add_torrent_params()

add_torrent_params (storage_constructor_type sc = default_storage_constructor);

The constructor can be used to initialize the storage constructor, which determines the storage mechanism for the downloaded or seeding data for the torrent. For more information, see the storage field.

enum flags_t

Declared in "libtorrent/add_torrent_params.hpp"

version

filled in by the constructor and should be left untouched. It is used for forward binary compatibility.

ti

torrent_info object with the torrent to add. Unless the url or info_hash is set, this is required to be initiazlied.

trackers

If the torrent doesn't have a tracker, but relies on the DHT to find peers, the trackers can specify tracker URLs for the torrent.

url_seeds

url seeds to be added to the torrent (BEP 17).

dht_nodes name

a list of hostname and port pairs, representing DHT nodes to be added to the session (if DHT is enabled). The hostname may be an IP address.

save_path

the path where the torrent is or will be stored. Note that this may alos be stored in resume data. If you which the save path saved in the resume data to be used, you need to set the flag_use_resume_save_path flag.

resume_data

The optional parameter, resume_data can be given if up to date fast-resume data is available. The fast-resume data can be acquired from a running torrent by calling save_resume_data() on torrent_handle. See fast resume. The vector that is passed in will be swapped into the running torrent instance with std::vector::swap().

storage_mode

One of the values from storage_mode_t. For more information, see storage allocation.

storage

can be used to customize how the data is stored. The default storage will simply write the data to the files it belongs to, but it could be overridden to save everything to a single file at a specific location or encrypt the content on disk for instance. For more information about the storage_interface that needs to be implemented for a custom storage, see storage_interface.

userdata

The userdata parameter is optional and will be passed on to the extension constructor functions, if any (see add_extension()).

file_priorities

can be set to control the initial file priorities when adding a torrent. The semantics are the same as for torrent_handle::prioritize_files().

trackerid

the default tracker id to be used when announcing to trackers. By default this is empty, and no tracker ID is used, since this is an optional argument. If a tracker returns a tracker ID, that ID is used instead of this.

url

If you specify a url, the torrent will be set in downloading_metadata state until the .torrent file has been downloaded. If there's any error while downloading, the torrent will be stopped and the torrent error state (torrent_status::error) will indicate what went wrong. The url may refer to a magnet link or a regular http URL.

If it refers to an HTTP URL, the info-hash for the added torrent will not be the true info-hash of the .torrent. Instead a placeholder, unique, info-hash is used which is later updated once the .torrent file has been downloaded.

Once the info-hash change happens, a torrent_update_alert is posted.

uuid

if uuid is specified, it is used to find duplicates. If another torrent is already running with the same UUID as the one being added, it will be considered a duplicate. This is mainly useful for RSS feed items which has UUIDs specified.

source_feed_url

should point to the URL of the RSS feed this torrent comes from, if it comes from an RSS feed.

flags

flags controlling aspects of this torrent and how it's added. See flags_t for details.

info_hash

set this to the info hash of the torrent to add in case the info-hash is the only known property of the torrent. i.e. you don't have a .torrent file nor a magnet link.

max_uploads max_connections upload_limit download_limit

max_uploads, max_connections, upload_limit, download_limit correspond to the set_max_uploads(), set_max_connections(), set_upload_limit() and set_download_limit() functions on torrent_handle. These values let you initialize these settings when the torrent is added, instead of calling these functions immediately following adding it.

-1 means unlimited on these settings just like their counterpart functions on torrent_handle

cache_status()

cache_status ();

initializes all counters to 0

write_cache_size

the number of blocks in the cache used for write cache

read_cache_size

the number of 16KiB blocks in the read cache.

pinned_blocks

the number of blocks with a refcount > 0, i.e. they may not be evicted

total_used_buffers

the total number of buffers currently in use. This includes the read/write disk cache as well as send and receive buffers used in peer connections.

average_read_time

the time read jobs takes on average to complete (not including the time in the queue), in microseconds. This only measures read cache misses.

average_write_time

the time write jobs takes to complete, on average, in microseconds. This does not include the time the job sits in the disk job queue or in the write cache, only blocks that are flushed to disk.

average_hash_time average_job_time

the time hash jobs takes to complete on average, in microseconds. Hash jobs include running SHA-1 on the data (which for the most part is done incrementally) and sometimes reading back parts of the piece. It also includes checking files without valid resume data.

cumulative_job_time cumulative_read_time cumulative_write_time cumulative_hash_time

the number of milliseconds spent in all disk jobs, and specific ones since the start of the session. Times are specified in milliseconds

total_read_back

the number of blocks that had to be read back from disk because they were flushed before the SHA-1 hash got to hash them. If this is large, a larger cache could significantly improve performance

read_queue_size

number of read jobs in the disk job queue

blocked_jobs

number of jobs blocked because of a fence

queued_jobs

number of jobs waiting to be issued (m_to_issue) average over 30 seconds

peak_queued

largest ever seen number of queued jobs

pending_jobs

number of jobs waiting to complete (m_pending) average over 30 seconds

num_jobs

total number of disk job objects allocated right now

num_read_jobs

total number of disk read job objects allocated right now

num_write_jobs

total number of disk write job objects allocated right now

arc_mru_size arc_mru_ghost_size arc_mfu_size arc_mfu_ghost_size arc_write_size arc_volatile_size

ARC cache stats. All of these counters are in number of pieces not blocks. A piece does not necessarily correspond to a certain number of blocks. The pieces in the ghost list never have any blocks in them

num_writing_threads

the number of threads currently writing to disk

num_fence_jobs[disk_io_job

counts only fence jobs that are currently blocking jobs not fences that are themself blocked

session_proxy()

session_proxy ();

default constructor, does not refer to any session implementation object.

session()

session (fingerprint const& print = fingerprint("LT"
      , LIBTORRENT_VERSION_MAJOR, LIBTORRENT_VERSION_MINOR, 0, 0)
      , int flags = start_default_features | add_default_plugins
      , boost::uint32_t alert_mask = alert::error_notification
      TORRENT_LOGPATH_ARG_DEFAULT);
session (settings_pack const& pack
      , fingerprint const& print = fingerprint("LT"
      , LIBTORRENT_VERSION_MAJOR, LIBTORRENT_VERSION_MINOR, 0, 0)
      , int flags = start_default_features | add_default_plugins);
session (fingerprint const& print
      , std::pair<int, int> listen_port_range
      , char const* listen_interface = "0.0.0.0"
      , int flags = start_default_features | add_default_plugins
      , int alert_mask = alert::error_notification
      TORRENT_LOGPATH_ARG_DEFAULT);

TODO: 3 could the fingerprint be a setting as well? And should the settings_pack be optional?

~session()

~session ();

The destructor of session will notify all trackers that our torrents have been shut down. If some trackers are down, they will time out. All this before the destructor of session returns. So, it's advised that any kind of interface (such as windows) are closed before destructing the session object. Because it can take a few second for it to finish. The timeout can be set with apply_settings().

load_state() save_state()

void load_state (lazy_entry const& e);
void save_state (entry& e, boost::uint32_t flags = 0xffffffff) const;

loads and saves all session settings, including dht_settings, encryption settings and proxy settings. save_state writes all keys to the entry that's passed in, which needs to either not be initialized, or initialized as a dictionary.

load_state expects a lazy_entry which can be built from a bencoded buffer with lazy_bdecode().

The flags arguments passed in to save_state can be used to filter which parts of the session state to save. By default, all state is saved (except for the individual torrents). see save_state_flags_t

get_torrent_status() refresh_torrent_status()

void refresh_torrent_status (std::vector<torrent_status>* ret
      , boost::uint32_t flags = 0) const;
void get_torrent_status (std::vector<torrent_status>* ret
      , boost::function<bool(torrent_status const&)> const& pred
      , boost::uint32_t flags = 0) const;

get_torrent_status returns a vector of the torrent_status for every torrent which satisfies pred, which is a predicate function which determines if a torrent should be included in the returned set or not. Returning true means it should be included and false means excluded. The flags argument is the same as to torrent_handle::status(). Since pred is guaranteed to be called for every torrent, it may be used to count the number of torrents of different categories as well.

refresh_torrent_status takes a vector of torrent_status structs (for instance the same vector that was returned by get_torrent_status() ) and refreshes the status based on the handle member. It is possible to use this function by first setting up a vector of default constructed torrent_status objects, only initializing the handle member, in order to request the torrent status for multiple torrents in a single call. This can save a significant amount of time if you have a lot of torrents.

Any torrent_status object whose handle member is not referring to a valid torrent are ignored.

post_torrent_updates()

void post_torrent_updates ();

This functions instructs the session to post the state_update_alert, containing the status of all torrents whose state changed since the last time this function was called.

Only torrents who has the state subscription flag set will be included. This flag is on by default. See add_torrent_params.

post_session_stats()

void post_session_stats ();

This function will post a session_stats_alert object, containing a snapshot of the performance counters from the internals of libtorrent. To interpret these counters, query the session via session_stats_metrics().

For more information, see the session statistics section.

find_torrent() get_torrents()

torrent_handle find_torrent (sha1_hash const& info_hash) const;
std::vector<torrent_handle> get_torrents () const;

find_torrent() looks for a torrent with the given info-hash. In case there is such a torrent in the session, a torrent_handle to that torrent is returned. In case the torrent cannot be found, an invalid torrent_handle is returned.

See torrent_handle::is_valid() to know if the torrent was found or not.

get_torrents() returns a vector of torrent_handles to all the torrents currently in the session.

add_torrent() async_add_torrent()

void async_add_torrent (add_torrent_params const& params);
torrent_handle add_torrent (add_torrent_params const& params, error_code& ec);
torrent_handle add_torrent (add_torrent_params const& params);

You add torrents through the add_torrent() function where you give an object with all the parameters. The add_torrent() overloads will block until the torrent has been added (or failed to be added) and returns an error code and a torrent_handle. In order to add torrents more efficiently, consider using async_add_torrent() which returns immediately, without waiting for the torrent to add. Notification of the torrent being added is sent as add_torrent_alert.

The overload that does not take an error_code throws an exception on error and is not available when building without exception support. The torrent_handle returned by add_torrent() can be used to retrieve information about the torrent's progress, its peers etc. It is also used to abort a torrent.

If the torrent you are trying to add already exists in the session (is either queued for checking, being checked or downloading) add_torrent() will throw libtorrent_exception which derives from std::exception unless duplicate_is_error is set to false. In that case, add_torrent() will return the handle to the existing torrent.

all torrent_handles must be destructed before the session is destructed!

abort()

session_proxy abort ();

In case you want to destruct the session asynchrounously, you can request a session destruction proxy. If you don't do this, the destructor of the session object will block while the trackers are contacted. If you keep one session_proxy to the session when destructing it, the destructor will not block, but start to close down the session, the destructor of the proxy will then synchronize the threads. So, the destruction of the session is performed from the session destructor call until the session_proxy destructor call. The session_proxy does not have any operations on it (since the session is being closed down, no operations are allowed on it). The only valid operation is calling the destructor:

class session_proxy
{
public:
        session_proxy();
        ~session_proxy()
};

pause() resume() is_paused()

void resume ();
void pause ();
bool is_paused () const;

Pausing the session has the same effect as pausing every torrent in it, except that torrents will not be resumed by the auto-manage mechanism. Resuming will restore the torrents to their previous paused state. i.e. the session pause state is separate from the torrent pause state. A torrent is inactive if it is paused or if the session is paused.

set_load_function()

void set_load_function (user_load_function_t fun);

This function enables dynamic loading of torrent files. When a torrent is unloaded but needs to be availabe in memory, this function is called from within the libtorrent network thread. From within this thread, you can not use any of the public APIs of libtorrent itself. The the info-hash of the torrent is passed in to the function and it is expected to fill in the passed in vector<char> with the .torrent file corresponding to it.

If there is an error loading the torrent file, the error_code (ec) should be set to reflect the error. In such case, the torrent itself is stopped and set to an error state with the corresponding error code.

Given that the function is called from the internal network thread of libtorrent, it's important to not stall. libtorrent will not be able to send nor receive any data until the function call returns.

The signature of the function to pass in is:

void fun(sha1_hash const& info_hash, std::vector<char>& buf, error_code& ec);

status()

session_status status () const;

returns session wide-statistics and status. For more information, see the session_status struct.

get_cache_info()

void get_cache_info (cache_status* ret, torrent_handle h = torrent_handle(), int flags = 0) const;

Fills in the cache_status struct with information about the given torrent. If flags is session::disk_cache_no_pieces the cache_status::pieces field will not be set. This may significantly reduce the cost of this call.

add_feed()

feed_handle add_feed (feed_settings const& feed);

This adds an RSS feed to the session. The feed will be refreshed regularly and optionally add all torrents from the feed, as they appear.

Before adding the feed, you must set the url field to the feed's url. It may point to an RSS or an atom feed. The returned feed_handle is a handle which is used to interact with the feed, things like forcing a refresh or querying for information about the items in the feed. For more information, see feed_handle.

remove_feed()

void remove_feed (feed_handle h);

Removes a feed from being watched by the session. When this call returns, the feed handle is invalid and won't refer to any feed.

get_feeds()

void get_feeds (std::vector<feed_handle>& f) const;

Returns a list of all RSS feeds that are being watched by the session.

is_dht_running() set_dht_settings()

bool is_dht_running () const;
void set_dht_settings (dht_settings const& settings);

set_dht_settings sets some parameters availavle to the dht node. See dht_settings for more information.

is_dht_running() returns true if the DHT support has been started and false otherwise.

add_dht_router() add_dht_node()

void add_dht_router (std::pair<std::string, int> const& node);
void add_dht_node (std::pair<std::string, int> const& node);

add_dht_node takes a host name and port pair. That endpoint will be pinged, and if a valid DHT reply is received, the node will be added to the routing table.

add_dht_router adds the given endpoint to a list of DHT router nodes. If a search is ever made while the routing table is empty, those nodes will be used as backups. Nodes in the router node list will also never be added to the regular routing table, which effectively means they are only used for bootstrapping, to keep the load off them.

An example routing node that you could typically add is router.bittorrent.com.

dht_get_item()

void dht_get_item (sha1_hash const& target);

query the DHT for an immutable item at the target hash. the result is posted as a dht_immutable_item_alert.

dht_get_item()

void dht_get_item (boost::array<char, 32> key
      , std::string salt = std::string());

query the DHT for a mutable item under the public key key. this is an ed25519 key. salt is optional and may be left as an empty string if no salt is to be used. if the item is found in the DHT, a dht_mutable_item_alert is posted.

dht_put_item()

sha1_hash dht_put_item (entry data);

store the given bencoded data as an immutable item in the DHT. the returned hash is the key that is to be used to look the item up agan. It's just the sha-1 hash of the bencoded form of the structure.

dht_put_item()

void dht_put_item (boost::array<char, 32> key
      , boost::function<void(entry&, boost::array<char,64>&
      , boost::uint64_t&, std::string const&)> cb
      , std::string salt = std::string());

store an immutable item. The key is the public key the blob is to be stored under. The optional salt argument is a string that is to be mixed in with the key when determining where in the DHT the value is to be stored. The callback function is called from within the libtorrent network thread once we've found where to store the blob, possibly with the current value stored under the key. The values passed to the callback functions are:

entry& value

the current value stored under the key (may be empty). Also expected to be set to the value to be stored by the function.

boost::array<char,64>& signature

the signature authenticating the current value. This may be zeroes if there is currently no value stored. The functon is expected to fill in this buffer with the signature of the new value to store. To generate the signature, you may want to use the sign_mutable_item function.

boost::uint64_t& seq

current sequence number. May be zero if there is no current value. The function is expected to set this to the new sequence number of the value that is to be stored. Sequence numbers must be monotonically increasing. Attempting to overwrite a value with a lower or equal sequence number will fail, even if the signature is correct.

std::string const& salt

this is the salt that was used for this put call.

Since the callback function cb is called from within libtorrent, it is critical to not perform any blocking operations. Ideally not even locking a mutex. Pass any data required for this function along with the function object's context and make the function entirely self-contained. The only reason data blobs' values are computed via a function instead of just passing in the new value is to avoid race conditions. If you want to update the value in the DHT, you must first retrieve it, then modify it, then write it back. The way the DHT works, it is natural to always do a lookup before storing and calling the callback in between is convenient.

add_extension()

void add_extension (boost::function<boost::shared_ptr<torrent_plugin>(
      torrent*, void*)> ext);
void add_extension (boost::shared_ptr<plugin> ext);

This function adds an extension to this session. The argument is a function object that is called with a torrent* and which should return a boost::shared_ptr<torrent_plugin>. To write custom plugins, see libtorrent plugins. For the typical bittorrent client all of these extensions should be added. The main plugins implemented in libtorrent are:

metadata extension

Allows peers to download the metadata (.torren files) from the swarm directly. Makes it possible to join a swarm with just a tracker and info-hash.

#include <libtorrent/extensions/metadata_transfer.hpp>
ses.add_extension(&libtorrent::create_metadata_plugin);

uTorrent metadata

Same as metadata extension but compatible with uTorrent.

#include <libtorrent/extensions/ut_metadata.hpp>
ses.add_extension(&libtorrent::create_ut_metadata_plugin);

uTorrent peer exchange

Exchanges peers between clients.

#include <libtorrent/extensions/ut_pex.hpp>
ses.add_extension(&libtorrent::create_ut_pex_plugin);

smart ban plugin

A plugin that, with a small overhead, can ban peers that sends bad data with very high accuracy. Should eliminate most problems on poisoned torrents.

#include <libtorrent/extensions/smart_ban.hpp>
ses.add_extension(&libtorrent::create_smart_ban_plugin);

load_asnum_db() load_country_db() as_for_ip()

void load_country_db (char const* file);
void load_asnum_db (char const* file);
int as_for_ip (address const& addr);

These functions are not available if TORRENT_DISABLE_GEO_IP is defined. They expects a path to the MaxMind ASN database and MaxMind GeoIP database respectively. This will be used to look up which AS and country peers belong to.

as_for_ip returns the AS number for the IP address specified. If the IP is not in the database or the ASN database is not loaded, 0 is returned.

get_ip_filter() set_ip_filter()

ip_filter get_ip_filter () const;
void set_ip_filter (ip_filter const& f);

Sets a filter that will be used to reject and accept incoming as well as outgoing connections based on their originating ip address. The default filter will allow connections to any ip address. To build a set of rules for which addresses are accepted and not, see ip_filter.

Each time a peer is blocked because of the IP filter, a peer_blocked_alert is generated. get_ip_filter() Returns the ip_filter currently in the session. See ip_filter.

set_port_filter()

void set_port_filter (port_filter const& f);

apply port_filter f to incoming and outgoing peers. a port filter will reject making outgoing peer connections to certain remote ports. The main intention is to be able to avoid triggering certain anti-virus software by connecting to SMTP, FTP ports.

set_peer_id() id()

peer_id id () const;
void set_peer_id (peer_id const& pid);

sets and gets the raw peer ID used by libtorrent. When anonymous mode is set the peer ID is randomized per peer anyway.

set_key()

void set_key (int key);

sets the key sent to trackers. If it's not set, it is initialized by libtorrent. The key may be used by the tracker to identify the peer potentially across you changing your IP.

listen_port() ssl_listen_port() is_listening()

bool is_listening () const;
unsigned short listen_port () const;
unsigned short ssl_listen_port () const;

is_listening() will tell you whether or not the session has successfully opened a listening port. If it hasn't, this function will return false, and then you can set a new settings_pack::listen_interfaces to try another interface and port to bind to.

listen_port() returns the port we ended up listening on. If the port specified in settings_pack::listen_interfaces failed, libtorrent will try to bind to the next port, and so on. If it fails settings_pack::max_retry_port_bind times, it will bind to port 0 (meaning the OS picks the port). The only way to know which port it ended up binding to is to ask for it by calling listen_port().

If all ports in the specified range fails to be opened for listening, libtorrent will try to use port 0 (which tells the operating system to pick a port that's free). If that still fails you may see a listen_failed_alert with port 0 even if you didn't ask to listen on it.

It is possible to prevent libtorrent from binding to port 0 by passing in the flag session::no_system_port in the flags argument.

The interface parameter can also be a hostname that will resolve to the device you want to listen on. If you don't specify an interface, libtorrent may attempt to listen on multiple interfaces (typically 0.0.0.0 and ::). This means that if your IPv6 interface doesn't work, you may still see a listen_failed_alert, even though the IPv4 port succeeded.

The flags parameter can either be 0 or session::listen_reuse_address, which will set the reuse address socket option on the listen socket(s). By default, the listen socket does not use reuse address. If you're running a service that needs to run on a specific port no matter if it's in use, set this flag.

set_peer_class_filter()

void set_peer_class_filter (ip_filter const& f);

Sets the peer class filter for this session. All new peer connections will take this into account and be added to the peer classes specified by this filter, based on the peer's IP address.

The ip-filter essentially maps an IP -> uint32. Each bit in that 32 bit integer represents a peer class. The least significant bit represents class 0, the next bit class 1 and so on.

For more info, see ip_filter.

For example, to make all peers in the range 200.1.1.0 - 200.1.255.255 belong to their own peer class, apply the following filter:

ip_filter f;
int my_class = ses.create_peer_class("200.1.x.x IP range");
f.add_rule(address_v4::from_string("200.1.1.0")
        , address_v4::from_string("200.1.255.255")
        , 1 << my_class);
ses.set_peer_class_filter(f);

This setting only applies to new connections, it won't affect existing peer connections.

This function is limited to only peer class 0-31, since there are only 32 bits in the IP range mapping. Only the set bits matter; no peer class will be removed from a peer as a result of this call, peer classes are only added.

The peer_class argument cannot be greater than 31. The bitmasks representing peer classes in the peer_class_filter are 32 bits.

For more information, see peer classes.

set_peer_class_type_filter()

void set_peer_class_type_filter (peer_class_type_filter const& f);

Sets and gets the peer class type filter. This is controls automatic peer class assignments to peers based on what kind of socket it is.

It does not only support assigning peer classes, it also supports removing peer classes based on socket type.

The order of these rules being applied are:

1. peer-class IP filter
2. peer-class type filter, removing classes
3. peer-class type filter, adding classes

For more information, see peer classes. TODO: add get_peer_class_type_filter() as well

create_peer_class()

int create_peer_class (char const* name);

Creates a new peer class (see peer classes) with the given name. The returned integer is the new peer class' identifier. Peer classes may have the same name, so each invocation of this function creates a new class and returns a unique identifier.

Identifiers are assigned from low numbers to higher. So if you plan on using certain peer classes in a call to set_peer_class_filter(), make sure to create those early on, to get low identifiers.

For more information on peer classes, see peer classes.

delete_peer_class()

void delete_peer_class (int cid);

This call dereferences the reference count of the specified peer class. When creating a peer class it's automatically referenced by 1. If you want to recycle a peer class, you may call this function. You may only call this function once per peer class you create. Calling it more than once for the same class will lead to memory corruption.

Since peer classes are reference counted, this function will not remove the peer class if it's still assigned to torrents or peers. It will however remove it once the last peer and torrent drops their references to it.

There is no need to call this function for custom peer classes. All peer classes will be properly destructed when the session object destructs.

For more information on peer classes, see peer classes.

get_peer_class() set_peer_class()

peer_class_info get_peer_class (int cid);
void set_peer_class (int cid, peer_class_info const& pci);

These functions queries information from a peer class and updates the configuration of a peer class, respectively.

cid must refer to an existing peer class. If it does not, the return value of get_peer_class() is undefined.

set_peer_class() sets all the information in the peer_class_info object in the specified peer class. There is no option to only update a single property.

A peer or torrent balonging to more than one class, the highest priority among any of its classes is the one that is taken into account.

For more information, see peer classes.

remove_torrent()

void remove_torrent (const torrent_handle& h, int options = 0);

remove_torrent() will close all peer connections associated with the torrent and tell the tracker that we've stopped participating in the swarm. This operation cannot fail. When it completes, you will receive a torrent_removed_alert.

The optional second argument options can be used to delete all the files downloaded by this torrent. To do so, pass in the value session::delete_files. The removal of the torrent is asyncronous, there is no guarantee that adding the same torrent immediately after it was removed will not throw a libtorrent_exception exception. Once the torrent is deleted, a torrent_deleted_alert is posted.

get_settings() apply_settings()

aux::session_settings get_settings () const;
void apply_settings (settings_pack const& s);

Applies the settings specified by the settings_pack s. This is an asynchronous operation that will return immediately and actually apply the settings to the main thread of libtorrent some time later.

pop_alert() pop_alerts() wait_for_alert()

void pop_alerts (std::deque<alert*>* alerts);
std::auto_ptr<alert> pop_alert ();
alert const* wait_for_alert (time_duration max_wait);

pop_alert() is used to ask the session if any errors or events has occurred. With settings_pack::alert_mask you can filter which alerts to receive through pop_alert(). For information about the alert categories, see alerts.

pop_alerts() pops all pending alerts in a single call. In high performance environments with a very high alert churn rate, this can save significant amount of time compared to popping alerts one at a time. Each call requires one round-trip to the network thread. If alerts are produced in a higher rate than they can be popped (when popped one at a time) it's easy to get stuck in an infinite loop, trying to drain the alert queue. Popping the entire queue at once avoids this problem.

However, the pop_alerts function comes with significantly more responsibility. You pass in an empty std::dequeue<alert*> to it. If it's not empty, all elements in it will be deleted and then cleared. All currently pending alerts are returned by being swapped into the passed in container. The responsibility of deleting the alerts is transferred to the caller. This means you need to call delete for each item in the returned dequeue. It's probably a good idea to delete the alerts as you handle them, to save one extra pass over the dequeue.

Alternatively, you can pass in the same container the next time you call pop_alerts.

wait_for_alert blocks until an alert is available, or for no more than max_wait time. If wait_for_alert returns because of the time-out, and no alerts are available, it returns 0. If at least one alert was generated, a pointer to that alert is returned. The alert is not popped, any subsequent calls to wait_for_alert will return the same pointer until the alert is popped by calling pop_alert. This is useful for leaving any alert dispatching mechanism independent of this blocking call, the dispatcher can be called and it can pop the alert independently.

In the python binding, wait_for_alert takes the number of milliseconds to wait as an integer.

To control the max number of alerts that's queued by the session, see session_settings::alert_queue_size.

save_resume_data_alert and save_resume_data_failed_alert are always posted, regardelss of the alert mask.

set_alert_dispatch()

void set_alert_dispatch (boost::function<void(std::auto_ptr<alert>)> const& fun);

This sets a function to be called (from within libtorrent's netowrk thread) every time an alert is posted. Since the function (fun) is run in libtorrent's internal thread, it may not call any of libtorrent's external API functions. Doing so results in a dead lock.

The main intention with this function is to support integration with platform-dependent message queues or signalling systems. For instance, on windows, one could post a message to an HNWD or on linux, write to a pipe or an eventfd.

add_port_mapping() delete_port_mapping()

void delete_port_mapping (int handle);
int add_port_mapping (protocol_type t, int external_port, int local_port);

add_port_mapping adds a port forwarding on UPnP and/or NAT-PMP, whichever is enabled. The return value is a handle referring to the port mapping that was just created. Pass it to delete_port_mapping() to remove it.

enum save_state_flags_t

Declared in "libtorrent/session.hpp"

enum options_t

Declared in "libtorrent/session.hpp"

enum session_flags_t

Declared in "libtorrent/session.hpp"

enum protocol_type

Declared in "libtorrent/session.hpp"

find_metric_idx()

Declared in "libtorrent/session.hpp"

int find_metric_idx (char const* name);

given a name of a metric, this function returns the counter index of it, or -1 if it could not be found. The counter index is the index into the values array returned by session_stats_alert.

session_stats_metrics()

Declared in "libtorrent/session.hpp"

std::vector<stats_metric> session_stats_metrics ();

This free function returns the list of available metrics exposed by libtorrent's statistics API. Each metric has a name and a value index. The value index is the index into the array in session_stats_alert where this metric's value can be found when the session stats is sampled (by calling post_session_stats()).