Merge pull request #561 from devlights/add-map-race-example

Author: devlights

examples/singleapp/map_is_not_threadsafe/Taskfile.yml

@@ -0,0 +1,21 @@
+version: '3'
+
+tasks:
+  fmt:
+    cmds:
+      - go fmt ./...
+  vet:
+    cmds:
+      - go vet ./...
+  run:
+    cmds:
+      - cmd: for i in {1..10} ; do go run race/main.go; done
+        silent: true
+  run-notrace:
+    cmds:
+      - cmd: for i in {1..10} ; do go run -race notrace/main.go; done
+        silent: true
+  run-with-raceoption:
+    cmds:
+      - cmd: go run -race race/main.go
+        ignore_error: true

examples/singleapp/map_is_not_threadsafe/notrace/main.go

@@ -0,0 +1,58 @@
+// マップ操作 はスレッドセーフでは無いというのを示すサンプルです。
+// 本サンプルはデータ競合が発生しません。
+//
+// REFERENCES:
+//   - https://stackoverflow.com/questions/44152988/append-not-thread-safe
+//   - https://stackoverflow.com/questions/49879322/can-i-concurrently-write-different-slice-elements
+package main
+
+import (
+	"flag"
+	"fmt"
+	"strconv"
+	"sync"
+)
+
+func main() {
+	var (
+		verbose = flag.Bool("verbose", false, "verbose output")
+	)
+	flag.Parse()
+
+	var (
+		mu sync.Mutex
+		src = make(map[string]bool)
+		dst = make(map[string]bool)
+	)
+
+	for i := 0; i < 5; i++ {
+		src[strconv.Itoa(i)] = true
+	}
+
+	wg := sync.WaitGroup{}
+	for k, v := range src {
+		wg.Add(1)
+		go func(k string, v bool) {
+			defer wg.Done()
+
+			mu.Lock()
+			dst[k] = v
+			mu.Unlock()
+		}(k, v)
+	}
+
+	wg.Wait()
+
+	fmt.Printf("src-len=%d\tdst-len=%d\n", len(src), len(dst))
+
+	if *verbose {
+		fmt.Println("=========== SRC ===========")
+		for _, v := range src {
+			fmt.Println(v)
+		}
+		fmt.Println("=========== DST ===========")
+		for _, v := range dst {
+			fmt.Println(v)
+		}
+	}
+}

examples/singleapp/map_is_not_threadsafe/race/main.go

@@ -0,0 +1,55 @@
+// マップ操作 はスレッドセーフでは無いというのを示すサンプルです。
+// 本サンプルはデータ競合が発生しています。
+//
+// REFERENCES:
+//   - https://stackoverflow.com/questions/44152988/append-not-thread-safe
+//   - https://stackoverflow.com/questions/49879322/can-i-concurrently-write-different-slice-elements
+package main
+
+import (
+	"flag"
+	"fmt"
+	"strconv"
+	"sync"
+)
+
+func main() {
+	var (
+		verbose = flag.Bool("verbose", false, "verbose output")
+	)
+	flag.Parse()
+
+	var (
+		src = make(map[string]bool)
+		dst = make(map[string]bool)
+	)
+
+	for i := 0; i < 5; i++ {
+		src[strconv.Itoa(i)] = true
+	}
+
+	wg := sync.WaitGroup{}
+	for k, v := range src {
+		wg.Add(1)
+		go func(k string, v bool) {
+			defer wg.Done()
+
+			dst[k] = v
+		}(k, v)
+	}
+
+	wg.Wait()
+
+	fmt.Printf("src-len=%d\tdst-len=%d\n", len(src), len(dst))
+
+	if *verbose {
+		fmt.Println("=========== SRC ===========")
+		for _, v := range src {
+			fmt.Println(v)
+		}
+		fmt.Println("=========== DST ===========")
+		for _, v := range dst {
+			fmt.Println(v)
+		}
+	}
+}