From 11218a95d08f5f508bc27aba23278af93a56480d Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Jan-Otto=20Kr=C3=B6pke?= <joe@cloudeteer.de>
Date: Mon, 10 Jul 2023 13:59:57 +0200
Subject: [PATCH] Implement Lazy Loading of NameTable
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Content-Transfer-Encoding: 8bit

Signed-off-by: Jan-Otto Kröpke <mail@jkroepke.de>
---
 collector/perflib.go |  4 +--
 perflib/nametable.go | 86 ++++++++++++++++++++++++--------------------
 perflib/perflib.go   |  5 +--
 3 files changed, 50 insertions(+), 45 deletions(-)

diff --git a/collector/perflib.go b/collector/perflib.go
index ab646480..743c797d 100644
--- a/collector/perflib.go
+++ b/collector/perflib.go
@@ -12,10 +12,8 @@ import (
 	"github.com/go-kit/log/level"
 )
 
-var nametable = perflib.CounterNameTable
-
 func MapCounterToIndex(name string) string {
-	return strconv.Itoa(int(nametable.LookupIndex(name)))
+	return strconv.Itoa(int(perflib.CounterNameTable.LookupIndex(name)))
 }
 
 func getPerflibSnapshot(objNames string) (map[string]*perflib.PerfObject, error) {
diff --git a/perflib/nametable.go b/perflib/nametable.go
index cd717e4f..b10a7610 100644
--- a/perflib/nametable.go
+++ b/perflib/nametable.go
@@ -4,6 +4,7 @@ import (
 	"bytes"
 	"fmt"
 	"strconv"
+	"sync"
 )
 
 // Initialize global name tables
@@ -18,54 +19,63 @@ func (p *perfObjectType) LookupName() string {
 }
 
 type NameTable struct {
-	byIndex  map[uint32]string
-	byString map[string]uint32
+	once sync.Once
+
+	name string
+
+	table struct {
+		index  map[uint32]string
+		string map[string]uint32
+	}
 }
 
 func (t *NameTable) LookupString(index uint32) string {
-	return t.byIndex[index]
+	t.initialize()
+	return t.table.index[index]
 }
 
 func (t *NameTable) LookupIndex(str string) uint32 {
-	return t.byString[str]
+	t.initialize()
+	return t.table.string[str]
 }
 
 // QueryNameTable Query a perflib name table from the registry. Specify the type and the language
 // code (i.e. "Counter 009" or "Help 009") for English language.
 func QueryNameTable(tableName string) *NameTable {
-	nameTable := new(NameTable)
-	nameTable.byIndex = make(map[uint32]string)
-
-	buffer, err := queryRawData(tableName)
-	if err != nil {
-		panic(err)
+	return &NameTable{
+		name: tableName,
 	}
-	r := bytes.NewReader(buffer)
-	for {
-		index, err := readUTF16String(r)
-		if err != nil {
-			break
-		}
-
-		desc, err := readUTF16String(r)
-		if err != nil {
-			break
-		}
-
-		indexInt, _ := strconv.Atoi(index)
-
-		if err != nil {
-			panic(fmt.Sprint("Invalid index ", index))
-		}
-
-		nameTable.byIndex[uint32(indexInt)] = desc
-	}
-
-	nameTable.byString = make(map[string]uint32)
-
-	for k, v := range nameTable.byIndex {
-		nameTable.byString[v] = k
-	}
-
-	return nameTable
+}
+
+func (t *NameTable) initialize() {
+	t.once.Do(func() {
+		t.table.index = make(map[uint32]string)
+		t.table.string = make(map[string]uint32)
+
+		buffer, err := queryRawData(t.name)
+		if err != nil {
+			panic(err)
+		}
+		r := bytes.NewReader(buffer)
+		for {
+			index, err := readUTF16String(r)
+			if err != nil {
+				break
+			}
+
+			desc, err := readUTF16String(r)
+			if err != nil {
+				break
+			}
+
+			if err != nil {
+				panic(fmt.Sprint("Invalid index ", index))
+			}
+
+			indexInt, _ := strconv.Atoi(index)
+
+			t.table.index[uint32(indexInt)] = desc
+			t.table.string[desc] = uint32(indexInt)
+		}
+	})
 }
diff --git a/perflib/perflib.go b/perflib/perflib.go
index b4366aba..e6e1d78c 100644
--- a/perflib/perflib.go
+++ b/perflib/perflib.go
@@ -175,9 +175,6 @@ type PerfCounter struct {
 	SecondValue int64
 }
 
-// Error value returned by RegQueryValueEx if the buffer isn't sufficiently large
-const errorMoreData = syscall.Errno(syscall.ERROR_MORE_DATA)
-
 var (
 	bufLenGlobal = uint32(400000)
 	bufLenCostly = uint32(2000000)
@@ -223,7 +220,7 @@ func queryRawData(query string) ([]byte, error) {
 			(*byte)(unsafe.Pointer(&buffer[0])),
 			&bufLen)
 
-		if err == errorMoreData {
+		if err == error(syscall.ERROR_MORE_DATA) {
 			newBuffer := make([]byte, len(buffer)+16384)
 			copy(newBuffer, buffer)
 			buffer = newBuffer