code review 4079053: replace non-blocking send, receive syntax with select

src/pkg/rpc/client.go

Index: src/pkg/rpc/client.go
===================================================================
--- a/src/pkg/rpc/client.go
+++ b/src/pkg/rpc/client.go
@@ -58,7 +58,7 @@
 	if client.shutdown != nil {
 		c.Error = client.shutdown
 		client.mutex.Unlock()
-		_ = c.Done <- c // do not block
+		c.done()
 		return
 	}
 	c.seq = client.seq
@@ -102,16 +102,14 @@
 			// Empty strings should turn into nil os.Errors
 			c.Error = nil
 		}
-		// We don't want to block here.  It is the caller's responsibility to make
-		// sure the channel has enough buffer space. See comment in Go().
-		_ = c.Done <- c // do not block
+		c.done()
 	}
 	// Terminate pending calls.
 	client.mutex.Lock()
 	client.shutdown = err
 	for _, call := range client.pending {
 		call.Error = err
-		_ = call.Done <- call // do not block
+		call.done()
 	}
 	client.mutex.Unlock()
 	if err != os.EOF || !client.closing {
@@ -119,6 +117,16 @@
 	}
 }
 
+func (call *Call) done() {
+	select {
+	case call.Done <- call:
+		// ok
+	default:
+		// We don't want to block here.  It is the caller's responsibility to make
+		// sure the channel has enough buffer space. See comment in Go().
+	}
+}
+
 // NewClient returns a new Client to handle requests to the
 // set of services at the other end of the connection.
 func NewClient(conn io.ReadWriteCloser) *Client {
@@ -233,7 +241,7 @@
 	c.Done = done
 	if client.shutdown != nil {
 		c.Error = client.shutdown
-		_ = c.Done <- c // do not block
+		c.done()
 		return c
 	}
 	client.send(c)