Merge pull request #710 from devlights:add-heapalloc-with-clone-method

Add using strings.Clone() example

examples/singleapp/using_clone_method/.gitignore

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+app

examples/singleapp/using_clone_method/README.md

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+# これは何？
+
+Go 1.18 で追加された ```strings.Clone()``` を利用したサンプルです。
+
+内部で大きな文字列を確保している状態で、それらの部分文字列を別の場所に確保する処理を実施しています。
+
+現状（2023-12-05 現在）のGoの標準コンパイラでは、元の文字列と部分文字列は同じメモリデータを共有するので
+
+部分文字列をシャローコピーして別のストアに保持したままだと、メモリが開放されません。
+
+```strings.Clone()``` を利用することにより、ディープコピーが行われるので、メモリが開放されるようになります。
+
+## 実行例
+
+```sh
+$ task
+task: [build] go build -o app main.go
+task: [run-not-use-clone] ./app
+Title           HeapAlloc       HeapObjects
+[start     ]      192792             144
+[gen       ]    11482528            4576
+[store     ]    11487008            4588
+[checkpoint]     8471296            1363
+[checkpoint]     8475728            1372
+[checkpoint]     8475728            1372
+[checkpoint]     8475728            1372
+[checkpoint]     8475736            1373
+task: [run-use-clone] ./app -use
+Title           HeapAlloc       HeapObjects
+[start     ]      192824             144
+[gen       ]    11497632            4607
+[store     ]    11507440            4952
+[checkpoint]      296112             724
+[checkpoint]      300536             732
+[checkpoint]      300536             732
+[checkpoint]      300544             733
+[checkpoint]      300544             733
+```

examples/singleapp/using_clone_method/Taskfile.yml

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+# https://taskfile.dev
+
+version: '3'
+
+tasks:
+  default:
+    deps: [ build ]
+    cmds:
+      - task: run-not-use-clone
+      - task: run-use-clone
+  build:
+    cmds:
+      - go build -o app main.go
+  run-not-use-clone:
+    cmds:
+      - ./app
+  run-use-clone:
+    cmds:
+      - ./app -use

examples/singleapp/using_clone_method/main.go

@@ -0,0 +1,108 @@
+package main
+
+import (
+	"flag"
+	"io"
+	"log"
+	"os/exec"
+	"runtime"
+	"strings"
+	"unsafe"
+)
+
+const (
+	NUM_ITEMS = 1000
+	SHELL     = "/bin/bash"
+)
+
+var (
+	store = make([]string, NUM_ITEMS)
+)
+
+func init() {
+	log.SetFlags(0)
+}
+
+func mem(prefix string) {
+	var (
+		m = runtime.MemStats{}
+	)
+
+	runtime.ReadMemStats(&m)
+	log.Printf("[%s]\t%8d\t%8d\n", prefix, m.HeapAlloc, m.HeapObjects)
+}
+
+func gen() []string {
+	var (
+		l = make([]string, NUM_ITEMS)
+	)
+
+	for i := 0; i < NUM_ITEMS; i++ {
+		output, _ := exec.Command(SHELL, "-c", "openssl rand -base64 4096 | tr -d '\n'").Output()
+		l[i] = unsafe.String(&output[0], len(output))
+	}
+
+	return l
+}
+
+func main() {
+	log.Println("Title       \tHeapAlloc\tHeapObjects")
+	mem("start     ")
+
+	var (
+		use = flag.Bool("use", false, "Use strings.Clone()")
+	)
+	flag.Parse()
+
+	var (
+		l = gen()
+	)
+	mem("gen       ")
+
+	for i := 0; i < NUM_ITEMS; i++ {
+		storeValue := l[i][:5]
+
+		if *use {
+			store[i] = strings.Clone(storeValue)
+		} else {
+			store[i] = storeValue
+		}
+	}
+	mem("store     ")
+
+	runtime.GC()
+
+	for i, v := range store {
+		if i%200 == 0 {
+			runtime.GC()
+			mem("checkpoint")
+		}
+
+		io.Discard.Write(unsafe.Slice(unsafe.StringData(v), len(v)))
+	}
+
+	/*
+		$ task
+		task: [build] go build -o app main.go
+		task: [run-not-use-clone] ./app
+		Title           HeapAlloc       HeapObjects
+		[start     ]      192792             144
+		[gen       ]    11482528            4576
+		[store     ]    11487008            4588
+		[checkpoint]     8471296            1363
+		[checkpoint]     8475728            1372
+		[checkpoint]     8475728            1372
+		[checkpoint]     8475728            1372
+		[checkpoint]     8475736            1373
+		task: [run-use-clone] ./app -use
+		Title           HeapAlloc       HeapObjects
+		[start     ]      192824             144
+		[gen       ]    11497632            4607
+		[store     ]    11507440            4952
+		[checkpoint]      296112             724
+		[checkpoint]      300536             732
+		[checkpoint]      300536             732
+		[checkpoint]      300544             733
+		[checkpoint]      300544             733
+	*/
+}