Ensure 64-bit alignment of ConnStats fields

Fixes #262.

client.go

@@ -39,6 +39,9 @@ import (
 // Clients contain zero or more Torrents. A Client manages a blocklist, the
 // TCP/UDP protocol ports, and DHT as desired.
 type Client struct {
+	// An aggregate of stats over all connections. First in struct to ensure
+	// 64-bit alignment of fields. See #262.
+	stats  ConnStats
 	mu     sync.RWMutex
 	event  sync.Cond
 	closed missinggo.Event
@@ -62,8 +65,6 @@ type Client struct {
 	dopplegangerAddrs map[string]struct{}
 	badPeerIPs        map[string]struct{}
 	torrents          map[metainfo.Hash]*Torrent
-	// An aggregate of stats over all connections.
-	stats ConnStats
 
 	acceptLimiter map[ipStr]int
 }

connection.go

@@ -38,6 +38,9 @@ const (
 
 // Maintains the state of a connection with a peer.
 type connection struct {
+	// First to ensure 64-bit alignment for atomics. See #262.
+	stats ConnStats
+
 	t *Torrent
 	// The actual Conn, used for closing, and setting socket options.
 	conn     net.Conn
@@ -55,8 +58,6 @@ type connection struct {
 	// other ConnStat instances as determined when the *Torrent became known.
 	reconciledHandshakeStats bool
 
-	stats ConnStats
-
 	lastMessageReceived     time.Time
 	completedHandshake      time.Time
 	lastUsefulChunkReceived time.Time

torrent.go

@@ -45,6 +45,9 @@ type peersKey struct {
 
 // Maintains state of torrent within a Client.
 type Torrent struct {
+	// Torrent-level aggregate statistics. First in struct to ensure 64-bit
+	// alignment. See #262.
+	stats  ConnStats
 	cl     *Client
 	logger *log.Logger
 
@@ -134,8 +137,6 @@ type Torrent struct {
 	// These "inclinations" are used to give connections preference for
 	// different pieces.
 	connPieceInclinationPool sync.Pool
-	// Torrent-level statistics.
-	stats ConnStats
 
 	// Count of each request across active connections.
 	pendingRequests map[request]int