Initial

Signed-off-by: Alex Ellis (OpenFaaS Ltd) <alexellis2@gmail.com>

vendor/google.golang.org/grpc/balancer/roundrobin/roundrobin.go

@@ -0,0 +1,83 @@
+/*
+ *
+ * Copyright 2017 gRPC authors.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ *
+ */
+
+// Package roundrobin defines a roundrobin balancer. Roundrobin balancer is
+// installed as one of the default balancers in gRPC, users don't need to
+// explicitly install this balancer.
+package roundrobin
+
+import (
+	"context"
+	"sync"
+
+	"google.golang.org/grpc/balancer"
+	"google.golang.org/grpc/balancer/base"
+	"google.golang.org/grpc/grpclog"
+	"google.golang.org/grpc/internal/grpcrand"
+	"google.golang.org/grpc/resolver"
+)
+
+// Name is the name of round_robin balancer.
+const Name = "round_robin"
+
+// newBuilder creates a new roundrobin balancer builder.
+func newBuilder() balancer.Builder {
+	return base.NewBalancerBuilderWithConfig(Name, &rrPickerBuilder{}, base.Config{HealthCheck: true})
+}
+
+func init() {
+	balancer.Register(newBuilder())
+}
+
+type rrPickerBuilder struct{}
+
+func (*rrPickerBuilder) Build(readySCs map[resolver.Address]balancer.SubConn) balancer.Picker {
+	grpclog.Infof("roundrobinPicker: newPicker called with readySCs: %v", readySCs)
+	if len(readySCs) == 0 {
+		return base.NewErrPicker(balancer.ErrNoSubConnAvailable)
+	}
+	var scs []balancer.SubConn
+	for _, sc := range readySCs {
+		scs = append(scs, sc)
+	}
+	return &rrPicker{
+		subConns: scs,
+		// Start at a random index, as the same RR balancer rebuilds a new
+		// picker when SubConn states change, and we don't want to apply excess
+		// load to the first server in the list.
+		next: grpcrand.Intn(len(scs)),
+	}
+}
+
+type rrPicker struct {
+	// subConns is the snapshot of the roundrobin balancer when this picker was
+	// created. The slice is immutable. Each Get() will do a round robin
+	// selection from it and return the selected SubConn.
+	subConns []balancer.SubConn
+
+	mu   sync.Mutex
+	next int
+}
+
+func (p *rrPicker) Pick(ctx context.Context, opts balancer.PickOptions) (balancer.SubConn, func(balancer.DoneInfo), error) {
+	p.mu.Lock()
+	sc := p.subConns[p.next]
+	p.next = (p.next + 1) % len(p.subConns)
+	p.mu.Unlock()
+	return sc, nil, nil
+}