easy_profiler/src/spin_lock.h

/**
Lightweight profiler library for c++
Copyright(C) 2016  Sergey Yagovtsev

This program is free software : you can redistribute it and / or modify
it under the terms of the GNU General Public License as published by
the Free Software Foundation, either version 3 of the License, or
(at your option) any later version.

This program is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.See the
GNU General Public License for more details.

You should have received a copy of the GNU General Public License
along with this program.If not, see <http://www.gnu.org/licenses/>.
**/

#ifndef EASY_PROFILER__SPIN_LOCK__________H______
#define EASY_PROFILER__SPIN_LOCK__________H______

#define EASY_USE_CRITICAL_SECTION // Use CRITICAL_SECTION instead of std::atomic_flag

#if defined(_WIN32) && defined(EASY_USE_CRITICAL_SECTION)
#include <Windows.h>
#else
#include <atomic>
#endif

namespace profiler {

#if defined(_WIN32) && defined(EASY_USE_CRITICAL_SECTION)
    // std::atomic_flag on Windows works slower than critical section, so we will use it instead of std::atomic_flag...
    // By the way, Windows critical sections are slower than std::atomic_flag on Unix.
    class spin_lock { CRITICAL_SECTION m_lock; public:

        void lock() {
            EnterCriticalSection(&m_lock);
        }

        void unlock() {
            LeaveCriticalSection(&m_lock);
        }

        spin_lock() {
            InitializeCriticalSection(&m_lock);
        }

        ~spin_lock() {
            DeleteCriticalSection(&m_lock);
        }
    };
#else
    // std::atomic_flag on Unix works fine and very fast (almost instant!)
    class spin_lock { ::std::atomic_flag m_lock; public:

        void lock() {
            while (m_lock.test_and_set(::std::memory_order_acquire));
        }

        void unlock() {
            m_lock.clear(::std::memory_order_release);
        }

        spin_lock() {
            m_lock.clear();
        }
    };
#endif

    template <class T>
    class guard_lock
    {
        T& m_lock;
        bool m_isLocked = false;

    public:

        explicit guard_lock(T& m) : m_lock(m) {
            m_lock.lock();
            m_isLocked = true;
        }

        ~guard_lock() {
            unlock();
        }

        inline void unlock() {
            if (m_isLocked) {
                m_lock.unlock();
                m_isLocked = false;
            }
        }
    };

} // END of namespace profiler.

#ifdef EASY_USE_CRITICAL_SECTION
# undef EASY_USE_CRITICAL_SECTION
#endif

#endif // EASY_PROFILER__SPIN_LOCK__________H______