swarm: integrate OpenTracing; propagate ctx to internal APIs (#17169)

* swarm: propagate ctx, enable opentracing

* swarm/tracing: log error when tracing is misconfigured

vendor/github.com/uber/jaeger-client-go/rpcmetrics/endpoints.go

@@ -0,0 +1,63 @@
+// Copyright (c) 2017 Uber Technologies, Inc.
+//
+// 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 rpcmetrics
+
+import "sync"
+
+// normalizedEndpoints is a cache for endpointName -> safeName mappings.
+type normalizedEndpoints struct {
+	names       map[string]string
+	maxSize     int
+	defaultName string
+	normalizer  NameNormalizer
+	mux         sync.RWMutex
+}
+
+func newNormalizedEndpoints(maxSize int, normalizer NameNormalizer) *normalizedEndpoints {
+	return &normalizedEndpoints{
+		maxSize:    maxSize,
+		normalizer: normalizer,
+		names:      make(map[string]string, maxSize),
+	}
+}
+
+// normalize looks up the name in the cache, if not found it uses normalizer
+// to convert the name to a safe name. If called with more than maxSize unique
+// names it returns "" for all other names beyond those already cached.
+func (n *normalizedEndpoints) normalize(name string) string {
+	n.mux.RLock()
+	norm, ok := n.names[name]
+	l := len(n.names)
+	n.mux.RUnlock()
+	if ok {
+		return norm
+	}
+	if l >= n.maxSize {
+		return ""
+	}
+	return n.normalizeWithLock(name)
+}
+
+func (n *normalizedEndpoints) normalizeWithLock(name string) string {
+	norm := n.normalizer.Normalize(name)
+	n.mux.Lock()
+	defer n.mux.Unlock()
+	// cache may have grown while we were not holding the lock
+	if len(n.names) >= n.maxSize {
+		return ""
+	}
+	n.names[name] = norm
+	return norm
+}