mpmc_blocking_q.h

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// Copyright(c) 2015-present, Gabi Melman & spdlog contributors.
// Distributed under the MIT License (http://opensource.org/licenses/MIT)
 
#pragma once
 
// multi producer-multi consumer blocking queue.
// enqueue(..) - will block until room found to put the new message.
// enqueue_nowait(..) - will return immediately with false if no room left in
// the queue.
// dequeue_for(..) - will block until the queue is not empty or timeout have
// passed.
 
#include <spdlog/details/circular_q.h>
 
#include <condition_variable>
#include <mutex>
 
namespace spdlog
{
    namespace details
    {
 
        template <typename T>
        class mpmc_blocking_queue
        {
        public:
            using item_type = T;
            explicit mpmc_blocking_queue(size_t max_items)
                : q_(max_items)
            {
            }
 
#ifndef __MINGW32__
            // try to enqueue and block if no room left
            void enqueue(T&& item)
            {
                {
                    std::unique_lock<std::mutex> lock(queue_mutex_);
                    pop_cv_.wait(lock, [this] { return !this->q_.full(); });
                    q_.push_back(std::move(item));
                }
                push_cv_.notify_one();
            }
 
            // enqueue immediately. overrun oldest message in the queue if no room left.
            void enqueue_nowait(T&& item)
            {
                {
                    std::unique_lock<std::mutex> lock(queue_mutex_);
                    q_.push_back(std::move(item));
                }
                push_cv_.notify_one();
            }
 
            // dequeue with a timeout.
            // Return true, if succeeded dequeue item, false otherwise
            bool dequeue_for(T& popped_item, std::chrono::milliseconds wait_duration)
            {
                {
                    std::unique_lock<std::mutex> lock(queue_mutex_);
                    if (!push_cv_.wait_for(lock, wait_duration, [this] { return !this->q_.empty(); }))
                    {
                        return false;
                    }
                    popped_item = std::move(q_.front());
                    q_.pop_front();
                }
                pop_cv_.notify_one();
                return true;
            }
 
            // blocking dequeue without a timeout.
            void dequeue(T& popped_item)
            {
                {
                    std::unique_lock<std::mutex> lock(queue_mutex_);
                    push_cv_.wait(lock, [this] { return !this->q_.empty(); });
                    popped_item = std::move(q_.front());
                    q_.pop_front();
                }
                pop_cv_.notify_one();
            }
 
#else
            // apparently mingw deadlocks if the mutex is released before cv.notify_one(),
            // so release the mutex at the very end each function.
 
            // try to enqueue and block if no room left
            void enqueue(T&& item)
            {
                std::unique_lock<std::mutex> lock(queue_mutex_);
                pop_cv_.wait(lock, [this] { return !this->q_.full(); });
                q_.push_back(std::move(item));
                push_cv_.notify_one();
            }
 
            // enqueue immediately. overrun oldest message in the queue if no room left.
            void enqueue_nowait(T&& item)
            {
                std::unique_lock<std::mutex> lock(queue_mutex_);
                q_.push_back(std::move(item));
                push_cv_.notify_one();
            }
 
            // dequeue with a timeout.
            // Return true, if succeeded dequeue item, false otherwise
            bool dequeue_for(T& popped_item, std::chrono::milliseconds wait_duration)
            {
                std::unique_lock<std::mutex> lock(queue_mutex_);
                if (!push_cv_.wait_for(lock, wait_duration, [this] { return !this->q_.empty(); }))
                {
                    return false;
                }
                popped_item = std::move(q_.front());
                q_.pop_front();
                pop_cv_.notify_one();
                return true;
            }
 
            // blocking dequeue without a timeout.
            void dequeue(T& popped_item)
            {
                std::unique_lock<std::mutex> lock(queue_mutex_);
                push_cv_.wait(lock, [this] { return !this->q_.empty(); });
                popped_item = std::move(q_.front());
                q_.pop_front();
                pop_cv_.notify_one();
            }
 
#endif
 
            size_t overrun_counter()
            {
                std::unique_lock<std::mutex> lock(queue_mutex_);
                return q_.overrun_counter();
            }
 
            size_t size()
            {
                std::unique_lock<std::mutex> lock(queue_mutex_);
                return q_.size();
            }
 
            void reset_overrun_counter()
            {
                std::unique_lock<std::mutex> lock(queue_mutex_);
                q_.reset_overrun_counter();
            }
 
        private:
            std::mutex                     queue_mutex_;
            std::condition_variable        push_cv_;
            std::condition_variable        pop_cv_;
            spdlog::details::circular_q<T> q_;
        };
    } // namespace details
} // namespace spdlog