go - Will time.Sleep block goroutine?

Question

I have next code:

par.go

package main

import (
    "runtime";
    "time"
)

func main() {
    runtime.GOMAXPROCS(4)
    ch := make(chan int)
    n := 1
    for i := 0; i < n; i++ {
        go func() {
            time.Sleep(60 * time.Second)
            ch <- 1
        }();
    }
    for i := 0; i < n; i++ {
        <-ch
    }
}

I use next to run it:

$ go build par.go
$ time ./par

Then, confirm how many threads in this process:

$ ps -ef | grep par
shubunt+  3670 32131  0 12:35 pts/0    00:00:00 ./par
$ cat /proc/3670/status | grep -i threads
Threads:        5

You can see there are 5 threads.

If I change the value of n in code, then situations are next:

n := 100, Threads is 8
n := 10000, Threads is 9
n := 100000, Threads is 9
n := 1000000, Threads is 9
n := 2000000, Threads is 10

I know, go scheduler follow MPG model, here P = 4, so M = 4, M is 1:1 with KSE(Kernel threads). If any goroutine in any blocking status, the P will detached from current M, and find a idle M or new a M if can't find.

So, my question is: is time.Sleep really blocking goroutine? If not, why new threads there when I increase value of n from 1 to 2000000? If yes, there is 60 seconds there, why just scheduler new a little new M, I expect a lots of new threads there?

UPDATE:

Add another example from this.

test.go:

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 {}
}

If not use Sleep, use real IO, the threads number will be 202 on my machine.

So, my question also related to the difference of above 2 examples, when I should worry about scheduler generate too many kernel threads for me?

Answer 1

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