separate the main thread and the io_service from session_impl. The io_service object is now simply run() in the main thread, all initialization is done by posting messages to it. This generalizes session_impl to some degree, enables future expansion to run in multiple threads (although, the peers and torrents don't support this). This patch also makes it possible to pass in a third party io_service to the session, but at this point that's mostly useful for tests, as it's not well supported

include/libtorrent/aux_/session_impl.hpp

@@ -179,10 +179,9 @@ namespace libtorrent
 			typedef std::map<sha1_hash, boost::shared_ptr<torrent> > torrent_map;
 #endif
 
-			session_impl();
+			session_impl(io_service& ios);
 			virtual ~session_impl();
 
-			void init();
 			void start_session(settings_pack const& pack);
 
 			void set_load_function(user_load_function_t fun)
@@ -205,10 +204,7 @@ namespace libtorrent
 			bool m_posting_torrent_updates;
 #endif
 
-			void main_thread();
-
 			void open_listen_port();
-			void init_settings();
 
 			torrent_peer_allocator_interface* get_peer_allocator() { return &m_peer_allocator; }
 
@@ -608,7 +604,10 @@ namespace libtorrent
 
 			peer_class_pool m_classes;
 
-			// TODO: 2 fix this
+			void init(boost::shared_ptr<settings_pack> pack);
+
+			// TODO: 3 fix this. all this should not be public. start by making
+			// everything that doesn't have to be public private.
 		public:
 
 			void submit_disk_jobs();
@@ -679,10 +678,7 @@ namespace libtorrent
 			boost::pool<> m_send_buffers;
 #endif
 
-			// this is where all active sockets are stored.
+			io_service& m_io_service;
-			// the selector can sleep while there's no activity on
-			// them
-			mutable io_service m_io_service;
 
 #ifdef TORRENT_USE_OPENSSL
 			// this is a generic SSL context used when talking to
@@ -1185,13 +1181,6 @@ namespace libtorrent
 			// into fewer network writes, saving CPU and possibly
 			// ending up sending larger network packets
 			std::vector<peer_connection*> m_delayed_uncorks;
-
-			// the main working thread
-			boost::scoped_ptr<thread> m_thread;
-
-#if TORRENT_USE_ASSERTS && defined BOOST_HAS_PTHREADS
-			pthread_t m_network_thread;
-#endif
 		};
 
 #ifndef TORRENT_DISABLE_LOGGING

include/libtorrent/session.hpp

@@ -54,9 +54,12 @@ POSSIBILITY OF SUCH DAMAGE.
 #include "libtorrent/peer_class.hpp"
 #include "libtorrent/peer_class_type_filter.hpp"
 #include "libtorrent/build_config.hpp"
+#include "libtorrent/settings_pack.hpp"
+#include "libtorrent/io_service.hpp"
 
 #include "libtorrent/storage.hpp"
 #include "libtorrent/session_settings.hpp"
+#include "libtorrent/thread.hpp"
 
 #ifndef TORRENT_NO_DEPRECATE
 #include "libtorrent/rss.hpp"
@@ -143,9 +146,18 @@ namespace libtorrent
 		// default constructor, does not refer to any session
 		// implementation object.
 		session_proxy() {}
+		~session_proxy();
 	private:
-		session_proxy(boost::shared_ptr<aux::session_impl> impl)
+		session_proxy(
-			: m_impl(impl) {}
+			boost::shared_ptr<io_service> ios
+			, boost::shared_ptr<thread> t
+			, boost::shared_ptr<aux::session_impl> impl)
+			: m_io_service(ios)
+			, m_thread(t)
+			, m_impl(impl)
+		{}
+		boost::shared_ptr<io_service> m_io_service;
+		boost::shared_ptr<thread> m_thread;
 		boost::shared_ptr<aux::session_impl> m_impl;
 	};
 
@@ -165,26 +177,47 @@ namespace libtorrent
 	{
 	public:
 
-		// If the fingerprint in the first overload is omited, the client will get
+		// Constructs the session obects which acts as the container of torrents.
-		// a default fingerprint stating the version of libtorrent. The
+		// It provides configuration options across torrents (such as rate limits,
-		// fingerprint is a short string that will be used in the peer-id to
+		// disk cache, ip filter etc.). In order to avoid a race condition between
-		// identify the client and the client's version. For more details see the
+		// starting the session and configuring it, you can pass in a
-		// fingerprint class.
+		// settings_pack object. Its settings will take effect before the session
+		// starts up.
 		// 
-		// The flags parameter can be used to start default features (upnp &
+		// The ``flags`` parameter can be used to start default features (upnp &
 		// nat-pmp) and default plugins (ut_metadata, ut_pex and smart_ban). The
 		// default is to start those features. If you do not want them to start,
 		// pass 0 as the flags parameter.
-		// 
-		// The ``alert_mask`` is the same mask that you would send to
-		// set_alert_mask().
-
 		session(settings_pack const& pack
 			, int flags = start_default_features | add_default_plugins)
 		{
 			TORRENT_CFG();
-			start(flags, pack);
+			start(flags, pack, NULL);
 		}
+
+		// overload of the constructor that takes an external io_service to run
+		// the session object on. This is primarily useful for tests that may want
+		// to run multiple sessions on a single io_service, or low resource
+		// systems where additional threads are expensive and sharing an
+		// io_service with other events is fine.
+		// 
+		// .. warning::
+		// 	The session object does not cleanly terminate with an external
+		// 	io_service. The io_service::run() call _must_ have returned before
+		// 	it's safe to destruct the session. Which means you *MUST* call
+		// 	session::abort() and save the session_proxy first, then destruct the
+		// 	session object, then sync withthe io_service, then destruct the
+		// 	session_proxy object.
+		session(settings_pack const& pack
+			, io_service& ios
+			, int flags = start_default_features | add_default_plugins)
+		{
+			TORRENT_CFG();
+			start(flags, pack, &ios);
+		}
+
+#ifndef TORRENT_NO_DEPRECATE
+		TORRENT_DEPRECATED
 		session(fingerprint const& print = fingerprint("LT"
 			, LIBTORRENT_VERSION_MAJOR, LIBTORRENT_VERSION_MINOR, 0, 0)
 			, int flags = start_default_features | add_default_plugins
@@ -192,9 +225,6 @@ namespace libtorrent
 		{
 			TORRENT_CFG();
 			settings_pack pack;
-			// TODO: 2 the two second constructors here should probably
-			// be deprecated in favor of the more generic one that just
-			// takes a settings_pack and a string
 			pack.set_int(settings_pack::alert_mask, alert_mask);
 			pack.set_str(settings_pack::peer_fingerprint, print.to_string());
 			if ((flags & start_default_features) == 0)
@@ -205,8 +235,10 @@ namespace libtorrent
 				pack.set_bool(settings_pack::enable_dht, false);
 			}
 
-			start(flags, pack);
+			start(flags, pack, NULL);
 		}
+
+		TORRENT_DEPRECATED
 		session(fingerprint const& print
 			, std::pair<int, int> listen_port_range
 			, char const* listen_interface = "0.0.0.0"
@@ -232,8 +264,9 @@ namespace libtorrent
 				pack.set_bool(settings_pack::enable_lsd, false);
 				pack.set_bool(settings_pack::enable_dht, false);
 			}
-			start(flags, pack);
+			start(flags, pack, NULL);
 		}
+#endif // TORRENT_NO_DEPRECATE
 
 		// The destructor of session will notify all trackers that our torrents
 		// have been shut down. If some trackers are down, they will time out.
@@ -432,7 +465,7 @@ namespace libtorrent
 		// 		session_proxy();
 		// 		~session_proxy()
 		// 	};
-		session_proxy abort() { return session_proxy(m_impl); }
+		session_proxy abort() { return session_proxy(m_io_service, m_thread, m_impl); }
 
 		// Pausing the session has the same effect as pausing every torrent in
 		// it, except that torrents will not be resumed by the auto-manage
@@ -1218,10 +1251,12 @@ namespace libtorrent
 
 	private:
 
-		void start(int flags, settings_pack const& pack);
+		void start(int flags, settings_pack const& pack, io_service* ios);
 
 		// data shared between the main thread
 		// and the working thread
+		boost::shared_ptr<io_service> m_io_service;
+		boost::shared_ptr<thread> m_thread;
 		boost::shared_ptr<aux::session_impl> m_impl;
 	};
 

src/session.cpp

@@ -389,7 +389,7 @@ namespace libtorrent
 	{ throw; }
 #endif
 
-	void session::start(int flags, settings_pack const& pack)
+	void session::start(int flags, settings_pack const& pack, io_service* ios)
 	{
 #if defined _MSC_VER && defined TORRENT_DEBUG
 		// workaround for microsofts
@@ -398,7 +398,17 @@ namespace libtorrent
 		::_set_se_translator(straight_to_debugger);
 #endif
 
-		m_impl.reset(new session_impl());
+		bool internal_executor = ios == NULL;
+
+		if (internal_executor)
+		{
+			// the user did not provide an executor, we have to use our own
+			m_io_service = boost::make_shared<io_service>();
+			ios = m_io_service.get();
+		}
+
+		m_impl = boost::make_shared<session_impl>(boost::ref(*ios));
+
 #ifndef TORRENT_DISABLE_EXTENSIONS
 		if (flags & add_default_plugins)
 		{
@@ -409,6 +419,13 @@ namespace libtorrent
 #endif
 
 		m_impl->start_session(pack);
+
+		if (internal_executor)
+		{
+			// start a thread for the message pump
+			m_thread = boost::make_shared<thread>(boost::bind(&io_service::run
+				, m_io_service.get()));
+		}
 	}
 
 	session::~session()
@@ -416,13 +433,10 @@ namespace libtorrent
 		aux::dump_call_profile();
 
 		TORRENT_ASSERT(m_impl);
-		// if there is at least one destruction-proxy
+		TORRENT_ASYNC_CALL(abort);
-		// abort the session and let the destructor
+
-		// of the proxy to syncronize
+		if (m_thread && m_thread.unique())
-		if (!m_impl.unique())
+			m_thread->join();
-		{
-			TORRENT_ASYNC_CALL(abort);
-		}
 	}
 
 	void session::save_state(entry& e, boost::uint32_t flags) const
@@ -1278,5 +1292,10 @@ namespace libtorrent
 	session_settings::~session_settings() {}
 #endif // TORRENT_NO_DEPRECATE
 
+	session_proxy::~session_proxy()
+	{
+		if (m_thread && m_thread.unique())
+			m_thread->join();
+	}
 }
 

src/session_impl.cpp

@@ -336,13 +336,13 @@ namespace aux {
 	}
 #endif
 
-	session_impl::session_impl()
+	session_impl::session_impl(io_service& ios)
 		:
 #ifndef TORRENT_DISABLE_POOL_ALLOCATOR
 		m_send_buffers(send_buffer_size())
 		,
 #endif
-		m_io_service()
+		m_io_service(ios)
 #ifdef TORRENT_USE_OPENSSL
 		, m_ssl_ctx(m_io_service, asio::ssl::context::sslv23)
 #endif
@@ -548,18 +548,54 @@ namespace aux {
 #endif
 
 		boost::shared_ptr<settings_pack> copy = boost::make_shared<settings_pack>(pack);
-		m_io_service.post(boost::bind(&session_impl::apply_settings_pack, this, copy));
+		m_io_service.post(boost::bind(&session_impl::init, this, copy));
-		// call update_* after settings set initialized
-		m_io_service.post(boost::bind(&session_impl::init_settings, this));
-
-#ifndef TORRENT_DISABLE_LOGGING
-		session_log(" spawning network thread");
-#endif
-		m_thread.reset(new thread(boost::bind(&session_impl::main_thread, this)));
 	}
 
-	void session_impl::init_settings()
+	void session_impl::init(boost::shared_ptr<settings_pack> pack)
 	{
+		// this is a debug facility
+		// see single_threaded in debug.hpp
+		thread_started();
+
+		TORRENT_ASSERT(is_single_thread());
+
+#ifndef TORRENT_DISABLE_LOGGING
+		session_log(" *** session thread init");
+#endif
+
+		// this is where we should set up all async operations. This
+		// is called from within the network thread as opposed to the
+		// constructor which is called from the main thread
+
+#if defined TORRENT_ASIO_DEBUGGING
+		async_inc_threads();
+		add_outstanding_async("session_impl::on_tick");
+#endif
+		error_code ec;
+		m_io_service.post(boost::bind(&session_impl::on_tick, this, ec));
+
+#if defined TORRENT_ASIO_DEBUGGING
+		add_outstanding_async("session_impl::on_lsd_announce");
+#endif
+		int delay = (std::max)(m_settings.get_int(settings_pack::local_service_announce_interval)
+			/ (std::max)(int(m_torrents.size()), 1), 1);
+		m_lsd_announce_timer.expires_from_now(seconds(delay), ec);
+		m_lsd_announce_timer.async_wait(
+			boost::bind(&session_impl::on_lsd_announce, this, _1));
+		TORRENT_ASSERT(!ec);
+
+#ifndef TORRENT_DISABLE_DHT
+		update_dht_announce_interval();
+#endif
+
+#ifndef TORRENT_DISABLE_LOGGING
+		session_log(" done starting session");
+#endif
+
+		apply_settings_pack(pack);
+
+		// call update_* after settings set initialized
+
 #ifndef TORRENT_NO_DEPRECATE
 		update_local_download_rate();
 		update_local_upload_rate();
@@ -641,42 +677,6 @@ namespace aux {
 		}
 	}
 
-	void session_impl::init()
-	{
-#ifndef TORRENT_DISABLE_LOGGING
-		session_log(" *** session thread init");
-#endif
-
-		// this is where we should set up all async operations. This
-		// is called from within the network thread as opposed to the
-		// constructor which is called from the main thread
-
-#if defined TORRENT_ASIO_DEBUGGING
-		async_inc_threads();
-		add_outstanding_async("session_impl::on_tick");
-#endif
-		error_code ec;
-		m_io_service.post(boost::bind(&session_impl::on_tick, this, ec));
-
-#if defined TORRENT_ASIO_DEBUGGING
-		add_outstanding_async("session_impl::on_lsd_announce");
-#endif
-		int delay = (std::max)(m_settings.get_int(settings_pack::local_service_announce_interval)
-			/ (std::max)(int(m_torrents.size()), 1), 1);
-		m_lsd_announce_timer.expires_from_now(seconds(delay), ec);
-		m_lsd_announce_timer.async_wait(
-			boost::bind(&session_impl::on_lsd_announce, this, _1));
-		TORRENT_ASSERT(!ec);
-
-#ifndef TORRENT_DISABLE_DHT
-		update_dht_announce_interval();
-#endif
-
-#ifndef TORRENT_DISABLE_LOGGING
-		session_log(" done starting session");
-#endif
-	}
-
 	void session_impl::save_state(entry* eptr, boost::uint32_t flags) const
 	{
 		TORRENT_ASSERT(is_single_thread());
@@ -1075,6 +1075,9 @@ namespace aux {
 		// has an internal counter and won't release the network
 		// thread until they're all dead (via m_work).
 		m_disk_thread.set_num_threads(0, false);
+
+		// now it's OK for the network thread to exit
+		m_work.reset();
 	}
 
 	bool session_impl::has_connection(peer_connection* p) const
@@ -3988,88 +3991,6 @@ retry:
 		m_delayed_uncorks.clear();
 	}
 
-#if defined _MSC_VER && defined TORRENT_DEBUG
-	static void straight_to_debugger(unsigned int, _EXCEPTION_POINTERS*)
-	{ throw; }
-#endif
-
-	void session_impl::main_thread()
-	{
-#if defined _MSC_VER && defined TORRENT_DEBUG
-		// workaround for microsofts
-		// hardware exceptions that makes
-		// it hard to debug stuff
-		::_set_se_translator(straight_to_debugger);
-#endif
-		// this is a debug facility
-		// see single_threaded in debug.hpp
-		thread_started();
-
-		TORRENT_ASSERT(is_single_thread());
-
-		// initialize async operations
-		init();
-
-		bool stop_loop = false;
-		while (!stop_loop)
-		{
-			error_code ec;
-			m_io_service.run(ec);
-			if (ec)
-			{
-#ifdef TORRENT_DEBUG
-				fprintf(stderr, "%s\n", ec.message().c_str());
-				std::string err = ec.message();
-#endif
-				TORRENT_ASSERT(false);
-			}
-			m_io_service.reset();
-
-			stop_loop = m_abort;
-		}
-
-#ifndef TORRENT_DISABLE_LOGGING
-		session_log(" locking mutex");
-#endif
-
-/*
-#ifdef TORRENT_DEBUG
-		for (torrent_map::iterator i = m_torrents.begin();
-			i != m_torrents.end(); ++i)
-		{
-			TORRENT_ASSERT(i->second->num_peers() == 0);
-		}
-#endif
-*/
-#ifndef TORRENT_DISABLE_LOGGING
-		session_log(" cleaning up torrents");
-#endif
-
-		// clear the torrent LRU (probably not strictly necessary)
-		list_node* i = m_torrent_lru.get_all();
-#if TORRENT_USE_ASSERTS
-		// clear the prev and next pointers in all torrents
-		// to avoid the assert when destructing them
-		while (i)
-		{
-			list_node* tmp = i;
-			i = i->next;
-			tmp->next = NULL;
-			tmp->prev= NULL;
-		}
-#else
-		TORRENT_UNUSED(i);
-#endif
-		m_torrents.clear();
-
-		TORRENT_ASSERT(m_torrents.empty());
-		TORRENT_ASSERT(m_connections.empty());
-
-#if TORRENT_USE_ASSERTS && defined BOOST_HAS_PTHREADS
-		m_network_thread = 0;
-#endif
-	}
-
 	boost::shared_ptr<torrent> session_impl::delay_load_torrent(sha1_hash const& info_hash
 		, peer_connection* pc)
 	{
@@ -5623,11 +5544,6 @@ retry:
 		// this is not allowed to be the network thread!
 		TORRENT_ASSERT(is_not_thread());
 
-		m_io_service.post(boost::bind(&session_impl::abort, this));
-
-		// now it's OK for the network thread to exit
-		m_work.reset();
-
 #if defined TORRENT_ASIO_DEBUGGING
 		int counter = 0;
 		while (log_async())
@@ -5640,12 +5556,8 @@ retry:
 		async_dec_threads();
 
 		fprintf(stderr, "\n\nEXPECTS NO MORE ASYNC OPS\n\n\n");
-
-//		m_io_service.post(boost::bind(&io_service::stop, &m_io_service));
 #endif
 
-		if (m_thread) m_thread->join();
-
 		m_udp_socket.unsubscribe(this);
 		m_udp_socket.unsubscribe(&m_utp_socket_manager);
 		m_udp_socket.unsubscribe(&m_tracker_manager);
@@ -5684,6 +5596,22 @@ retry:
 			fclose(f);
 		}
 #endif
+
+		// clear the torrent LRU. We do this to avoid having the torrent
+		// destructor assert because it's still linked into the lru list
+#if TORRENT_USE_ASSERTS
+		list_node* i = m_torrent_lru.get_all();
+		// clear the prev and next pointers in all torrents
+		// to avoid the assert when destructing them
+		while (i)
+		{
+			list_node* tmp = i;
+			i = i->next;
+			tmp->next = NULL;
+			tmp->prev = NULL;
+		}
+#endif
+
 	}
 
 #ifndef TORRENT_NO_DEPRECATE
@@ -5944,9 +5872,6 @@ retry:
 		m_pending_auto_manage = true;
 		m_need_auto_manage = true;
 
-		// if we haven't started yet, don't actually trigger this
-		if (!m_thread) return;
-
 		m_io_service.post(boost::bind(&session_impl::on_trigger_auto_manage, this));
 	}
 
@@ -5998,15 +5923,6 @@ retry:
 
 		m_dht_interval_update_torrents = m_torrents.size();
 
-		// if we haven't started yet, don't actually trigger this
-		if (!m_thread)
-		{
-#ifndef TORRENT_DISABLE_LOGGING
-			session_log("not starting DHT announce timer: thread not running yet");
-#endif
-			return;
-		}
-
 		if (m_abort)
 		{
 #ifndef TORRENT_DISABLE_LOGGING
@@ -6044,9 +5960,6 @@ retry:
 
 		if (!m_settings.get_bool(settings_pack::force_proxy)) return;
 
-		// if we haven't started yet, don't actually trigger this
-		if (!m_thread) return;
-
 		// enable force_proxy mode. We don't want to accept any incoming
 		// connections, except through a proxy.
 		stop_lsd();