fundign: use atomic.Uint64 for chanIDNonce

This lets us get rid of the mutex usage there. We also shift the algo slightly to increment by 1, then use that as the next value, which plays nicer with the atomics.

Author: Roasbeef

funding/manager.go

@@ -6,6 +6,7 @@ import (
 	"fmt"
 	"io"
 	"sync"
+	"sync/atomic"
 	"time"
 
 	"github.com/btcsuite/btcd/blockchain"
@@ -561,10 +562,11 @@ type Manager struct {
 	// temporary channel ID's.
 	chanIDKey [32]byte
 
+	nonceMtx sync.RWMutex
+
 	// chanIDNonce is a nonce that's incremented for each new funding
 	// reservation created.
-	nonceMtx    sync.RWMutex
-	chanIDNonce uint64
+	chanIDNonce atomic.Uint64
 
 	// pendingMusigNonces is used to store the musig2 nonce we generate to
 	// send funding locked until we receive a funding locked message from
@@ -802,19 +804,20 @@ type PendingChanID = [32]byte
 func (f *Manager) nextPendingChanID() PendingChanID {
 	// Obtain a fresh nonce. We do this by encoding the current nonce
 	// counter, then incrementing it by one.
-	f.nonceMtx.Lock()
-	var nonce [8]byte
-	binary.LittleEndian.PutUint64(nonce[:], f.chanIDNonce)
-	f.chanIDNonce++
-	f.nonceMtx.Unlock()
+	nextNonce := f.chanIDNonce.Add(1)
+
+	var nonceBytes [8]byte
+	binary.LittleEndian.PutUint64(nonceBytes[:], nextNonce)
 
 	// We'll generate the next pending channelID by "encrypting" 32-bytes
 	// of zeroes which'll extract 32 random bytes from our stream cipher.
 	var (
 		nextChanID PendingChanID
 		zeroes     [32]byte
 	)
-	salsa20.XORKeyStream(nextChanID[:], zeroes[:], nonce[:], &f.chanIDKey)
+	salsa20.XORKeyStream(
+		nextChanID[:], zeroes[:], nonceBytes[:], &f.chanIDKey,
+	)
 
 	return nextChanID
 }