use a named lock instead of a single per-pool mutex.

pool.go

@@ -13,7 +13,6 @@ type SimplePool struct {
 	Relays  map[string]*Relay
 	Context context.Context
 
-	mutex  sync.Mutex
 	cancel context.CancelFunc
 }
 
@@ -31,8 +30,7 @@ func NewSimplePool(ctx context.Context) *SimplePool {
 func (pool *SimplePool) EnsureRelay(url string) (*Relay, error) {
 	nm := NormalizeURL(url)
 
-	pool.mutex.Lock()
+	defer namedLock(url)()
-	defer pool.mutex.Unlock()
 
 	relay, ok := pool.Relays[nm]
 	if ok && relay.IsConnected() {

utils.go

@@ -3,10 +3,22 @@ package nostr
 import (
 	"net/url"
 	"strings"
+	"sync"
 
+	"github.com/dgraph-io/ristretto/z"
 	"golang.org/x/exp/constraints"
 )
 
+const MAX_LOCKS = 50
+
+var namedMutexPool = make([]sync.Mutex, MAX_LOCKS)
+
+func namedLock(name string) (unlock func()) {
+	idx := z.MemHashString(name) % MAX_LOCKS
+	namedMutexPool[idx].Lock()
+	return namedMutexPool[idx].Unlock
+}
+
 func similar[E constraints.Ordered](as, bs []E) bool {
 	if len(as) != len(bs) {
 		return false