Update LRU usage (#1164)

This change updates the LRU cache implementation used in the trace
package, replacing github.com/hashicorp/golang-lru with
github.com/golang/groupcache, while preserving the manner in which trace
abstractions make use of the data structure.

The reason for this change is that github.com/hashicorp/golang-lru has a
Mozilla license, which is different from that of
github.com/census-instrumentation/opencensus-go. The difference (and the
mere presence of the former) makes it more difficult for open-source
projects (e.g., https://fuchsia.dev) to vendor the latter.

Author: joshuaseaton

go.mod

@@ -1,12 +1,14 @@
 module go.opencensus.io
 
 require (
+	github.com/golang/groupcache v0.0.0-20190702054246-869f871628b6
 	github.com/golang/protobuf v1.3.1
 	github.com/google/go-cmp v0.3.0
-	github.com/hashicorp/golang-lru v0.5.1
-	golang.org/x/net v0.0.0-20190501004415-9ce7a6920f09
+	golang.org/x/net v0.0.0-20190620200207-3b0461eec859
 	golang.org/x/sys v0.0.0-20190502145724-3ef323f4f1fd // indirect
 	golang.org/x/text v0.3.2 // indirect
 	google.golang.org/genproto v0.0.0-20190425155659-357c62f0e4bb // indirect
 	google.golang.org/grpc v1.20.1
 )
+
+go 1.13

go.sum

@@ -3,27 +3,28 @@ github.com/BurntSushi/toml v0.3.1/go.mod h1:xHWCNGjB5oqiDr8zfno3MHue2Ht5sIBksp03
 github.com/client9/misspell v0.3.4/go.mod h1:qj6jICC3Q7zFZvVWo7KLAzC3yx5G7kyvSDkc90ppPyw=
 github.com/golang/glog v0.0.0-20160126235308-23def4e6c14b h1:VKtxabqXZkF25pY9ekfRL6a582T4P37/31XEstQ5p58=
 github.com/golang/glog v0.0.0-20160126235308-23def4e6c14b/go.mod h1:SBH7ygxi8pfUlaOkMMuAQtPIUF8ecWP5IEl/CR7VP2Q=
+github.com/golang/groupcache v0.0.0-20190702054246-869f871628b6 h1:ZgQEtGgCBiWRM39fZuwSd1LwSqqSW0hOdXCYYDX0R3I=
+github.com/golang/groupcache v0.0.0-20190702054246-869f871628b6/go.mod h1:cIg4eruTrX1D+g88fzRXU5OdNfaM+9IcxsU14FzY7Hc=
 github.com/golang/mock v1.1.1/go.mod h1:oTYuIxOrZwtPieC+H1uAHpcLFnEyAGVDL/k47Jfbm0A=
 github.com/golang/protobuf v1.2.0 h1:P3YflyNX/ehuJFLhxviNdFxQPkGK5cDcApsge1SqnvM=
 github.com/golang/protobuf v1.2.0/go.mod h1:6lQm79b+lXiMfvg/cZm0SGofjICqVBUtrP5yJMmIC1U=
 github.com/golang/protobuf v1.3.1 h1:YF8+flBXS5eO826T4nzqPrxfhQThhXl0YzfuUPu4SBg=
 github.com/golang/protobuf v1.3.1/go.mod h1:6lQm79b+lXiMfvg/cZm0SGofjICqVBUtrP5yJMmIC1U=
 github.com/google/go-cmp v0.3.0 h1:crn/baboCvb5fXaQ0IJ1SGTsTVrWpDsCWC8EGETZijY=
 github.com/google/go-cmp v0.3.0/go.mod h1:8QqcDgzrUqlUb/G2PQTWiueGozuR1884gddMywk6iLU=
-github.com/hashicorp/golang-lru v0.5.1 h1:0hERBMJE1eitiLkihrMvRVBYAkpHzc/J3QdDN+dAcgU=
-github.com/hashicorp/golang-lru v0.5.1/go.mod h1:/m3WP610KZHVQ1SGc6re/UDhFvYD7pJ4Ao+sR/qLZy8=
 golang.org/x/crypto v0.0.0-20190308221718-c2843e01d9a2/go.mod h1:djNgcEr1/C05ACkg1iLfiJU5Ep61QUkGW8qpdssI0+w=
 golang.org/x/exp v0.0.0-20190121172915-509febef88a4/go.mod h1:CJ0aWSM057203Lf6IL+f9T1iT9GByDxfZKAQTCR3kQA=
 golang.org/x/lint v0.0.0-20181026193005-c67002cb31c3/go.mod h1:UVdnD1Gm6xHRNCYTkRU2/jEulfH38KcIWyp/GAMgvoE=
 golang.org/x/lint v0.0.0-20190227174305-5b3e6a55c961/go.mod h1:wehouNa3lNwaWXcvxsM5YxQ5yQlVC4a0KAMCusXpPoU=
+golang.org/x/lint v0.0.0-20190313153728-d0100b6bd8b3 h1:XQyxROzUlZH+WIQwySDgnISgOivlhjIEwaQaJEJrrN0=
 golang.org/x/lint v0.0.0-20190313153728-d0100b6bd8b3/go.mod h1:6SW0HCj/g11FgYtHlgUYUwCkIfeOF89ocIRzGO/8vkc=
 golang.org/x/net v0.0.0-20180724234803-3673e40ba225/go.mod h1:mL1N/T3taQHkDXs73rZJwtUhF3w3ftmwwsq0BUmARs4=
 golang.org/x/net v0.0.0-20180826012351-8a410e7b638d/go.mod h1:mL1N/T3taQHkDXs73rZJwtUhF3w3ftmwwsq0BUmARs4=
 golang.org/x/net v0.0.0-20190213061140-3a22650c66bd/go.mod h1:mL1N/T3taQHkDXs73rZJwtUhF3w3ftmwwsq0BUmARs4=
 golang.org/x/net v0.0.0-20190311183353-d8887717615a h1:oWX7TPOiFAMXLq8o0ikBYfCJVlRHBcsciT5bXOrH628=
 golang.org/x/net v0.0.0-20190311183353-d8887717615a/go.mod h1:t9HGtf8HONx5eT2rtn7q6eTqICYqUVnKs3thJo3Qplg=
-golang.org/x/net v0.0.0-20190501004415-9ce7a6920f09 h1:KaQtG+aDELoNmXYas3TVkGNYRuq8JQ1aa7LJt8EXVyo=
-golang.org/x/net v0.0.0-20190501004415-9ce7a6920f09/go.mod h1:t9HGtf8HONx5eT2rtn7q6eTqICYqUVnKs3thJo3Qplg=
+golang.org/x/net v0.0.0-20190620200207-3b0461eec859 h1:R/3boaszxrf1GEUWTVDzSKVwLmSJpwZ1yqXm8j0v2QI=
+golang.org/x/net v0.0.0-20190620200207-3b0461eec859/go.mod h1:z5CRVTTTmAJ677TzLLGU+0bjPO0LkuOLi4/5GtJWs/s=
 golang.org/x/oauth2 v0.0.0-20180821212333-d2e6202438be/go.mod h1:N/0e6XlmueqKjAGxoOufVs8QHGRruUQn6yWY3a++T0U=
 golang.org/x/sync v0.0.0-20180314180146-1d60e4601c6f h1:wMNYb4v58l5UBM7MYRLPG6ZhfOqbKu7X5eyFl8ZhKvA=
 golang.org/x/sync v0.0.0-20180314180146-1d60e4601c6f/go.mod h1:RxMgew5VJxzue5/jJTE5uejpjVlOe/izrB70Jof72aM=
@@ -45,6 +46,7 @@ golang.org/x/tools v0.0.0-20190114222345-bf090417da8b/go.mod h1:n7NCudcB/nEzxVGm
 golang.org/x/tools v0.0.0-20190114222345-bf090417da8b/go.mod h1:n7NCudcB/nEzxVGmLbDWY5pfWTLqBcC2KZ6jyYvM4mQ=
 golang.org/x/tools v0.0.0-20190226205152-f727befe758c/go.mod h1:9Yl7xja0Znq3iFh3HoIrodX9oNMXvdceNzlUR8zjMvY=
 golang.org/x/tools v0.0.0-20190226205152-f727befe758c/go.mod h1:9Yl7xja0Znq3iFh3HoIrodX9oNMXvdceNzlUR8zjMvY=
+golang.org/x/tools v0.0.0-20190311212946-11955173bddd h1:/e+gpKk9r3dJobndpTytxS2gOy6m5uvpg+ISQoEcusQ=
 golang.org/x/tools v0.0.0-20190311212946-11955173bddd/go.mod h1:LCzVGOaR6xXOjkQ3onu1FJEFr0SW1gC7cKk1uF8kGRs=
 google.golang.org/appengine v1.1.0/go.mod h1:EbEs0AVv82hx2wNQdGPgUI5lhzA/G0D9YwlJXL52JkM=
 google.golang.org/appengine v1.4.0/go.mod h1:xpcJRLb0r/rnEns0DIKYYv+WjYCduHsrkT7/EB5XEv4=

trace/lrumap.go

@@ -15,23 +15,47 @@
 package trace
 
 import (
-	"github.com/hashicorp/golang-lru/simplelru"
+	"github.com/golang/groupcache/lru"
 )
 
+// A simple lru.Cache wrapper that tracks the keys of the current contents and
+// the cumulative number of evicted items.
 type lruMap struct {
-	simpleLruMap *simplelru.LRU
+	cacheKeys    map[lru.Key]bool
+	cache        *lru.Cache
 	droppedCount int
 }
 
 func newLruMap(size int) *lruMap {
-	lm := &lruMap{}
-	lm.simpleLruMap, _ = simplelru.NewLRU(size, nil)
+	lm := &lruMap{
+		cacheKeys:    make(map[lru.Key]bool),
+		cache:        lru.New(size),
+		droppedCount: 0,
+	}
+	lm.cache.OnEvicted = func(key lru.Key, value interface{}) {
+		delete(lm.cacheKeys, key)
+		lm.droppedCount++
+	}
 	return lm
 }
 
-func (lm *lruMap) add(key, value interface{}) {
-	evicted := lm.simpleLruMap.Add(key, value)
-	if evicted {
-		lm.droppedCount++
+func (lm lruMap) len() int {
+	return lm.cache.Len()
+}
+
+func (lm lruMap) keys() []interface{} {
+	keys := []interface{}{}
+	for k := range lm.cacheKeys {
+		keys = append(keys, k)
 	}
+	return keys
+}
+
+func (lm *lruMap) add(key, value interface{}) {
+	lm.cacheKeys[lru.Key(key)] = true
+	lm.cache.Add(lru.Key(key), value)
+}
+
+func (lm *lruMap) get(key interface{}) (interface{}, bool) {
+	return lm.cache.Get(key)
 }

trace/trace.go

@@ -296,7 +296,7 @@ func (s *Span) makeSpanData() *SpanData {
 	var sd SpanData
 	s.mu.Lock()
 	sd = *s.data
-	if s.lruAttributes.simpleLruMap.Len() > 0 {
+	if s.lruAttributes.len() > 0 {
 		sd.Attributes = s.lruAttributesToAttributeMap()
 		sd.DroppedAttributeCount = s.lruAttributes.droppedCount
 	}
@@ -370,8 +370,8 @@ func (s *Span) interfaceArrayToAnnotationArray() []Annotation {
 
 func (s *Span) lruAttributesToAttributeMap() map[string]interface{} {
 	attributes := make(map[string]interface{})
-	for _, key := range s.lruAttributes.simpleLruMap.Keys() {
-		value, ok := s.lruAttributes.simpleLruMap.Get(key)
+	for _, key := range s.lruAttributes.keys() {
+		value, ok := s.lruAttributes.get(key)
 		if ok {
 			keyStr := key.(string)
 			attributes[keyStr] = value