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// Copyright Vespa.ai. Licensed under the terms of the Apache 2.0 license. See LICENSE in the project root.
#pragma once
#include <cstdint>
#include <atomic>
namespace vespalib {
/**
* @brief A GenCnt object wraps an integer generation counter.
*
* The value 0 is special, as when the internal counter wraps around
* it will skip this value. This gives 0 a special meaning as the
* first generation, and it will be different from all later
* generations, even when the counter wraps around.
**/
class GenCnt
{
private:
std::atomic<uint32_t> _val;
public:
/**
* @brief Create a generation counter with value 0
**/
GenCnt() noexcept : _val(0) {}
/**
* @brief Create a generation counter with the given value
*
* @param val initial value
**/
GenCnt(uint32_t val) noexcept : _val(val) {}
GenCnt(const GenCnt &rhs) noexcept : _val(rhs.getAsInt()) {}
/**
* @brief empty destructor
**/
~GenCnt() = default;
/**
* @brief Increase the generation count held by this object
*
* @return this object, for chaining
* @param n how much to increment the generation counter
**/
GenCnt &add(uint32_t n = 1);
/**
* @brief Check if this generation counter is inside the given
* range
*
* @return true if this generation is inside the range
* @param a the first generation in the range (inclusive)
* @param b the last generation in the range (inclusive)
**/
bool inRangeInclusive(GenCnt a, GenCnt b) const;
/**
* @brief Get the distance in generations between this object and
* the one given as 'other'.
*
* Note that this object is assumed to occur before 'other'.
* @return distance between this and other
* @param other other object occurring after this one
**/
uint32_t distance(const GenCnt &other) const;
/**
* @brief Check if this GenCnt is equal to another GenCnt
*
* @return true if <i>this</i> is equal to <i>rhs</i>
* @param rhs the right hand side in the comparison
**/
bool operator==(const GenCnt &rhs) const { return rhs._val == _val; }
/**
* @brief Check if this GenCnt is not equal to another GenCnt
*
* @return true if <i>this</i> is not equal to <i>rhs</i>
* @param rhs the right hand side in the comparison
**/
bool operator!=(const GenCnt &rhs) const { return rhs._val != _val; }
/**
* @brief Assignment operator
*
* @return this object
* @param src the object we want to copy
**/
GenCnt &operator=(const GenCnt &src);
/**
* @brief Get the generation counter as an integer
*
* @return generation counter
**/
uint32_t getAsInt() const { return _val.load(std::memory_order_relaxed); }
/**
* @brief Set the generation counter from an integer
*
* @param val generation counter
**/
void setFromInt(uint32_t val) { _val = val; }
/**
* @brief Reset the value of this reference counter to 0
**/
void reset() { _val = 0; }
};
} // namespace vespalib
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