simple_worker.hpp

/*
    asynchrony : Add asynchrony to your apps
 
    BSD 3-Clause License
 
    Copyright (c) 2021, Siddiq Software LLC
    All rights reserved.
 
    Redistribution and use in source and binary forms, with or without
    modification, are permitted provided that the following conditions are met:
 
    1. Redistributions of source code must retain the above copyright notice, this
       list of conditions and the following disclaimer.
 
    2. Redistributions in binary form must reproduce the above copyright notice,
       this list of conditions and the following disclaimer in the documentation
       and/or other materials provided with the distribution.
 
    3. Neither the name of the copyright holder nor the names of its
       contributors may be used to endorse or promote products derived from
       this software without specific prior written permission.
 
    THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
    AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
    IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
    DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE
    FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
    DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
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    CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
    OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
    OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 */
 
#pragma once
#include <chrono>
#ifndef SIMPLE_WORKER_HPP
#define SIMPLE_WORKER_HPP
 
 
#include <iostream>
#include <functional>
#include <memory>
#include <thread>
#include <mutex>
#include <shared_mutex>
#include <deque>
#include <semaphore>
#include <stop_token>
#include <exception>
#include <source_location>
#include <atomic>
 
#if defined(_Linux_) || defined(__linux__) || defined(__linux) || (defined(__APPLE__) && defined(__MACH__))
#include <pthread.h>
#elif defined(_WIN32) || defined(WIN32) || defined(_WIN64) || defined(WIN64)
#include <windows.h>
#include <processthreadsapi.h>
#endif
 
#include "siddiqsoft/WaitableQueue.hpp"
#include "siddiqsoft/RunOnEnd.hpp"
#include "private/common.hpp"
 
namespace siddiqsoft
{
    template <typename T, int Pri = 0>
        requires((Pri >= -10) && (Pri <= 10)) && std::move_constructible<T>
    struct simple_worker
    {
        std::atomic<bool> accepting_items {true};
        std::atomic<bool> shutdown_initiated {false};
        std::once_flag    shutdown_invoked;

        static constexpr std::chrono::milliseconds DEFAULT_WAIT_FOR_NEXT_ITEM_MS {1500};
        static constexpr std::chrono::milliseconds DEFAULT_SHUTDOWN_DRAIN_MS {1000};
 
    public:
        simple_worker(const simple_worker&) = delete;

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

        ~simple_worker()
        {
#if defined(DEBUG) || defined(_DEBUG)
            std::cerr << std::format("{} - Waiting for queue to be empty: {}\n", __func__, items.toJson().dump(2));
#endif
            // Performs a graceful shutdown (drains and kills the threads.)
            shutdown();
        }
 
        bool shutdown(std::chrono::milliseconds timeout = DEFAULT_SHUTDOWN_DRAIN_MS)
        {
            bool shutdown_status {false};
 
            std::call_once(
                    shutdown_invoked,
                    [&](bool& status, std::chrono::milliseconds& t) {
                        accepting_items.store(false, std::memory_order_release);
#if defined(DEBUG)
                        std::cerr << std::format("worker shutdown started inside call_once.. asking for waitUntilEmpty...for {}ms\n", t.count());
#endif
 
                        // Drain existing items and wait for the queue to be empty.
                        // Add a total deadline with buffer of 500ms extra..
                        auto deadline  = std::chrono::steady_clock::now() + t + std::chrono::milliseconds(500);
                        auto isDrained = items.waitUntilEmpty(t);
 
#if defined(DEBUG)
                        std::cerr << std::format("worker shutdown possible; isDrained: {}. size:{}\n", isDrained, items.size());
#endif
 
                        // Notify the processor to shutdown (we should have no outstanding items.)
                        processor.request_stop();
#if defined(DEBUG)
                        std::cerr << std::format("worker shutdown started inside call_once\n");
#endif
 
                        if (processor.joinable()) {
                            processor.join();
                            status = isDrained;
#if defined(DEBUG)
                            std::cerr << std::format("worker shutdown ok; isDrained: {}. size:{}\n", isDrained, items.size());
#endif
                        }
#if defined(DEBUG)
                        else {
                            std::cerr << std::format("worker shutdown failed; isDrained: {}. size:{}\n", isDrained, items.size());
                        }
 
                        std::cerr << "WARNING: Graceful shutdown timeout exceeded\n";
#endif
 
                        status = isDrained; // Timeout occurred
                    },
                    shutdown_status,
                    timeout);
            return shutdown_status;
        }

        simple_worker(simple_worker&&) = delete;

        simple_worker& operator=(simple_worker&&) = delete;

        simple_worker(std::function<void(T&&)> c)
            : callback(c)
        {
        }
 

        void queue(T&& item) noexcept(false)
        {
            if (!accepting_items.load(std::memory_order_acquire)) {
                throw std::runtime_error("Worker is shutting down, cannot queue new items");
            }
 
            items.emplace(std::move(item));
            queueCounter.fetch_add(1, std::memory_order_release);
        }
 
#if defined(NLOHMANN_JSON_VERSION_MAJOR)
        auto toJson() const -> nlohmann::json
        {
            auto itemsSize        = items.size();
            auto itemsQueued      = items.addCounter();
            auto itemsPopped      = items.removeCounter();
            auto itemsOutstanding = itemsQueued - itemsPopped;
 
            return {{"_typver", "siddiqsoft.asynchrony-lib.simple_worker/0.10"},
                    {"itemsSize", itemsSize},
                    {"queueCounter", queueCounter.load(std::memory_order_acquire)},
                    {"itemsQueued", itemsQueued},
                    {"itemsPopped", itemsPopped},
                    {"itemsOutstanding", itemsOutstanding},
                    {"threadPriority", Pri},
                    {"outstandingCallback", outstandingCallback.load(std::memory_order_acquire)},
                    {"waitInterval", DEFAULT_WAIT_FOR_NEXT_ITEM_MS.count()}};
        }
#endif
 
    private:
        std::once_flag flag_forceCleanupTerminate {};

        std::atomic_uint outstandingCallback {0};

        std::atomic_uint64_t queueCounter {0};

        siddiqsoft::WaitableQueue<T> items {};

        std::function<void(T&&)> callback;

        std::jthread processor {[&](std::stop_token st) {
#if defined(WIN64) || defined(_WIN64) || defined(WIN32) || defined(_WIN32)
            // Set the thread priority if possible
            if constexpr (Pri != 0) SetThreadPriority(GetCurrentThread(), Pri);
#endif
 
            while (!st.stop_requested()) {
                try {
                    // The getNextItem performs the wait on the signal and if it expires, returns empty.
                    // If there is an item, it will get that item (minimizing move) and performs the pop
                    // and returns the item so we can invoke the callback outside the lock.
                    // We must ensure that the callback is nonempty!
                    if (auto item = items.tryWaitItem(DEFAULT_WAIT_FOR_NEXT_ITEM_MS); item && !st.stop_requested() && callback) {
                        // Delegate to the callback outside the lock
                        try {
                            // We get an optional<> and thus the use of the * to get the value if present..
                            callback(std::move(*item));
                        }
                        catch (const std::exception& ex) {
                            // We swallow exceptions from the callback to avoid thread termination and log it if needed.
                            std::cerr << std::format("Ignoring Exception in simple_worker callback: {} - inner\n", ex.what());
                        }
                    }
                }
                catch (const std::exception& ex) {
                    // We swallow exceptions from the callback to avoid thread termination and log it if needed.
                    std::cerr << std::format("Ignoring Exception in simple_worker callback: {} - outer\n", ex.what());
                }
            } // while ..continue until we're asked to stop
#if defined(DEBUG)
            std::cerr << std::format("WARNING: Abandon {} items processing due to stop request!\n", items.size());
#endif
        }};
    };
 
#if defined(NLOHMANN_JSON_VERSION_MAJOR)
    template <typename T, int Pri = 0>
    static void to_json(nlohmann::json& dest, const siddiqsoft::simple_worker<T, Pri>& src)
    {
        dest = src.toJson();
    }
#endif
 
} // namespace siddiqsoft
#endif // !SIMPLE_WORKER_HPP