fiber/examples/barrier.hpp

//          Copyright Oliver Kowalke 2013.
// Distributed under the Boost Software License, Version 1.0.
//    (See accompanying file LICENSE_1_0.txt or copy at
//          http://www.boost.org/LICENSE_1_0.txt)

#ifndef BARRIER_H
#define BARRIER_H

#include <cstddef>
#include <condition_variable>
#include <mutex>

#include <boost/assert.hpp>

class barrier {
private:
	std::size_t             initial_;
	std::size_t             current_;
	bool                    cycle_{ true };
    std::mutex              mtx_{};
    std::condition_variable cond_{};

public:
	explicit barrier( std::size_t initial) :
        initial_{ initial },
        current_{ initial_ } {
        BOOST_ASSERT ( 0 != initial);
    }

    barrier( barrier const&) = delete;
    barrier & operator=( barrier const&) = delete;

    bool wait() {
        std::unique_lock< std::mutex > lk( mtx_);
        const bool cycle = cycle_;
        if ( 0 == --current_) {
            cycle_ = ! cycle_;
            current_ = initial_;
            lk.unlock(); // no pessimization
            cond_.notify_all();
            return true;
        } else {
            cond_.wait( lk, [&](){ return cycle != cycle_; });
        }
        return false;
    }
};

#endif // BARRIER_H