internal: cache build info to reduce lock contention

internal/gitmetadata.go

@@ -43,6 +43,7 @@ var (
 	lock = sync.Mutex{}
 
 	gitMetadataTags map[string]string
+	buildInfo       *debug.BuildInfo
 )
 
 func updateTags(tags map[string]string, key string, value string) {
@@ -76,13 +77,25 @@ func getTagsFromDDTags() map[string]string {
 	}
 }
 
-// getTagsFromBinary extracts git metadata from binary metadata
-func getTagsFromBinary() map[string]string {
-	res := make(map[string]string)
-	info, ok := debug.ReadBuildInfo()
-	if !ok {
-		log.Debug("ReadBuildInfo failed, skip source code metadata extracting")
-		return res
+// getTagsFromBinary extracts git metadata from binary metadata.
+// It assumes it's running under a locked mutex.
+func getTagsFromBinary(readBuildInfo func() (*debug.BuildInfo, bool)) map[string]string {
+	var (
+		info *debug.BuildInfo
+		res  = make(map[string]string)
+	)
+	if buildInfo == nil {
+		var ok bool
+		info, ok = readBuildInfo()
+		if !ok {
+			// Initialize buildInfo to avoid multiple calls to debug.ReadBuildInfo.
+			buildInfo = &debug.BuildInfo{}
+			log.Debug("ReadBuildInfo failed, skip source code metadata extracting")
+			return res
+		}
+		buildInfo = info
+	} else {
+		info = buildInfo
 	}
 	goPath := info.Path
 	var vcs, commitSha string
@@ -116,7 +129,7 @@ func GetGitMetadataTags() map[string]string {
 	if BoolEnv(EnvGitMetadataEnabledFlag, true) {
 		updateAllTags(gitMetadataTags, getTagsFromEnv())
 		updateAllTags(gitMetadataTags, getTagsFromDDTags())
-		updateAllTags(gitMetadataTags, getTagsFromBinary())
+		updateAllTags(gitMetadataTags, getTagsFromBinary(debug.ReadBuildInfo))
 	}
 
 	return gitMetadataTags

internal/gitmetadata_test.go

@@ -6,6 +6,7 @@
 package internal
 
 import (
+	"runtime/debug"
 	"testing"
 
 	"github.com/stretchr/testify/assert"
@@ -54,3 +55,83 @@ func TestRemoveCredentials(t *testing.T) {
 		})
 	}
 }
+
+func TestGetTagsFromBinary(t *testing.T) {
+	testCases := []struct {
+		name     string
+		in       string
+		expected map[string]string
+	}{
+		{
+			name:     "empty build info",
+			expected: map[string]string{},
+		},
+		{
+			name: "build info with module path",
+			expected: map[string]string{
+				TagGoPath: "github.com/DataDog/dd-trace-go",
+			},
+		},
+		{
+			name: "build info with module path and git repository",
+			expected: map[string]string{
+				TagGoPath:    "github.com/DataDog/dd-trace-go",
+				TagCommitSha: "123456",
+			},
+		},
+	}
+	for _, tc := range testCases {
+		t.Run(tc.name, func(t *testing.T) {
+			readBuildInfo := func() (*debug.BuildInfo, bool) {
+				info := &debug.BuildInfo{
+					Settings: []debug.BuildSetting{
+						{
+							Key:   "vcs",
+							Value: "git",
+						},
+					},
+				}
+				if tc.expected[TagGoPath] != "" {
+					info.Path = tc.expected[TagGoPath]
+				}
+				if tc.expected[TagCommitSha] != "" {
+					info.Settings = append(info.Settings, debug.BuildSetting{
+						Key:   "vcs.revision",
+						Value: tc.expected[TagCommitSha],
+					})
+				}
+				return info, true
+			}
+			tags := getTagsFromBinary(readBuildInfo)
+			assert.Subset(t, tags, tc.expected)
+			buildInfo = nil
+		})
+	}
+}
+
+func TestGetTagsFromBinaryCache(t *testing.T) {
+	var called int
+	readBuildInfo := func() (*debug.BuildInfo, bool) {
+		called++
+		info := &debug.BuildInfo{
+			Settings: []debug.BuildSetting{
+				{
+					Key:   "vcs",
+					Value: "git",
+				},
+				{
+					Key:   "vcs.revision",
+					Value: "123456",
+				},
+			},
+		}
+		return info, true
+	}
+	tags := getTagsFromBinary(readBuildInfo)
+	assert.NotEmpty(t, tags)
+	for i := 0; i < 10; i++ {
+		res := getTagsFromBinary(readBuildInfo)
+		assert.Equal(t, tags, res)
+	}
+	assert.Equal(t, 1, called)
+}