trap is ignored when dialog is running with custom BASH_XTRACEFD

Question

I have following script

#!/bin/bash

exec 5> >(logger -t $0)
BASH_XTRACEFD="5"
set -x

trap _reboot INT

DIALOG_TITLE="This is fancy dialog title"

_reboot() {
        echo Exiting
        exit
}

dialog --title "${DIALOG_TITLE}" --yesno "Welcome to Dialog" 0 0

However when i do CTRL+C, script is exited without printing anything. If i remove either set -x or BASH_XTRACEFD="5" it will work fine and trap is caught and _reboot function is executed. But if i leave both in (which i need for debugging purposes) - then trap looses all meaning.

Exit code is 141 which is interesting when i exit with CTRL+C. If i let the script run it's natural course it will exit with 0 However if i remove either of set -x or BASH_XTRACEFD="5" and then CTRL+C i will exit with 55 then.

This for some reason happens only while dialog is on screen. For example if i do

while true; do
  sleep 5
done

And then exit with CTRL+C trap will be executed.

I need help figuring this thing out.

EDIT: Might be worth mentioning that bash version is 5.1.16, running on Alpine 3.16

Answer 1

dialog uses ncurses, which captures SIGINT, as documented in the initscr manpage section on Signal Handlers:

SIGINT
The handler attempts to cleanup the screen on exit. Although it usually works as expected, there are limitations:

• Walking the SCREEN list is unsafe, since all list management is done without any signal blocking.
• On systems which have REENTRANT turned on, set_term uses functions which could deadlock or misbehave in other ways.
• endwin calls other functions, many of which use stdio or other library functions which are clearly unsafe.

bash would only "see" the signal when the child process does not catch it first.