From f9e2fb6b87e207c586332667d6f5ab5bdb51becc Mon Sep 17 00:00:00 2001
From: Brad Moylan <bmoylan@palantir.com>
Date: Thu, 7 Sep 2023 19:29:10 -0700
Subject: [PATCH] improvement: Use go1.21's slices package to avoid allocation
 in sorting (#323)

---
 metrics/registry.go   |  5 ++---
 metrics/sort.go       | 23 +++++++++++++++++++++++
 metrics/sort_go121.go | 30 ++++++++++++++++++++++++++++++
 3 files changed, 55 insertions(+), 3 deletions(-)
 create mode 100644 metrics/sort.go
 create mode 100644 metrics/sort_go121.go

diff --git a/metrics/registry.go b/metrics/registry.go
index 8848bcd8..24638e4c 100644
--- a/metrics/registry.go
+++ b/metrics/registry.go
@@ -6,7 +6,6 @@ package metrics
 
 import (
 	"context"
-	"sort"
 	"strings"
 	"sync"
 	"time"
@@ -269,7 +268,7 @@ func (r *rootRegistry) Each(f MetricVisitor) {
 		sortedMetricIDs = append(sortedMetricIDs, name)
 		allMetrics[name] = metric
 	})
-	sort.Strings(sortedMetricIDs)
+	sortStrings(sortedMetricIDs)
 
 	for _, id := range sortedMetricIDs {
 		r.idToMetricMutex.RLock()
@@ -401,6 +400,6 @@ func toMetricTagsID(name string, tags Tags) metricTagsID {
 // newSortedTags copies the tag slice before sorting so that in-place mutation does not affect the input slice.
 func newSortedTags(tags Tags) Tags {
 	tagsCopy := append(tags[:0:0], tags...)
-	sort.Sort(tagsCopy)
+	sortTags(tagsCopy)
 	return tagsCopy
 }
diff --git a/metrics/sort.go b/metrics/sort.go
new file mode 100644
index 00000000..54104372
--- /dev/null
+++ b/metrics/sort.go
@@ -0,0 +1,23 @@
+// Copyright (c) 2023 Palantir Technologies. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+//go:build !go1.21
+
+package metrics
+
+import (
+	"sort"
+)
+
+// sortStrings is the default sort.Strings function.
+// Unfortunately this forces the slice to escape to the heap.
+// See https://github.com/golang/go/issues/17332
+// Go 1.21's slices package does not have this issue.
+var sortStrings = sort.Strings
+
+// sortTags is the default sort.Sort function.
+// Unfortunately this forces the slice to escape to the heap.
+// See https://github.com/golang/go/issues/17332
+// Go 1.21's slices package does not have this issue.
+var sortTags = sort.Sort
diff --git a/metrics/sort_go121.go b/metrics/sort_go121.go
new file mode 100644
index 00000000..d5abb8e6
--- /dev/null
+++ b/metrics/sort_go121.go
@@ -0,0 +1,30 @@
+// Copyright (c) 2023 Palantir Technologies. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+//go:build go1.21
+
+package metrics
+
+import (
+	"slices"
+)
+
+// sortStrings is the default slices.Sort function which does not force allocation like sort.Strings.
+var sortStrings = slices.Sort[[]string]
+
+// sortTags uses slices.SortFunc which does not force allocation like sort.Sort.
+func sortTags(tags Tags) {
+	slices.SortFunc(tags, compareTags)
+}
+
+func compareTags(a, b Tag) int {
+	switch {
+	case a.keyValue > b.keyValue:
+		return 1
+	case a.keyValue == b.keyValue:
+		return 0
+	default:
+		return -1
+	}
+}