transmission/libtransmission/bandwidth.h

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// This file Copyright © Mnemosyne LLC.
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// It may be used under GPLv2 (SPDX: GPL-2.0-only), GPLv3 (SPDX: GPL-3.0-only),
// 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 <cstdint> // uint64_t
#include <memory>
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#include <utility> // for std::move()
#include <vector>
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#include "libtransmission/transmission.h"
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#include "libtransmission/tr-assert.h"
class tr_peerIo;
/**
* @addtogroup networked_io Networked IO
* @{
*/
struct tr_bandwidth_limits
{
tr_kilobytes_per_second_t up_limit_KBps = 0U;
tr_kilobytes_per_second_t down_limit_KBps = 0U;
bool up_limited = false;
bool down_limited = false;
};
/**
* `tr_bandwidth` is an object for measuring and constraining bandwidth speeds.
*
* `tr_bandwidth` objects can be "stacked" so that a peer can be made to obey
* multiple constraints (for example, obeying the global speed limit and a
* per-torrent speed limit).
*
* HIERARCHY
*
* Transmission's bandwidth hierarchy is a tree.
* At the top is the global bandwidth object owned by `tr_session`.
* Its children are per-torrent bandwidth objects owned by `tr_torrent`.
* Underneath those are per-peer bandwidth objects owned by `tr_peer`.
*
* `tr_session` also owns a `tr_handshake`'s bandwidths, so that the handshake
* I/O can be counted in the global raw totals. When the handshake is done,
* the bandwidth's ownership passes to a `tr_peer`.
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*
* MEASURING
*
* When you ask a bandwidth object for its speed, it gives the speed of the
* subtree underneath it as well. So you can get Transmission's overall
* speed by querying `tr_session`'s bandwidth, per-torrent speeds by asking
* `tr_torrent`'s bandwidth, and per-peer speeds by asking `tr_peer`'s bandwidth.
*
* CONSTRAINING
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*
* Call `tr_bandwidth::allocate()` periodically. `tr_bandwidth` knows its current
* speed and will decide how many bytes to make available over the
* user-specified period to reach the user-specified desired speed.
* If appropriate, it notifies its peer-ios that new bandwidth is available.
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*
* `tr_bandwidth::allocate()` operates on the `tr_bandwidth` subtree, so usually
* you'll only need to invoke it for the top-level `tr_session` bandwidth.
*
* The peer-ios all have a pointer to their associated `tr_bandwidth` object,
* and call `tr_bandwidth::clamp()` before performing I/O to see how much
* bandwidth they can safely use.
*/
struct tr_bandwidth
{
private:
static constexpr size_t HistoryMSec = 2000U;
static constexpr size_t GranularityMSec = 250U;
static constexpr size_t HistorySize = HistoryMSec / GranularityMSec;
public:
explicit tr_bandwidth(tr_bandwidth* new_parent);
tr_bandwidth()
: tr_bandwidth(nullptr)
{
}
~tr_bandwidth() noexcept
{
deparent();
}
tr_bandwidth& operator=(tr_bandwidth&&) = delete;
tr_bandwidth& operator=(tr_bandwidth) = delete;
tr_bandwidth(tr_bandwidth&&) = delete;
tr_bandwidth(tr_bandwidth&) = delete;
/**
* @brief Sets the peer. nullptr is allowed.
*/
void set_peer(std::weak_ptr<tr_peerIo> peer) noexcept
{
this->peer_ = std::move(peer);
}
/**
* @brief Notify the bandwidth object that some of its allocated bandwidth has been consumed.
* This is is usually invoked by the peer-io after a read or write.
*/
void notify_bandwidth_consumed(tr_direction dir, size_t byte_count, bool is_piece_data, uint64_t now);
/**
* @brief allocate the next `period_msec`'s worth of bandwidth for the peer-ios to consume
*/
void allocate(uint64_t period_msec);
void set_parent(tr_bandwidth* new_parent);
[[nodiscard]] constexpr tr_priority_t get_priority() const noexcept
{
return this->priority_;
}
constexpr void set_priority(tr_priority_t prio) noexcept
{
this->priority_ = prio;
}
/**
* @brief clamps `byte_count` down to a number that this bandwidth will allow to be consumed
*/
[[nodiscard]] size_t clamp(tr_direction dir, size_t byte_count) const noexcept;
/** @brief Get the raw total of bytes read or sent by this bandwidth subtree. */
[[nodiscard]] auto get_raw_speed_bytes_per_second(uint64_t const now, tr_direction const dir) const
{
TR_ASSERT(tr_isDirection(dir));
return get_speed_bytes_per_second(this->band_[dir].raw_, HistoryMSec, now);
}
/** @brief Get the number of piece data bytes read or sent by this bandwidth subtree. */
[[nodiscard]] auto get_piece_speed_bytes_per_second(uint64_t const now, tr_direction const dir) const
{
TR_ASSERT(tr_isDirection(dir));
return get_speed_bytes_per_second(this->band_[dir].piece_, HistoryMSec, now);
}
/**
* @brief Set the desired speed for this bandwidth subtree.
* @see `tr_bandwidth::allocate`
* @see `tr_bandwidth::getDesiredSpeed`
*/
constexpr bool set_desired_speed_bytes_per_second(tr_direction dir, tr_bytes_per_second_t desired_speed)
{
auto& value = this->band_[dir].desired_speed_bps_;
bool const did_change = desired_speed != value;
value = desired_speed;
return did_change;
}
/**
* @brief Get the desired speed for the bandwidth subtree.
* @see `tr_bandwidth::setDesiredSpeed`
*/
[[nodiscard]] constexpr auto get_desired_speed_bytes_per_second(tr_direction dir) const
{
return this->band_[dir].desired_speed_bps_;
}
[[nodiscard]] bool is_maxed_out(tr_direction dir, uint64_t now_msec) const noexcept
{
if (!is_limited(dir))
{
return false;
}
auto const got = get_piece_speed_bytes_per_second(now_msec, dir);
auto const want = get_desired_speed_bytes_per_second(dir);
return got >= want;
}
/**
* @brief Set whether or not this bandwidth should throttle its peer-io's speeds
*/
constexpr bool set_limited(tr_direction dir, bool is_limited)
{
bool& value = this->band_[dir].is_limited_;
bool const did_change = is_limited != value;
value = is_limited;
return did_change;
}
/**
* @return nonzero if this bandwidth throttles its peer-ios speeds
*/
[[nodiscard]] constexpr bool is_limited(tr_direction dir) const noexcept
{
return this->band_[dir].is_limited_;
}
/**
* Almost all the time we do want to honor a parents' bandwidth cap, so that
* (for example) a peer is constrained by a per-torrent cap and the global cap.
* But when we set a torrent's speed mode to `TR_SPEEDLIMIT_UNLIMITED`, then
* in that particular case we want to ignore the global speed limit...
*/
constexpr bool honor_parent_limits(tr_direction direction, bool is_enabled)
{
bool& value = this->band_[direction].honor_parent_limits_;
bool const did_change = is_enabled != value;
value = is_enabled;
return did_change;
}
[[nodiscard]] constexpr bool are_parent_limits_honored(tr_direction direction) const
{
TR_ASSERT(tr_isDirection(direction));
return this->band_[direction].honor_parent_limits_;
}
[[nodiscard]] tr_bandwidth_limits get_limits() const;
void set_limits(tr_bandwidth_limits const& limits);
private:
struct RateControl
{
std::array<uint64_t, HistorySize> date_;
std::array<size_t, HistorySize> size_;
uint64_t cache_time_;
tr_bytes_per_second_t cache_val_;
int newest_;
};
struct Band
{
RateControl raw_;
RateControl piece_;
size_t bytes_left_;
tr_bytes_per_second_t desired_speed_bps_;
bool is_limited_ = false;
bool honor_parent_limits_ = true;
};
static tr_bytes_per_second_t get_speed_bytes_per_second(RateControl& r, unsigned int interval_msec, uint64_t now);
[[nodiscard]] constexpr auto* parent() noexcept
{
return parent_;
}
void deparent() noexcept;
static void notify_bandwidth_consumed_bytes(uint64_t now, RateControl& r, size_t size);
static void phase_one(std::vector<tr_peerIo*>& peers, tr_direction dir);
void allocate_bandwidth(
tr_priority_t parent_priority,
uint64_t period_msec,
std::vector<std::shared_ptr<tr_peerIo>>& peer_pool);
mutable std::array<Band, 2> band_ = {};
std::vector<tr_bandwidth*> children_;
tr_bandwidth* parent_ = nullptr;
std::weak_ptr<tr_peerIo> peer_;
tr_priority_t priority_ = 0;
};
/* @} */