golang/go #52086 reproduction

main.go

package main

import (
	"bytes"
	"context"
	"fmt"
	"net"
	"os"
	"os/exec"
	"time"
)


// This reproduces the process hang described in https://github.com/golang/go/issues/52086 around once every 1200 executions
// I was seemingly able to reproduce the issue more frequently before removing several channels and time based selects, but 
// this code is simpler and still triggers the issue fast enough when compiled and then executed inside a for loop on a shell
// using something like the following fish shell snippet:
// go build .; for i in (seq 1 100000); echo "Iteration $i"; ./repro-52086; end;
// 
// Note: __CF_USER_TEXT_ENCODING must be set in the environment for this to reproduce ths issue
// ex. `set -x __CF_USER_TEXT_ENCODING "$uidInHex:0x0:0x0"` where uid in hex is your OS X user id encoded as a `0x000` format hex value
// If you are using iTerm 2 or Alacritty as your terminal this is likely already set, 
// if you are using Apple Terminal, it likely is not set by default and 
// you will need to set it yourself in order to reproduce the process hang
func main() {
	// removing the tcp dial altogether or taking it out of the goroutine causes the issue not to reproduce
	go func() {
		var d net.Dialer
		conn, err := d.DialContext(context.Background(), "tcp", "google.com:443")
		if err == nil {
			defer conn.Close()
		} else {
			fmt.Printf("error dial: %v", err)
		}
	}()

	result, err := execCmd()
	if err != nil {
		fmt.Printf("error exec: %v", err)
		os.Exit(1)
	}
	fmt.Printf("exec returned: %v", result)
}

func execCmd() (string, error) {
	cmd := exec.Command("echo", time.Now().String())
	cmd.Env = []string{}

	var stdout, stderr bytes.Buffer
	cmd.Stdout = &stdout
	cmd.Stderr = &stderr
	if err := cmd.Run(); err != nil {
		return "", fmt.Errorf("%q: %w", stderr.String(), err)
	}

	return stdout.String(), nil
}