Why does it not create many threads when many goroutines are blocked in writing file in golang?

Question

As we know in go, a thread may be created when the goroutine has to perform a blocking call, such as a system call, or a call to a C library via cgo. Some test code:

Answer 1

I altered your program slightly to output a much bigger block

package main

import (
    "io/ioutil"
    "os"
    "runtime"
    "strconv"
)

func main() {
    runtime.GOMAXPROCS(2)
    data := make([]byte, 128*1024*1024)
    for i := 0; i < 200; i++ {
        go func(n int) {
            for {
                err := ioutil.WriteFile("testxxx"+strconv.Itoa(n), []byte(data), os.ModePerm)
                if err != nil {
                    println(err)
                    break
                }
            }
        }(i)
    }
    select {}
}

This then shows >200 threads as you expected

$ cat /proc/17033/status | grep -i thread
Threads:    203

So I think the syscalls were exiting too quickly in your original test to show the effect you were expecting.