bitswap: preallocate peers array on bitswap stat

Avoids lots of reallocations under a lock.

License: MIT
Signed-off-by: Steven Allen <steven@stebalien.com>

exchange/bitswap/decision/engine.go

@@ -201,7 +201,8 @@ func (e *Engine) Peers() []peer.ID {
 	e.lock.Lock()
 	defer e.lock.Unlock()
 
-	response := make([]peer.ID, 0)
+	response := make([]peer.ID, 0, len(e.ledgerMap))
+
 	for _, ledger := range e.ledgerMap {
 		response = append(response, ledger.Partner)
 	}

exchange/bitswap/stat.go

@@ -32,7 +32,10 @@ func (bs *Bitswap) Stat() (*Stat, error) {
 	st.DataReceived = c.dataRecvd
 	bs.counterLk.Unlock()
 
-	for _, p := range bs.engine.Peers() {
+	peers := bs.engine.Peers()
+	st.Peers = make([]string, 0, len(peers))
+
+	for _, p := range peers {
 		st.Peers = append(st.Peers, p.Pretty())
 	}
 	sort.Strings(st.Peers)