transmission/libtransmission/bandwidth.h

/*
 * This file Copyright (C) Mnemosyne LLC
 *
 * This file is licensed by the GPL version 2. Works owned by the
 * Transmission project are granted a special exemption to clause 2 (b)
 * so that the bulk of its code can remain under the MIT license.
 * This exemption does not extend to derived works not owned by
 * the Transmission project.
 *
 * $Id$
 */

#ifndef __TRANSMISSION__
#error only libtransmission should #include this header.
#endif

#ifndef TR_BANDWIDTH_H
#define TR_BANDWIDTH_H

#include <assert.h>

#include "transmission.h"
#include "ptrarray.h"
#include "utils.h" /* tr_new (), tr_free () */

struct tr_peerIo;

/**
 * @addtogroup networked_io Networked IO
 * @{
 */

/* these are PRIVATE IMPLEMENTATION details that should not be touched.
 * it's included in the header for inlining and composition. */
enum
{
  HISTORY_MSEC = 2000u,
  INTERVAL_MSEC = HISTORY_MSEC,
  GRANULARITY_MSEC = 200,
  HISTORY_SIZE = (INTERVAL_MSEC / GRANULARITY_MSEC),
  BANDWIDTH_MAGIC_NUMBER = 43143
};

/* these are PRIVATE IMPLEMENTATION details that should not be touched.
 * it's included in the header for inlining and composition. */
struct bratecontrol
{
  int newest;
  struct { uint64_t date, size; } transfers[HISTORY_SIZE];
  uint64_t cache_time;
  unsigned int cache_val;
};

/* these are PRIVATE IMPLEMENTATION details that should not be touched.
 * it's included in the header for inlining and composition. */
struct tr_band
{
  bool isLimited;
  bool honorParentLimits;
  unsigned int bytesLeft;
  unsigned int desiredSpeed_Bps;
  struct bratecontrol raw;
  struct bratecontrol piece;
};

/**
 * Bandwidth is an object for measuring and constraining bandwidth speeds.
 *
 * 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.
 *
 * 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 quering tr_session's bandwidth, per-torrent speeds by asking
 *   tr_torrent's bandwidth, and per-peer speeds by asking tr_peer's bandwidth.
 *
 * CONSTRAINING
 *
 *   Call tr_bandwidthAllocate () 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.
 *
 *   tr_bandwidthAllocate () 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_bandwidthClamp () before performing I/O to see how much
 *   bandwidth they can safely use.
 */
typedef struct tr_bandwidth
{
  /* these are PRIVATE IMPLEMENTATION details that should not be touched.
   * it's included in the header for inlining and composition. */

  struct tr_band band[2];
  struct tr_bandwidth * parent;
  tr_priority_t priority;
  int magicNumber;
  unsigned int uniqueKey;
  tr_session * session;
  tr_ptrArray children; /* struct tr_bandwidth */
  struct tr_peerIo * peer;
}
tr_bandwidth;


/**
***
**/

void tr_bandwidthConstruct (tr_bandwidth * bandwidth,
                            tr_session   * session,
                            tr_bandwidth * parent);

void tr_bandwidthDestruct (tr_bandwidth * bandwidth);

/** @brief test to see if the pointer refers to a live bandwidth object */
static inline bool
tr_isBandwidth (const tr_bandwidth  * b)
{
  return (b != NULL) && (b->magicNumber == BANDWIDTH_MAGIC_NUMBER);
}

/******
*******
******/

/**
 * @brief Set the desired speed for this bandwidth subtree.
 * @see tr_bandwidthAllocate
 * @see tr_bandwidthGetDesiredSpeed
 */
static inline bool
tr_bandwidthSetDesiredSpeed_Bps (tr_bandwidth  * bandwidth,
                                 tr_direction    dir,
                                 unsigned int    desiredSpeed)
{
  unsigned int * value = &bandwidth->band[dir].desiredSpeed_Bps;
  const bool didChange = desiredSpeed != *value;
  *value = desiredSpeed;
  return didChange;
}

/**
 * @brief Get the desired speed for the bandwidth subtree.
 * @see tr_bandwidthSetDesiredSpeed
 */
static inline double
tr_bandwidthGetDesiredSpeed_Bps (const tr_bandwidth  * bandwidth, tr_direction dir)
{
  return bandwidth->band[dir].desiredSpeed_Bps;
}

/**
 * @brief Set whether or not this bandwidth should throttle its peer-io's speeds
 */
static inline bool
tr_bandwidthSetLimited (tr_bandwidth  * bandwidth,
                        tr_direction    dir,
                        bool            isLimited)
{
  bool * value = &bandwidth->band[dir].isLimited;
  const bool didChange = isLimited != *value;
  *value = isLimited;
  return didChange;
}

/**
 * @return nonzero if this bandwidth throttles its peer-ios speeds
 */
static inline bool
tr_bandwidthIsLimited (const tr_bandwidth  * bandwidth,
                       tr_direction          dir)
{
  return bandwidth->band[dir].isLimited;
}

/**
 * @brief allocate the next period_msec's worth of bandwidth for the peer-ios to consume
 */
void tr_bandwidthAllocate (tr_bandwidth  * bandwidth,
                           tr_direction    direction,
                           unsigned int    period_msec);

/**
 * @brief clamps byteCount down to a number that this bandwidth will allow to be consumed
 */
unsigned int tr_bandwidthClamp (const tr_bandwidth  * bandwidth,
                                tr_direction          direction,
                                unsigned int          byteCount);

/******
*******
******/

/** @brief Get the raw total of bytes read or sent by this bandwidth subtree. */
unsigned int tr_bandwidthGetRawSpeed_Bps (const tr_bandwidth  * bandwidth,
                                          const uint64_t        now,
                                          const tr_direction    direction);

/** @brief Get the number of piece data bytes read or sent by this bandwidth subtree. */
unsigned int tr_bandwidthGetPieceSpeed_Bps (const tr_bandwidth  * bandwidth,
                                            const uint64_t        now,
                                            const tr_direction    direction);

/**
 * @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 tr_bandwidthUsed (tr_bandwidth  * bandwidth,
                       tr_direction    direction,
                       size_t          byteCount,
                       bool            isPieceData,
                       uint64_t        now);

/******
*******
******/

void tr_bandwidthSetParent (tr_bandwidth  * bandwidth,
                            tr_bandwidth  * parent);

/**
 * 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...
 */
static inline bool
tr_bandwidthHonorParentLimits (tr_bandwidth   * bandwidth,
                               tr_direction     direction,
                               bool             isEnabled)
{
  bool * value = &bandwidth->band[direction].honorParentLimits;
  const bool didChange = isEnabled != *value;
  *value = isEnabled;
  return didChange;
}

static inline bool
tr_bandwidthAreParentLimitsHonored (const tr_bandwidth  * bandwidth,
                                    tr_direction          direction)
{
  assert (tr_isBandwidth (bandwidth));
  assert (tr_isDirection (direction));

  return bandwidth->band[direction].honorParentLimits;
}

/******
*******
******/

void tr_bandwidthSetPeer (tr_bandwidth      * bandwidth,
                          struct tr_peerIo  * peerIo);

/* @} */
#endif