beedb/include/concurrency/timestamp.h

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/*------------------------------------------------------------------------------*
* Architecture & Implementation of DBMS *
*------------------------------------------------------------------------------*
* Copyright 2022 Databases and Information Systems Group TU Dortmund *
* Visit us at *
* http://dbis.cs.tu-dortmund.de/cms/en/home/ *
* *
* 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. *
* *
* Authors: *
* Maximilian Berens <maximilian.berens@tu-dortmund.de> *
* Roland Kühn <roland.kuehn@cs.tu-dortmund.de> *
* Jan Mühlig <jan.muehlig@tu-dortmund.de> *
*------------------------------------------------------------------------------*
*/
#pragma once
#include <cstdint>
namespace beedb::concurrency
{
/**
* Represents a transaction timestamp, e.g., a begin or end timestamp
* of a record or begin or commit time of a transaction.
* The timestamp contains the "real" time (that is a global counter incremented
* for each new transaction) and a flag that indices the commit-state of the timestamp.
* The flag may be 1 for committed and else 0.
*
* The time "0" in combination with the set committed flag indicates "infinity".
*/
class alignas(64) timestamp
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{
public:
using timestamp_t = std::uint64_t;
static auto make_infinity()
{
return timestamp{};
}
timestamp(const timestamp_t t, bool is_committed) : _timestamp_and_committed_flag((t << 1u) | is_committed)
{
}
timestamp &operator=(const timestamp &) = default;
~timestamp() = default;
/**
* @return True, if the transaction of the timestamp was committed.
*/
[[nodiscard]] bool is_committed() const
{
return _timestamp_and_committed_flag & 1u;
}
/**
* @return The "real" time without "committed" flag.
*/
[[nodiscard]] timestamp_t time() const
{
return _timestamp_and_committed_flag >> 1u;
}
/**
* @return True, when this timestamp is "never ending".
*/
[[nodiscard]] bool is_infinity() const
{
return _timestamp_and_committed_flag == 1u;
}
bool operator==(const timestamp other) const
{
return other._timestamp_and_committed_flag == _timestamp_and_committed_flag;
}
bool operator!=(const timestamp other) const
{
return other._timestamp_and_committed_flag != _timestamp_and_committed_flag;
}
bool operator<(const timestamp other) const
{
return time() < other.time();
}
bool operator<=(const timestamp other) const
{
return time() <= other.time();
}
bool operator>(const timestamp other) const
{
return time() > other.time();
}
bool operator>=(const timestamp other) const
{
return time() >= other.time();
}
private:
timestamp() = default;
// Time and committed flag (last bit).
timestamp_t _timestamp_and_committed_flag = 1u;
};
} // namespace beedb::concurrency