log.hpp

/*
Copyright (c) 2015 Erik Rigtorp <erik@rigtorp.se>

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.
 */

#pragma once

#include <atomic>
#include <chrono>
#include <fstream>
#include <iostream>
#include <memory>
#include <mutex>
#include <tuple>
#include <type_traits>
#include <utility>
#include <vector>

class Formatter {
public:
  static void format(std::ostream &o) { o << "\n"; }

  template <typename T, typename... Args>
  static void format(std::ostream &o, T &&t, Args &&... args) {
    o << t << " ";
    format(o, std::forward<Args>(args)...);
  }
};

class Message {
public:
  template <typename... Args> Message(Args &&... args) {
    fp = pack(&data, std::forward<Args>(args)...);
  }

  ~Message() {
    // make sure destructors are called
    fp(nullptr, &data);
  }

  void Format(std::ostream &o) { fp(&o, &data); }

private:
  Message(Message &other) = delete;
  Message &operator=(const Message &) = delete;
  Message(Message &&other) = delete;
  Message &operator=(Message &&) = delete;

  template <typename Tup, std::size_t... index>
  static void call_format_helper(std::ostream &o, Tup &&args,
                                 std::index_sequence<index...>) {
    Formatter::format(o, std::get<index>(std::forward<Tup>(args))...);
  }

  template <typename... Args>
  static void call_format(std::ostream *o, void *p) {
    typedef std::tuple<Args...> Tup;
    Tup &args = *reinterpret_cast<Tup *>(p);
    if (o) {
      call_format_helper(*o, args, std::index_sequence_for<Args...>{});
    } else {
      // important to call destructor for complex types
      args.~Tup();
    }
  }

  template <typename T, typename... Args>
  static decltype(auto) pack(T *p, Args &&... args) {
    typedef std::tuple<typename std::decay<Args>::type...> Tup;
    static_assert(alignof(Tup) <= alignof(T), "invalid alignment");
    static_assert(sizeof(Tup) <= sizeof(T), "storage too small");
    new (p) Tup(std::forward<Args>(args)...);
    return &call_format<typename std::decay<Args>::type...>;
  }

  using FormatFun = void (*)(std::ostream *, void *);
  using Storage = typename std::aligned_storage<56, 8>::type;

  FormatFun fp;
  Storage data;
};

static_assert(sizeof(Message) == 64, "message not a cache line in size");

template <typename T> class Queue {
  // Ringbuffer, fixed size single producer single consumer lock-free queue
public:
  Queue(const size_t size)
      : size_(size), buffer_(static_cast<T *>(std::malloc(sizeof(T) * size))),
        head_(0), tail_(0) {
    if (!buffer_) {
      throw std::bad_alloc();
    }
  }

  ~Queue() {
    while (front()) {
      pop();
    }
    std::free(buffer_);
  }

  template <typename... Args> void emplace(Args &&... args) {
    auto const head = head_.load(std::memory_order_relaxed);
    auto const next_head = (head + 1) % size_;
    while (next_head == tail_.load(std::memory_order_acquire))
      ;
    new (&buffer_[head]) T(std::forward<Args>(args)...);
    head_.store(next_head, std::memory_order_release);
  }

  T *front() {
    auto tail = tail_.load(std::memory_order_relaxed);
    if (head_.load(std::memory_order_acquire) == tail) {
      return nullptr;
    }
    return &buffer_[tail];
  }

  void pop() {
    auto const tail = tail_.load(std::memory_order_relaxed);
    if (head_.load(std::memory_order_acquire) == tail) {
      return;
    }
    auto const next_tail = (tail + 1) % size_;
    buffer_[tail].~T();
    tail_.store(next_tail, std::memory_order_release);
  }

private:
  const size_t size_;
  T *const buffer_;
  std::atomic<size_t> head_, tail_;
};

class Logger {
public:
  template <typename... Args>
  static void Log(const char *fmt, Args &&... args) {
    queue().emplace(fmt, std::forward<Args>(args)...);
  }

  static void SetQueueSize(const size_t size) { instance().queue_size_ = size; }

  static void SetOutput(const std::string &fname) {
    Logger &logger = instance();
    std::lock_guard<std::mutex> lock(logger.mutex_);
    if (fname == "") {
      logger.ostream_.reset();
      logger.cout_ = false;
    } else if (fname == "-") {
      logger.ostream_.reset();
      logger.cout_ = true;
    } else {
      logger.ostream_ = std::make_unique<std::ofstream>(fname);
      logger.cout_ = false;
    }
  }

private:
  Logger() : active_(true), queues_size_(1), queue_size_(1024), cout_(true) {
    thread_ = std::thread([this] { Writer(); });
  }

  ~Logger() {
    active_ = false;
    if (thread_.joinable()) {
      thread_.join();
    }
  }

  Logger(Logger &other) = delete;
  Logger &operator=(const Logger &) = delete;
  Logger(Logger &&other) = delete;
  Logger &operator=(Logger &&) = delete;

  void Writer() {
    using namespace std::chrono_literals;
    while (active_ || queues_size_) {
      {
        std::lock_guard<std::mutex> lock(instance().mutex_);
        for (auto it = queues_.begin(); it != queues_.end();) {
          auto &q = *it;
          while (q->front()) {
            if (ostream_) {
              q->front()->Format(*ostream_);
            }
            if (cout_) {
              q->front()->Format(std::cout);
            }
            q->pop();
          }
          if (q.unique() && !q->front()) {
            it = queues_.erase(it);
          } else {
            ++it;
          }
        }
        queues_size_ = queues_.size();
      }
      // std::this_thread::sleep_for(100ms);
    }
  }

  static Logger &instance() {
    static Logger instance;
    return instance;
  }

  using QueueType = Queue<Message>;

  static QueueType &queue() {
    static thread_local std::shared_ptr<QueueType> queue;
    if (queue == nullptr) {
      queue = std::make_shared<QueueType>(instance().queue_size_);
      std::lock_guard<std::mutex> lock(instance().mutex_);
      instance().queues_.push_back(queue);
    }
    return *queue;
  }

  std::mutex mutex_;
  std::vector<std::shared_ptr<QueueType>> queues_;
  std::thread thread_;
  bool active_;
  size_t queues_size_;
  size_t queue_size_;
  bool cout_;
  std::unique_ptr<std::ostream> ostream_;
};