synchronized_queue.h

#ifndef SYNCHRONIZED_QUEUE_H
#define SYNCHRONIZED_QUEUE_H

#include <condition_variable>
#include <cstddef>
#include <cstdlib>
#include <deque>
#include <memory>
#include <mutex>
#include <optional>
#include <thread>
#include <utility>

namespace ds {

template <typename Data>
  requires(std::copyable<Data> || std::movable<Data>)
class SynchronizedQueue {
  std::deque<Data> data;
  mutable std::mutex lock;
  std::condition_variable conditional;

  auto pop_and_return() {
    auto retval = std::move(data.front());
    data.pop_front();
    return retval;
  }

 public:
  std::optional<Data> try_pop() {
    std::lock_guard<std::mutex> guard(lock);
    if (data.empty())
      return {};

    return pop_and_return();
  }

  Data wait_and_pop() {
    std::unique_lock<std::mutex> guard(lock);
    conditional.wait(guard, [this]() { return !data.empty(); });

    return pop_and_return();
  }

  void push(Data val) {
    std::lock_guard<std::mutex> guard(lock);
    data.emplace_back(val);
    conditional.notify_one();
  }

  size_t was_size() const {
    std::lock_guard<std::mutex> guard(lock);
    return data.size();
  }

  bool was_empty() const {
    std::lock_guard<std::mutex> guard(lock);
    return data.empty();
  }
};

}  // namespace ds

#endif  // SYNCHRONIZED_QUEUE_H