OperationQueue.h

#pragma once
 
/* <editor-fold desc="MIT License">
 
Copyright(c) 2018 Robert Osfield
 
Permission is hereby granted, free of charge, to any person obtaining a copy of this software and associated documentation files (the "Software"), to deal in the Software without restriction, including without limitation the rights to use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies of the Software, and to permit persons to whom the Software is furnished to do so, subject to the following conditions:
 
The above copyright notice and this permission notice shall be included in all copies or substantial portions of the Software.
 
THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
 
</editor-fold> */
 
#include <vsg/io/Logger.h>
#include <vsg/threading/ActivityStatus.h>
#include <vsg/threading/Latch.h>
 
#include <list>
 
namespace vsg
{
    enum InsertionPosition
    {
        INSERT_FRONT,
        INSERT_BACK
    };

    template<class T>
    class ThreadSafeQueue : public Inherit<Object, ThreadSafeQueue<T>>
    {
    public:
        using value_type = T;
        using container_type = std::list<value_type>;
 
        explicit ThreadSafeQueue(ref_ptr<ActivityStatus> status) :
            _status(status)
        {
        }
 
        ActivityStatus* getStatus() { return _status; }
        const ActivityStatus* getStatus() const { return _status; }

        void add(value_type operation, InsertionPosition insertionPosition = INSERT_BACK)
        {
            std::scoped_lock lock(_mutex);
            if (insertionPosition == INSERT_BACK)
                _queue.emplace_back(operation);
            else
                _queue.emplace_front(operation);
            _cv.notify_one();
        }

        template<typename Iterator>
        void add(Iterator begin, Iterator end, InsertionPosition insertionPosition = INSERT_BACK)
        {
            size_t numAdditions = 0;
            std::scoped_lock lock(_mutex);
            for (auto itr = begin; itr != end; ++itr)
            {
                if (insertionPosition == INSERT_BACK)
                    _queue.emplace_back(*itr);
                else
                    _queue.emplace_front(*itr);
                ++numAdditions;
            }
 
            if (numAdditions == 1)
                _cv.notify_one();
            else if (numAdditions > 1)
                _cv.notify_all();
        }

        bool empty() const
        {
            std::unique_lock lock(_mutex);
            return _queue.empty();
        }

        container_type take_all()
        {
            std::unique_lock lock(_mutex);
 
            container_type objects;
            objects.swap(_queue);
 
            return objects;
        }

        value_type take()
        {
            std::unique_lock lock(_mutex);
 
            if (_queue.empty()) return {};
 
            auto operation = _queue.front();
 
            _queue.erase(_queue.begin());
 
            return operation;
        }

        value_type take_when_available()
        {
            std::chrono::duration waitDuration = std::chrono::milliseconds(100);
 
            std::unique_lock lock(_mutex);
 
            // wait until the conditional variable signals that an operation has been added
            while (_queue.empty() && _status->active())
            {
                // debug("Waiting on condition variable");
                _cv.wait_for(lock, waitDuration);
            }
 
            // if the threads we are associated with should no longer be running go for a quick exit and return nothing.
            if (_status->cancel())
            {
                return {};
            }
 
            // remove and return the head of the queue
            auto operation = _queue.front();
            _queue.erase(_queue.begin());
            return operation;
        }
 
    protected:
        mutable std::mutex _mutex;
        std::condition_variable _cv;
        container_type _queue;
        ref_ptr<ActivityStatus> _status;
    };
 
    // clang-format screws up handling of VSG_type_name macro so have to switch it off.
    // clang-format off

    struct Operation : public Object
    {
        virtual void run() = 0;
    };
    VSG_type_name(vsg::Operation)
 
    
    using OperationQueue = ThreadSafeQueue<ref_ptr<Operation>>;
    VSG_type_name(vsg::OperationQueue)
 
} // namespace vsg