make performance counters able to blend in values, reducing a peer_connection -> session dependency on a sliding average state (this can be used for disk stats too)

include/libtorrent/aux_/session_impl.hpp

@@ -409,12 +409,6 @@ namespace libtorrent
 			void set_port_filter(port_filter const& f);
 			port_filter const& get_port_filter() const;
 
-			void request_latency_sample(int us)
-			{
-				m_request_latency.add_sample(us);
-				m_stats_counters.set_value(counters::request_latency, m_request_latency.mean());
-			}
-
 			// TODO: move the login info into the tracker_request object
 			void queue_tracker_request(tracker_request& req
 				, std::string login, boost::weak_ptr<request_callback> c
@@ -1224,10 +1218,6 @@ namespace libtorrent
 
 			counters m_stats_counters;
 
-			// the sliding average of the latency (in microseconds) from an
-			// incoming request to sending the data back over the socket
-			sliding_average<50> m_request_latency;
-
 #ifdef TORRENT_UPNP_LOGGING
 			std::ofstream m_upnp_log;
 #endif

include/libtorrent/aux_/session_interface.hpp

@@ -241,8 +241,6 @@ namespace libtorrent { namespace aux
 
 		virtual int peak_up_rate() const = 0;
 
-		virtual void request_latency_sample(int us) = 0;
-
 		enum torrent_list_index
 		{
 			// this is the set of (subscribed) torrents that have changed

include/libtorrent/performance_counters.hpp

@@ -388,6 +388,7 @@ namespace libtorrent
 		boost::int64_t operator[](int i) const;
 
 		void set_value(int c, boost::int64_t value);
+		void blend_stats_counter(int c, boost::int64_t value, int ratio);
 
 	private:
 

src/peer_connection.cpp

@@ -5189,10 +5189,7 @@ namespace libtorrent
 			, r.piece, r.start, r.length);
 #endif
 
-		// TODO: 3 it would be nice if the sliding_average state required
-		// for this would be baked into the counters object, in which case this
-		// would not be a session_impl dependency.
-		m_ses.request_latency_sample(disk_rtt);
+		m_counters.blend_stats_counter(counters::request_latency, disk_rtt, 5);
 
 		// we probably just pulled this piece into the cache.
 		// if it's rare enough to make it into the suggested piece

src/performance_counters.cpp

@@ -71,6 +71,22 @@ namespace libtorrent {
 		return m_stats_counter[c] += value;
 	}
 
+	// ratio is a vaue between 0 and 100 representing the percentage the value
+	// is blended in at.
+	void counters::blend_stats_counter(int c, boost::int64_t value, int ratio)
+	{
+		TORRENT_ASSERT(c >= 0);
+		TORRENT_ASSERT(c < num_counters);
+		TORRENT_ASSERT(ratio >= 0);
+		TORRENT_ASSERT(ratio <= 100);
+
+		TORRENT_ASSERT(num_stats_counters);
+
+		// TODO: 2 to make this thread safe, use compare_exchange_weak
+		boost::uint64_t current = m_stats_counter[c];
+		m_stats_counter[c] = (current * (100-ratio) + value * ratio) / 100;
+	}
+
 	void counters::set_value(int c, boost::int64_t value)
 	{
 		TORRENT_ASSERT(c >= 0);

src/session_stats.cpp

@@ -38,6 +38,8 @@ POSSIBILITY OF SUCH DAMAGE.
 namespace libtorrent
 {
 
+	// TODO: 3 this function could just use the static metrics array
+	// instead of taking it as an argument. Also, document it
 	int find_metric_idx(std::vector<stats_metric> const& metrics
 		, char const* name)
 	{
@@ -48,6 +50,9 @@ namespace libtorrent
 		return i->value_index;
 	}
 
+	// TODO: 3 the type of counter does not need to be stored in this array.
+	// when the user asks for the list of counters, that field could be
+	// generated based on the range of the counter index.
 #define METRIC(category, name, type) { #category "." #name, counters:: name, stats_metric:: type},
 	const static stats_metric metrics[] =
 	{