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diff --git a/README.md b/README.md
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+# gjl
+Goの並列処理をテストのために  
+[Go is not an easy language](https://www.arp242.net/go-easy.html)  
+
+## Dev
+```bash
+go run main.go
+```
+or
+```bash
+go build -o gjl main.go
+./main.go
+```
+
diff --git a/gjl b/gjl
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--- /dev/null
+++ b/gjl
diff --git a/go.mod b/go.mod
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+module gjl
+
+go 1.23.4
diff --git a/main.go b/main.go
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+package main
+
+import (
+	"fmt"
+	"sync"
+	"time"
+)
+
+func main() {
+	var (
+		jobs    = 20                 // Run 20 jobs in total.
+		running = make(chan bool, 3) // Limit concurrent jobs to 3.
+		wg      sync.WaitGroup       // Keep track of which jobs are finished.
+	)
+
+	wg.Add(jobs)
+	for i := 1; i <= jobs; i++ {
+		running <- true // Fill running; this will block and wait if it's already full.
+
+		// Start a job.
+		go func(i int) {
+			defer func() {
+				<-running // Drain running so new jobs can be added.
+				wg.Done() // Signal that this job is done.
+			}()
+
+			// "do work"
+			time.Sleep(1 * time.Second)
+			fmt.Println(i)
+		}(i)
+	}
+
+	wg.Wait() // Wait until all jobs are done.
+	fmt.Println("done")
+}