Terminate running background transform on exit

Close #4422

src/util/concurrent_set.go

@@ -0,0 +1,39 @@
+package util
+
+import "sync"
+
+// ConcurrentSet is a thread-safe set implementation.
+type ConcurrentSet[T comparable] struct {
+	lock  sync.RWMutex
+	items map[T]struct{}
+}
+
+// NewConcurrentSet creates a new ConcurrentSet.
+func NewConcurrentSet[T comparable]() *ConcurrentSet[T] {
+	return &ConcurrentSet[T]{
+		items: make(map[T]struct{}),
+	}
+}
+
+// Add adds an item to the set.
+func (s *ConcurrentSet[T]) Add(item T) {
+	s.lock.Lock()
+	defer s.lock.Unlock()
+	s.items[item] = struct{}{}
+}
+
+// Remove removes an item from the set.
+func (s *ConcurrentSet[T]) Remove(item T) {
+	s.lock.Lock()
+	defer s.lock.Unlock()
+	delete(s.items, item)
+}
+
+// ForEach iterates over each item in the set and applies the provided function.
+func (s *ConcurrentSet[T]) ForEach(fn func(item T)) {
+	s.lock.RLock()
+	defer s.lock.RUnlock()
+	for item := range s.items {
+		fn(item)
+	}
+}