try grpc lb interface

rpcx/internal/balancer/roundrobin/roundrobin.go

@@ -0,0 +1,64 @@
+package roundrobin
+
+import (
+	"context"
+	"fmt"
+	"math/rand"
+	"sync"
+	"time"
+
+	"google.golang.org/grpc/balancer"
+	"google.golang.org/grpc/balancer/base"
+	"google.golang.org/grpc/resolver"
+)
+
+const Name = "zero_rr"
+
+func init() {
+	balancer.Register(newRoundRobinBuilder())
+}
+
+type roundRobinPickerBuilder struct {
+}
+
+func newRoundRobinBuilder() balancer.Builder {
+	return base.NewBalancerBuilder(Name, new(roundRobinPickerBuilder))
+}
+
+func (b *roundRobinPickerBuilder) Build(readySCs map[resolver.Address]balancer.SubConn) balancer.Picker {
+	rand.Seed(time.Now().UnixNano())
+	picker := &roundRobinPicker{
+		index: rand.Int(),
+	}
+
+	for addr, conn := range readySCs {
+		picker.conns = append(picker.conns, &subConn{
+			addr: addr,
+			conn: conn,
+		})
+	}
+
+	return picker
+}
+
+type roundRobinPicker struct {
+	conns []*subConn
+	index int
+	lock  sync.Mutex
+}
+
+func (p *roundRobinPicker) Pick(ctx context.Context, info balancer.PickInfo) (
+	conn balancer.SubConn, done func(balancer.DoneInfo), err error) {
+	fmt.Println(p.conns)
+	p.lock.Lock()
+	defer p.lock.Unlock()
+
+	p.index = (p.index + 1) % len(p.conns)
+	return p.conns[p.index].conn, func(info balancer.DoneInfo) {
+	}, nil
+}
+
+type subConn struct {
+	addr resolver.Address
+	conn balancer.SubConn
+}