mempool: p2p refactor (#5919)

libs/sync/sync.go

@@ -13,3 +13,31 @@ type Mutex struct {
 type RWMutex struct {
 	sync.RWMutex
 }
+
+// Closer implements a primitive to close a channel that signals process
+// termination while allowing a caller to call Close multiple times safely. It
+// should be used in cases where guarantees cannot be made about when and how
+// many times closure is executed.
+type Closer struct {
+	closeOnce sync.Once
+	doneCh    chan struct{}
+}
+
+// NewCloser returns a reference to a new Closer.
+func NewCloser() *Closer {
+	return &Closer{doneCh: make(chan struct{})}
+}
+
+// Done returns the internal done channel allowing the caller either block or wait
+// for the Closer to be terminated/closed.
+func (c *Closer) Done() <-chan struct{} {
+	return c.doneCh
+}
+
+// Close gracefully closes the Closer. A caller should only call Close once, but
+// it is safe to call it successive times.
+func (c *Closer) Close() {
+	c.closeOnce.Do(func() {
+		close(c.doneCh)
+	})
+}