add metric producer manager. (#1039)

* add metric producer manager.

* added immutable test and removed contains method.

* fix fmt and lint.

* fix immutability.

* add nil check and fix test.

* fix review comment.

metric/producer/manager.go

@@ -0,0 +1,89 @@
+// Copyright 2019, OpenCensus 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 producer
+
+import (
+	"sync"
+)
+
+type manager struct {
+	mu        sync.RWMutex
+	producers map[Producer]struct{}
+}
+
+var prodMgr *manager
+var once sync.Once
+
+func getManager() *manager {
+	once.Do(func() {
+		prodMgr = &manager{}
+		prodMgr.producers = make(map[Producer]struct{})
+	})
+	return prodMgr
+}
+
+// Add adds the producer to the manager if it is not already present.
+// The manager maintains the list of active producers. It provides
+// this list to a reader to read metrics from each producer and then export.
+func Add(producer Producer) {
+	if producer == nil {
+		return
+	}
+	pm := getManager()
+	pm.add(producer)
+}
+
+// Delete deletes the producer from the manager if it is present.
+func Delete(producer Producer) {
+	if producer == nil {
+		return
+	}
+	pm := getManager()
+	pm.delete(producer)
+}
+
+// GetAll returns a slice of all producer currently registered with
+// the manager. For each call it generates a new slice. The slice
+// should not be cached as registration may change at any time. It is
+// typically called periodically by exporter to read metrics from
+// the producers.
+func GetAll() []Producer {
+	pm := getManager()
+	return pm.getAll()
+}
+
+func (pm *manager) getAll() []Producer {
+	pm.mu.Lock()
+	defer pm.mu.Unlock()
+	producers := make([]Producer, len(pm.producers))
+	i := 0
+	for producer := range pm.producers {
+		producers[i] = producer
+		i++
+	}
+	return producers
+}
+
+func (pm *manager) add(producer Producer) {
+	pm.mu.Lock()
+	defer pm.mu.Unlock()
+	pm.producers[producer] = struct{}{}
+}
+
+func (pm *manager) delete(producer Producer) {
+	pm.mu.Lock()
+	defer pm.mu.Unlock()
+	delete(pm.producers, producer)
+}

metric/producer/manager_test.go

@@ -0,0 +1,147 @@
+// Copyright 2019, OpenCensus 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 producer
+
+import (
+	"testing"
+
+	"go.opencensus.io/metric/metricdata"
+)
+
+type testProducer struct {
+	name string
+}
+
+var (
+	myProd1 = newTestProducer("foo")
+	myProd2 = newTestProducer("bar")
+	myProd3 = newTestProducer("foobar")
+)
+
+func newTestProducer(name string) *testProducer {
+	return &testProducer{name}
+}
+
+func (mp *testProducer) Read() []*metricdata.Metric {
+	return nil
+}
+
+func TestAdd(t *testing.T) {
+	Add(myProd1)
+	Add(myProd2)
+
+	got := GetAll()
+	want := []*testProducer{myProd1, myProd2}
+	checkSlice(got, want, t)
+	deleteAll()
+}
+
+func TestAddExisting(t *testing.T) {
+	Add(myProd1)
+	Add(myProd2)
+	Add(myProd1)
+
+	got := GetAll()
+	want := []*testProducer{myProd2, myProd1}
+	checkSlice(got, want, t)
+	deleteAll()
+}
+
+func TestAddNil(t *testing.T) {
+	Add(nil)
+
+	got := GetAll()
+	want := []*testProducer{}
+	checkSlice(got, want, t)
+	deleteAll()
+}
+
+func TestDelete(t *testing.T) {
+	Add(myProd1)
+	Add(myProd2)
+	Add(myProd3)
+	Delete(myProd2)
+
+	got := GetAll()
+	want := []*testProducer{myProd1, myProd3}
+	checkSlice(got, want, t)
+	deleteAll()
+}
+
+func TestDeleteNonExisting(t *testing.T) {
+	Add(myProd1)
+	Add(myProd3)
+	Delete(myProd2)
+
+	got := GetAll()
+	want := []*testProducer{myProd1, myProd3}
+	checkSlice(got, want, t)
+	deleteAll()
+}
+
+func TestDeleteNil(t *testing.T) {
+	Add(myProd1)
+	Add(myProd3)
+	Delete(nil)
+
+	got := GetAll()
+	want := []*testProducer{myProd1, myProd3}
+	checkSlice(got, want, t)
+	deleteAll()
+}
+
+func TestGetAllNil(t *testing.T) {
+	got := GetAll()
+	want := []*testProducer{}
+	checkSlice(got, want, t)
+	deleteAll()
+}
+
+func TestImmutableProducerList(t *testing.T) {
+	Add(myProd1)
+	Add(myProd2)
+
+	producersToMutate := GetAll()
+	producersToMutate[0] = myProd3
+	got := GetAll()
+	want := []*testProducer{myProd1, myProd2}
+	checkSlice(got, want, t)
+	deleteAll()
+}
+
+func checkSlice(got []Producer, want []*testProducer, t *testing.T) {
+	gotLen := len(got)
+	wantLen := len(want)
+	if gotLen != wantLen {
+		t.Errorf("got len: %d want: %d\n", gotLen, wantLen)
+	} else {
+		gotMap := map[Producer]struct{}{}
+		for i := 0; i < gotLen; i++ {
+			gotMap[got[i]] = struct{}{}
+		}
+		for i := 0; i < wantLen; i++ {
+			delete(gotMap, want[i])
+		}
+		if len(gotMap) > 0 {
+			t.Errorf("got %v, want %v\n", got, want)
+		}
+	}
+}
+
+func deleteAll() {
+	Delete(myProd1)
+	Delete(myProd2)
+	Delete(myProd3)
+}

metric/metricexport/producer.go → metric/producer/producer.go

@@ -1,4 +1,4 @@
-// Copyright 2018, OpenCensus Authors
+// Copyright 2019, OpenCensus Authors
 //
 // Licensed under the Apache License, Version 2.0 (the "License");
 // you may not use this file except in compliance with the License.
@@ -12,7 +12,7 @@
 // See the License for the specific language governing permissions and
 // limitations under the License.
 
-package metricexport
+package producer
 
 import (
 	"go.opencensus.io/metric/metricdata"