transmission/libtransmission/history.h

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// This file Copyright 2010-2022 Mnemosyne LLC.
// It may be used under GPLv2 (SPDX: GPL-2.0), GPLv3 (SPDX: GPL-3.0),
// or any future license endorsed by Mnemosyne LLC.
// License text can be found in the licenses/ folder.
#pragma once
#ifndef __TRANSMISSION__
#error only libtransmission should #include this header.
#endif
#include <array>
#include <cstddef> // size_t
#include <ctime> // time_t
#include <numeric> // std::accumulate
/**
* A short-term memory object that remembers how many times something
* happened over the last N seconds. tr_peer uses it to count how many
* bytes transferred to estimate the speed over the last N seconds.
*/
class tr_recentHistory
{
public:
/**
* @brief add a counter to the recent history object.
* @param when the current time in sec, such as from tr_time()
* @param n how many items to add to the history's counter
*/
void add(time_t now, size_t n)
{
if (slices[newest].time != now)
{
newest = (newest + 1) % TR_RECENT_HISTORY_PERIOD_SEC;
slices[newest].time = now;
}
slices[newest].n += n;
}
/**
* @brief count how many events have occurred in the last N seconds.
* @param when the current time in sec, such as from tr_time()
* @param seconds how many seconds to count back through.
*/
size_t count(time_t now, unsigned int age_sec) const
{
time_t const oldest = now - age_sec;
return std::accumulate(
std::begin(slices),
std::end(slices),
size_t{ 0 },
[&oldest](size_t sum, auto const& slice) { return slice.time >= oldest ? sum + slice.n : sum; });
}
private:
inline auto static constexpr TR_RECENT_HISTORY_PERIOD_SEC = size_t{ 60 };
int newest = 0;
struct slice_t
{
size_t n = 0;
time_t time = 0;
};
std::array<slice_t, TR_RECENT_HISTORY_PERIOD_SEC> slices = {};
};