Plugin custom Action Hook not working

I am trying to create one basic plugin where I want to create my own action hook. Here is the code for the same.

<?php
/*
Plugin Name: Demo Plugin
Version: 1.0
*/

do_action('basic_action_demo');
?>

Now after activating this plugin I want to use this action hook in my current theme’s function.php file, code for the same is as below:

add_action('basic_action_demo','action_demo');

function action_demo()
{
    echo "I am inside";
}

Now the problem is my hooked action never gets called, we can see that do_action is called unconditionally so it will be called on each page load but it never gets into “action_demo” method.

What I have figured out far is plugin is loaded before my theme’e function.php file is executed. So here do_action is called first and then add_action.

A hint would be really appreciated.

Update:

Below plugin action works.

<?php
/*
Plugin Name: Demo Plugin
Version: 1.0
*/

add_action('basic_action_demo','action_demo');
do_action('basic_action_demo');

function action_demo()
{
    echo "I am Inside";
    die;
}
?>

Your plugin needs to wait for the themes functions.php file to be loaded. Try this:

<?php
/*
Plugin Name: Demo Plugin
Version: 1.0
*/

add_action( 'after_setup_theme', function() {
    do_action( 'basic_action_demo' );
} );
?>

The after_setup_theme hook is run immediately after functions.php is loaded.

Update for your comment below.
In your plugin create a function for your form:

<?php
/*
Plugin Name: Demo Plugin
Version: 1.0
*/

function output_my_form () {
    echo "I'm a form";
    // do your action here
    do_action( 'basic_action_demo' );
}
?>

Then in your theme’s functions.php:

if ( function_exists( 'output_my_form' ) ) {
    output_my_form();
}

This is a simple example. In reality you would want to call that function from a form.php in your theme.