circular_q.h
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// Copyright(c) 2015-present, Gabi Melman & spdlog contributors.
// Distributed under the MIT License (http://opensource.org/licenses/MIT)
// circular q view of std::vector.
#pragma once
#include <vector>
#include <cassert>
namespace spdlog {
namespace details {
template<typename T>
class circular_q
{
size_t max_items_ = 0;
typename std::vector<T>::size_type head_ = 0;
typename std::vector<T>::size_type tail_ = 0;
size_t overrun_counter_ = 0;
std::vector<T> v_;
public:
using value_type = T;
// empty ctor - create a disabled queue with no elements allocated at all
circular_q() = default;
explicit circular_q(size_t max_items)
: max_items_(max_items + 1) // one item is reserved as marker for full q
, v_(max_items_)
{}
circular_q(const circular_q &) = default;
circular_q &operator=(const circular_q &) = default;
// move cannot be default,
// since we need to reset head_, tail_, etc to zero in the moved object
circular_q(circular_q &&other) SPDLOG_NOEXCEPT
{
copy_moveable(std::move(other));
}
circular_q &operator=(circular_q &&other) SPDLOG_NOEXCEPT
{
copy_moveable(std::move(other));
return *this;
}
// push back, overrun (oldest) item if no room left
void push_back(T &&item)
{
if (max_items_ > 0)
{
v_[tail_] = std::move(item);
tail_ = (tail_ + 1) % max_items_;
if (tail_ == head_) // overrun last item if full
{
head_ = (head_ + 1) % max_items_;
++overrun_counter_;
}
}
}
// Return reference to the front item.
// If there are no elements in the container, the behavior is undefined.
const T &front() const
{
return v_[head_];
}
T &front()
{
return v_[head_];
}
// Return number of elements actually stored
size_t size() const
{
if (tail_ >= head_)
{
return tail_ - head_;
}
else
{
return max_items_ - (head_ - tail_);
}
}
// Return const reference to item by index.
// If index is out of range 0…size()-1, the behavior is undefined.
const T &at(size_t i) const
{
assert(i < size());
return v_[(head_ + i) % max_items_];
}
// Pop item from front.
// If there are no elements in the container, the behavior is undefined.
void pop_front()
{
head_ = (head_ + 1) % max_items_;
}
bool empty() const
{
return tail_ == head_;
}
bool full() const
{
// head is ahead of the tail by 1
if (max_items_ > 0)
{
return ((tail_ + 1) % max_items_) == head_;
}
return false;
}
size_t overrun_counter() const
{
return overrun_counter_;
}
private:
// copy from other&& and reset it to disabled state
void copy_moveable(circular_q &&other) SPDLOG_NOEXCEPT
{
max_items_ = other.max_items_;
head_ = other.head_;
tail_ = other.tail_;
overrun_counter_ = other.overrun_counter_;
v_ = std::move(other.v_);
// put &&other in disabled, but valid state
other.max_items_ = 0;
other.head_ = other.tail_ = 0;
other.overrun_counter_ = 0;
}
};
} // namespace details
} // namespace spdlog