add comments

balancer.go

@@ -7,8 +7,9 @@ import (
 	"google.golang.org/grpc/transport"
 )
 
+// Address represents a server the client connects to.
 type Address struct {
-	// Addr is the peer address on which a connection will be established.
+	// Addr is the server address on which a connection will be established.
 	Addr string
 	// Metadata is the information associated with Addr, which may be used
 	// to make load balancing decision. This is from the metadata attached
@@ -32,18 +33,20 @@ type Balancer interface {
 	Close() error
 }
 
+// RoundRobin returns a Balancer that selects addresses round-robin.
 func RoundRobin() Balancer {
 	return &roundRobin{}
 }
 
 type roundRobin struct {
-	mu      sync.Mutex
-	addrs   []Address
-	next    int
-	waitCh  chan struct{}
-	pending int
+	mu     sync.Mutex
+	addrs  []Address
+	next   int // index of the next address to return for Get()
+	waitCh chan struct{}
 }
 
+// Up appends addr to the end of rr.addrs and sends notification if there
+// are pending Get() calls.
 func (rr *roundRobin) Up(addr Address) func(error) {
 	rr.mu.Lock()
 	defer rr.mu.Unlock()
@@ -64,6 +67,7 @@ func (rr *roundRobin) Up(addr Address) func(error) {
 	}
 }
 
+// down removes addr from rr.addrs and moves the remaining addrs forward.
 func (rr *roundRobin) down(addr Address, err error) {
 	rr.mu.Lock()
 	defer rr.mu.Unlock()
@@ -76,6 +80,7 @@ func (rr *roundRobin) down(addr Address, err error) {
 	}
 }
 
+// Get returns the next addr in the rotation. It blocks if there is no address available.
 func (rr *roundRobin) Get(ctx context.Context) (addr Address, put func(), err error) {
 	var ch chan struct{}
 	rr.mu.Lock()
@@ -85,13 +90,13 @@ func (rr *roundRobin) Get(ctx context.Context) (addr Address, put func(), err er
 	if len(rr.addrs) > 0 {
 		addr = rr.addrs[rr.next]
 		rr.next++
-		rr.pending++
 		rr.mu.Unlock()
 		put = func() {
 			rr.put(ctx, addr)
 		}
 		return
 	}
+	// There is no address available. Wait on rr.waitCh.
 	if rr.waitCh == nil {
 		ch = make(chan struct{})
 		rr.waitCh = ch
@@ -116,7 +121,6 @@ func (rr *roundRobin) Get(ctx context.Context) (addr Address, put func(), err er
 			}
 			addr = rr.addrs[rr.next]
 			rr.next++
-			rr.pending++
 			rr.mu.Unlock()
 			put = func() {
 				rr.put(ctx, addr)
@@ -127,9 +131,6 @@ func (rr *roundRobin) Get(ctx context.Context) (addr Address, put func(), err er
 }
 
 func (rr *roundRobin) put(ctx context.Context, addr Address) {
-	rr.mu.Lock()
-	defer rr.mu.Unlock()
-	rr.pending--
 }
 
 func (rr *roundRobin) Close() error {

clientconn.go

@@ -618,7 +618,7 @@ func (ac *addrConn) resetTransport(closeTransport bool) error {
 			closeTransport = false
 			select {
 			case <-time.After(sleepTime):
-			case <-cc.shutdownChan:
+			case <-ac.shutdownChan:
 			}
 			retries++
 			grpclog.Printf("grpc: addrConn.resetTransport failed to create client transport: %v; Reconnecting to %q", err, ac.addr)