pool.h

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#ifndef HEDGEHOG_POOL_H_
#define HEDGEHOG_POOL_H_
 
#pragma once
 
#include <deque>
#include <memory>
#include <sstream>
#include <condition_variable>
 
namespace hh {
namespace tool {
 
template<class T>
class Pool {
 private:
  size_t const capacity_ = 1; 
  std::deque<std::shared_ptr<T>> queue_ = {}; 
  std::mutex mutex_ = {}; 
  std::unique_ptr<std::condition_variable>
      conditionVariable_ = std::make_unique<std::condition_variable>(); 
 public:
  explicit Pool(size_t const &capacity) : capacity_(capacity == 0 ? 1 : capacity) {
    queue_ = std::deque<std::shared_ptr<T >>(capacity_);
  }
 
  typename std::deque<std::shared_ptr<T>>::iterator begin() { return this->queue_.begin(); }
 
  typename std::deque<std::shared_ptr<T>>::iterator end() { return this->queue_.end(); }
 
  size_t size() {
    mutex_.lock();
    auto s = queue_.size();
    mutex_.unlock();
    return s;
  }
 
  bool empty() {
    mutex_.lock();
    auto e = queue_.empty();
    mutex_.unlock();
    return e;
  }
 
  [[nodiscard]] size_t capacity() const { return capacity_; }
 
  void push_back(std::shared_ptr<T> const &data) {
    mutex_.lock();
    this->queue_.push_back(data);
 
    if (this->queue_.size() > capacity_) {
      std::ostringstream oss;
      oss << "The queue is overflowing, the same data " << data
          << " has been returned to the memory manager too many times: " << __FUNCTION__;
      throw (std::runtime_error(oss.str()));
    }
    mutex_.unlock();
    conditionVariable_->notify_one();
  }
 
  std::shared_ptr<T> pop_front() {
    std::unique_lock<std::mutex> lock(mutex_);
    std::shared_ptr<T> ret = nullptr;
    conditionVariable_->wait(lock, [this]() { return !queue_.empty(); });
    ret = queue_.front();
    queue_.pop_front();
    return ret;
  }
};
}
}
#endif //HEDGEHOG_POOL_H_