe constructor of std::atomic#atomic
*
* @param desired Initial value
*/
inline Atomic(T desired) : std::atomic<T>(desired)
{
}
};
/**
* Accumulates time durations atomically.
*
* @ingroup base
*/
class AtomicDuration
{
public:
using Clock = std::chrono::steady_clock;
/**
* Adds the elapsedTime to this instance.
*
* May be called multiple times to accumulate time.
*
* @param elapsedTime The distance between two time points
*
* @return This instance for method chaining
*/
AtomicDuration& operator+=(const Clock::duration& elapsedTime) noexcept
{
m_Sum.fetch_add(elapsedTime.count(), std::memory_order_relaxed);
return *this;
}
/**
* @return The total accumulated time in seconds
*/
operator double() const noexcept
{
return std::chrono::duration<double>(Clock::duration(m_Sum.load(std::memory_order_relaxed))).count();
}
private:
Atomic<Clock::duration::rep> m_Sum {0};
};
/**
* Wraps any T into a std::atomic<T>-like interface that locks using a mutex.
*
* In contrast to std::atomic<T>, Locked<T> is also valid for types that are not trivially copyable.
* In case T is trivially copyable, std::atomic<T> is almost certainly the better choice.
*
* @ingroup base
*/
template<typename T>
class Locked
{
public:
inline T load() const
{
std::unique_lock<std::mutex> lock(m_Mutex);
return m_Value;
}
inline void store(T desired)
{
std::unique_lock<std::mutex> lock(m_Mutex);
m_Value = std::move(desired);
}
private:
mutable std::mutex m_Mutex;
T m_Value;
};
/**
* Type alias for std::atomic<T> if possible, otherwise Locked<T> is used as a fallback.
*
* @ingroup base
*/
template <typename T>
using AtomicOrLocked =
#if defined(__GNUC__) && __GNUC__ < 5
// GCC does not implement std::is_trivially_copyable until version 5.
typename std::conditional<std::is_fundamental<T>::value || std::is_pointer<T>::value, std::atomic<T>, Locked<T>>::type;
#else /* defined(__GNUC__) && __GNUC__ < 5 */
typename std::conditional<std::is_trivially_copyable<T>::value, std::atomic<T>, Locked<T>>::type;
#endif /* defined(__GNUC__) && __GNUC__ < 5 */
}
#endif /* ATOMIC_H */
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