pool: pre-update seenAlready atomically so there is no risk of the same event being parsed and dispatched twice racily.

pool.go

@@ -329,12 +329,15 @@ func (pool *SimplePool) FetchManyReplaceable(
 
 	seenAlreadyLatest := xsync.NewMapOf[ReplaceableKey, Timestamp]()
 	opts = append(opts, WithCheckDuplicateReplaceable(func(rk ReplaceableKey, ts Timestamp) bool {
-		latest, _ := seenAlreadyLatest.Load(rk)
+		updated := false
+		seenAlreadyLatest.Compute(rk, func(latest Timestamp, _ bool) (newValue Timestamp, delete bool) {
 			if ts > latest {
-			seenAlreadyLatest.Store(rk, ts)
-			return false // just stored the most recent
+				updated = true // we are updating the most recent
+				return ts, false
 			}
-		return true // already had one that was more recent
+			return latest, false // the one we had was already more recent
+		})
+		return updated
 	}))
 
 	for _, url := range urls {
@@ -538,8 +541,6 @@ func (pool *SimplePool) subMany(
 							mh(ie)
 						}
 
-						seenAlready.Store(evt.ID, evt.CreatedAt)
-
 						select {
 						case events <- ie:
 						case <-ctx.Done():
@@ -593,14 +594,16 @@ func (pool *SimplePool) SubManyEose(
 	filters Filters,
 	opts ...SubscriptionOption,
 ) chan RelayEvent {
-	seenAlready := xsync.NewMapOf[string, bool]()
-	return pool.subManyEoseNonOverwriteCheckDuplicate(ctx, urls, filters, WithCheckDuplicate(func(id, relay string) bool {
-		_, exists := seenAlready.Load(id)
+	seenAlready := xsync.NewMapOf[string, struct{}]()
+	return pool.subManyEoseNonOverwriteCheckDuplicate(ctx, urls, filters,
+		WithCheckDuplicate(func(id, relay string) bool {
+			_, exists := seenAlready.LoadOrStore(id, struct{}{})
 			if exists && pool.duplicateMiddleware != nil {
 				pool.duplicateMiddleware(relay, id)
 			}
 			return exists
-	}), seenAlready, opts...)
+		}),
+		opts...)
 }
 
 func (pool *SimplePool) subManyEoseNonOverwriteCheckDuplicate(
@@ -608,7 +611,6 @@ func (pool *SimplePool) subManyEoseNonOverwriteCheckDuplicate(
 	urls []string,
 	filters Filters,
 	wcd WithCheckDuplicate,
-	seenAlready *xsync.MapOf[string, bool],
 	opts ...SubscriptionOption,
 ) chan RelayEvent {
 	ctx, cancel := context.WithCancelCause(ctx)
@@ -686,8 +688,6 @@ func (pool *SimplePool) subManyEoseNonOverwriteCheckDuplicate(
 						mh(ie)
 					}
 
-					seenAlready.Store(evt.ID, true)
-
 					select {
 					case events <- ie:
 					case <-ctx.Done():
@@ -759,7 +759,7 @@ func (pool *SimplePool) BatchedSubManyEose(
 	res := make(chan RelayEvent)
 	wg := sync.WaitGroup{}
 	wg.Add(len(dfs))
-	seenAlready := xsync.NewMapOf[string, bool]()
+	seenAlready := xsync.NewMapOf[string, struct{}]()
 
 	for _, df := range dfs {
 		go func(df DirectedFilter) {
@@ -767,12 +767,12 @@ func (pool *SimplePool) BatchedSubManyEose(
 				[]string{df.Relay},
 				Filters{df.Filter},
 				WithCheckDuplicate(func(id, relay string) bool {
-					_, exists := seenAlready.Load(id)
+					_, exists := seenAlready.LoadOrStore(id, struct{}{})
 					if exists && pool.duplicateMiddleware != nil {
 						pool.duplicateMiddleware(relay, id)
 					}
 					return exists
-				}), seenAlready, opts...,
+				}), opts...,
 			) {
 				select {
 				case res <- ie: