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/utils/rand.go

@@ -0,0 +1,46 @@
+// 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 utils
+
+import (
+	"math/rand"
+	"sync"
+)
+
+// lockedSource allows a random number generator to be used by multiple goroutines concurrently.
+// The code is very similar to math/rand.lockedSource, which is unfortunately not exposed.
+type lockedSource struct {
+	mut sync.Mutex
+	src rand.Source
+}
+
+// NewRand returns a rand.Rand that is threadsafe.
+func NewRand(seed int64) *rand.Rand {
+	return rand.New(&lockedSource{src: rand.NewSource(seed)})
+}
+
+func (r *lockedSource) Int63() (n int64) {
+	r.mut.Lock()
+	n = r.src.Int63()
+	r.mut.Unlock()
+	return
+}
+
+// Seed implements Seed() of Source
+func (r *lockedSource) Seed(seed int64) {
+	r.mut.Lock()
+	r.src.Seed(seed)
+	r.mut.Unlock()
+}