root/ROOT/TSpinMutex.hxx

0001 // @(#)root/thread
0002 // Author: Danilo Piparo, 2016
0003
0004 /*************************************************************************
0005  * Copyright (C) 1995-2000, Rene Brun and Fons Rademakers.               *
0006  * All rights reserved.                                                  *
0007  *                                                                       *
0008  * For the licensing terms see $ROOTSYS/LICENSE.                         *
0009  * For the list of contributors see $ROOTSYS/README/CREDITS.             *
0010  *************************************************************************/
0011
0012 #ifndef ROOT_TSpinMutex
0013 #define ROOT_TSpinMutex
0014
0015 #include <atomic>
0016
0017 namespace ROOT {
0018
0019    /**
0020     * \class ROOT::TSpinMutex
0021     * \brief A spin mutex class which respects the STL interface for mutexes.
0022     * \ingroup Parallelism
0023     * This class allows to acquire spin locks also in combination with templates in the STL such as
0024     * <a href="http://en.cppreference.com/w/cpp/thread/unique_lock">std::unique_lock</a> or
0025     * <a href="http://en.cppreference.com/w/cpp/thread/condition_variable_any">std::condition_variable_any</a>.
0026     * For example:
0027     *
0028     * ~~~ {.cpp}
0029     * ROOT::TSpinMutex m;
0030     * std::condition_variable cv;
0031     * bool ready = false;
0032     *
0033     * void worker_thread()
0034     * {
0035     *    // Wait until main() sends data
0036     *    std::unique_lock<ROOT::TSpinMutex> lk(m);
0037     *    cv.wait(lk, []{return ready;});
0038     *    [...]
0039     * }
0040     * ~~~ {.cpp}
0041     */
0042    class TSpinMutex {
0043
0044    private:
0045       std::atomic_flag fAFlag = ATOMIC_FLAG_INIT;
0046
0047    public:
0048       TSpinMutex() = default;
0049       TSpinMutex(const TSpinMutex&) = delete;
0050       ~TSpinMutex() = default;
0051       TSpinMutex& operator=(const TSpinMutex&) = delete;
0052
0053       void lock() { while (fAFlag.test_and_set(std::memory_order_acquire)); }
0054       void unlock() { fAFlag.clear(std::memory_order_release); }
0055       bool try_lock() { return !fAFlag.test_and_set(std::memory_order_acquire); }
0056
0057    };
0058 }
0059
0060 #endif