WorkQueue.hpp

//------------------------------------------------------------------------------
/*
    This file is part of clio: https://github.com/XRPLF/clio
    Copyright (c) 2022, the clio developers.
 
    Permission to use, copy, modify, and distribute this software for any
    purpose with or without fee is hereby granted, provided that the above
    copyright notice and this permission notice appear in all copies.
 
    THE  SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
    WITH  REGARD  TO  THIS  SOFTWARE  INCLUDING  ALL  IMPLIED  WARRANTIES  OF
    MERCHANTABILITY  AND  FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
    ANY  SPECIAL,  DIRECT,  INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
    WHATSOEVER  RESULTING  FROM  LOSS  OF USE, DATA OR PROFITS, WHETHER IN AN
    ACTION  OF  CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
    OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
*/
//==============================================================================
 
#pragma once
 
#include "util/Mutex.hpp"
#include "util/config/ConfigDefinition.hpp"
#include "util/log/Logger.hpp"
#include "util/prometheus/Counter.hpp"
#include "util/prometheus/Gauge.hpp"
 
#include <boost/asio/spawn.hpp>
#include <boost/asio/thread_pool.hpp>
#include <boost/json/object.hpp>
 
#include <atomic>
#include <chrono>
#include <cstddef>
#include <cstdint>
#include <functional>
#include <limits>
#include <optional>
#include <queue>
#include <utility>
 
namespace rpc {

struct Reportable {
    virtual ~Reportable() = default;

    [[nodiscard]] virtual boost::json::object
    report() const = 0;
};

class WorkQueue : public Reportable {
    using TaskType = std::function<void(boost::asio::yield_context)>;
 
    struct TaskWithTimestamp {
        TaskType task;
        std::chrono::system_clock::time_point queuedAt;
    };
 
    using QueueType = std::queue<TaskWithTimestamp>;
 
public:
    enum class Priority : uint8_t {
        High,
        Default,
    };
 
private:
    struct QueueState {
        QueueType high;
        QueueType normal;
 
        size_t highPriorityCounter = 0;
 
        void
        push(Priority priority, TaskType&& task)
        {
            auto& queue = [this, priority] -> QueueType& {
                if (priority == Priority::High)
                    return high;
                return normal;
            }();
            queue.push(
                TaskWithTimestamp{
                    .task = std::move(task), .queuedAt = std::chrono::system_clock::now()
                }
            );
        }
 
        [[nodiscard]] bool
        empty() const
        {
            return high.empty() and normal.empty();
        }
 
        [[nodiscard]] std::optional<TaskWithTimestamp>
        popNext()
        {
            if (not high.empty() and (highPriorityCounter < kTAKE_HIGH_PRIO or normal.empty())) {
                auto taskWithTimestamp = std::move(high.front());
                high.pop();
                ++highPriorityCounter;
                return taskWithTimestamp;
            }
 
            if (not normal.empty()) {
                auto taskWithTimestamp = std::move(normal.front());
                normal.pop();
                highPriorityCounter = 0;
                return taskWithTimestamp;
            }
 
            return std::nullopt;
        }
    };
 
private:
    static constexpr auto kTAKE_HIGH_PRIO = 4uz;
 
    // these are cumulative for the lifetime of the process
    std::reference_wrapper<util::prometheus::CounterInt> queued_;
    std::reference_wrapper<util::prometheus::CounterInt> durationUs_;
 
    std::reference_wrapper<util::prometheus::GaugeInt> curSize_;
    uint32_t maxSize_ = std::numeric_limits<uint32_t>::max();
 
    util::Logger log_{"RPC"};
    boost::asio::thread_pool ioc_;
 
    std::atomic_bool stopping_;
    std::atomic_bool processingStarted_{false};
 
    class OneTimeCallable {
        std::function<void()> func_;
        bool called_{false};
 
    public:
        void
        setCallable(std::function<void()> func);
 
        void
        operator()();
 
        explicit
        operator bool() const;
    };
    util::Mutex<OneTimeCallable> onQueueEmpty_;
    util::Mutex<QueueState> queueState_;
 
public:
    struct DontStartProcessingTag {};
    static constexpr DontStartProcessingTag kDONT_START_PROCESSING_TAG = {};

    WorkQueue(std::uint32_t numWorkers, uint32_t maxSize = 0);

    WorkQueue(DontStartProcessingTag, std::uint32_t numWorkers, uint32_t maxSize = 0);
 
    ~WorkQueue() override;

    void
    startProcessing();

    void
    requestStop(std::function<void()> onQueueEmpty = [] {});

    void
    stop();

    [[nodiscard]] static WorkQueue
    makeWorkQueue(util::config::ClioConfigDefinition const& config);

    bool
    postCoro(TaskType func, bool isWhiteListed, Priority priority = Priority::Default);

    [[nodiscard]] boost::json::object
    report() const override;

    void
    join();

    [[nodiscard]] size_t
    size() const;
 
private:
    void
    executeTask(boost::asio::yield_context yield);
};
 
}  // namespace rpc