eth/enode: simplify BufferIter

Signed-off-by: Csaba Kiraly <csaba.kiraly@gmail.com>

p2p/enode/iter.go

@@ -239,7 +239,7 @@ type BufferIter struct {
 	buffer    chan *Node
 	head      *Node
 	closed    chan struct{}
-	mu     sync.Mutex
+	closeOnce sync.Once
 }
 
 // NewBufferIter creates a new pre-fetch buffer of a given size.
@@ -267,35 +267,26 @@ func NewBufferIter(it Iterator, size int) Iterator {
 }
 
 func (b *BufferIter) Next() bool {
-	b.mu.Lock()
-	defer b.mu.Unlock()
-
 	select {
 	case b.head = <-b.buffer:
 	case <-b.closed:
-		return false
+		b.head = nil
 	}
 	return b.head != nil
 }
 
 func (b *BufferIter) Node() *Node {
-	b.mu.Lock()
-	defer b.mu.Unlock()
 	return b.head
 }
 
 func (b *BufferIter) Close() {
-	// Close the wrapped iterator first.
+	b.closeOnce.Do(func() {
 		b.it.Close()
 		close(b.closed)
-	// Wait for Next to terminate, then drain the buffer.
-	b.mu.Lock()
-	defer b.mu.Unlock()
+		// Wait for Next to terminate.
 		for range b.buffer {
 		}
-	b.buffer = nil
-	b.head = nil
-	b.it = nil
+	})
 }
 
 // FairMix aggregates multiple node iterators. The mixer itself is an iterator which ends