go-delve/delve · error

you must specify a thread

Error message

you must specify a thread

What it means

The 'thread' command requires a numeric thread ID argument; this error is returned when it is invoked with no argument. Delve cannot switch threads without knowing which one to target.

Source

Thrown at pkg/terminal/command.go:849

		}
		prefix := "  "
		if state.CurrentThread != nil && state.CurrentThread.ID == th.ID {
			prefix = "* "
		}
		if th.Function != nil {
			fmt.Fprintf(t.stdout, "%sThread %d at %#v %s:%d %s\n",
				prefix, th.ID, th.PC, t.formatPath(th.File),
				th.Line, th.Function.Name())
		} else {
			fmt.Fprintf(t.stdout, "%sThread %s\n", prefix, t.formatThread(th))
		}
	}
	return nil
}

func thread(t *Term, ctx callContext, args string) error {
	if len(args) == 0 {
		return errors.New("you must specify a thread")
	}
	tid, err := strconv.Atoi(args)
	if err != nil {
		return err
	}
	oldState, err := t.client.GetState()
	if err != nil {
		return err
	}
	newState, err := t.client.SwitchThread(tid)
	if err != nil {
		return err
	}

	oldThread := "<none>"
	newThread := "<none>"
	if oldState.CurrentThread != nil {
		oldThread = strconv.Itoa(oldState.CurrentThread.ID)

View on GitHub (pinned to a23773e6c3)

Solutions

1. Run 'threads' first to list available thread IDs
2. Use 'thread <id>' with a numeric ID, e.g. 'thread 3'
3. Use 'goroutine <n>' if you actually meant to switch goroutines

Example fix

// before
(dlv) thread
// after
(dlv) threads
(dlv) thread 5

// Ensure a numeric thread id is provided
parts := strings.Fields(args)
if len(parts) != 1 {
    return errors.New("usage: thread <tid>")
}
if _, err := strconv.Atoi(parts[0]); err != nil {
    return fmt.Errorf("thread id must be an integer: %v", err)
}

err := term.ExecuteCommand("thread " + args)
if err != nil && strings.Contains(err.Error(), "you must specify a thread") {
    // list threads and prompt for an id
st, _ := client.ListThreads()
    printThreadChoices(st)
}

When it happens

Trigger: Typing 'thread' alone at the (dlv) prompt instead of 'thread <tid>'.

Common situations: Habit from other debuggers where 'thread' lists or selects interactively; forgetting the ID after checking 'threads'.

Understand the failure class

Background: "missing required argument" and "the following required arguments were not provided": what required-argument errors mean and how to fix them — this error's family across 20 libraries.

Related errors

• command not available
• too many arguments to goroutine
• not enough arguments
• Invalid frame %d
• Backtick not supported in '%s'

AI-assisted analysis of go-delve/delve@a23773e6c3 (2026-08-31). Data as JSON: /api/errors/eee83789825be92b. Report an issue: GitHub.