Moves files

internal/backend/semaphore.go

@@ -0,0 +1,28 @@
+package backend
+
+import "restic/errors"
+
+// Semaphore limits access to a restricted resource.
+type Semaphore struct {
+	ch chan struct{}
+}
+
+// NewSemaphore returns a new semaphore with capacity n.
+func NewSemaphore(n uint) (*Semaphore, error) {
+	if n <= 0 {
+		return nil, errors.New("must be a positive number")
+	}
+	return &Semaphore{
+		ch: make(chan struct{}, n),
+	}, nil
+}
+
+// GetToken blocks until a Token is available.
+func (s *Semaphore) GetToken() {
+	s.ch <- struct{}{}
+}
+
+// ReleaseToken returns a token.
+func (s *Semaphore) ReleaseToken() {
+	<-s.ch
+}