For the below code:

package main

import (
    "fmt"
    "syscall"
)

func block(c chan bool) {
    fmt.Println("block() enter")
    buf := make([]byte, 1024)
    _, _ = syscall.Read(0, buf) // block on doing an unbuffered read on STDIN
    fmt.Println("block() exit")
    c <- true // main() we're done
}

func main() {
    c := make(chan bool)
    for i := 0; i < 1000; i++ {
        go block(c)
    }
    for i := 0; i < 1000; i++ {
        <-c
    }
}

Ubuntu 12.04 reported 1004 OS threads for that process.

If Goroutine(G1) blocks(for syscall.Read()) on OS thread(M1), as shown below:

$ go version
go version go1.20.2 linux/amd64

How does Goroutine(G1) complete the blocking system call(syscall.Read()) on OS thread(M1), before moving back to LRQ? Doesn’t OS thread(M1) need CPU core to complete blocking system call?