pushing a class instance to the queue from outside of the plugin init

[gkv-ckultzow]

Solving this took a good twenty hours of my life away, and maybe it's "common sense" but I thought it might be good to keep here as a note for some future troubleshooting reference.

The example plugin works on page load by checking GET for process and nonce, then pushing strings to the queue.

For my logic, I needed two changes: a class instance be pushed to the queue instead of a string, and the trigger to be a php function called by AJAX, which I declared in functions.php like this:

$instance = new Example_Background_Processing()
$instance->handle_all();

after adjusting handle_all to public, and having handle_all instantiate instances of a class to push_to_queue, instead of the names.

When WP_Background_Process->task($item) is called this way, rather than from the plugin declaration, PHP often - but importantly, not always! - does not recognize the class of the instantiated class object being pushed to the queue as having been declared, and re-casts that object as __PHP_Incomplete_Class containing the instantiated object.

This adds an extra layer, breaking references to variables in functions. But if you're testing this several times in a row, sometimes the background process DOES recognize the class, and lets it go through as intended. Which is awesome for troubleshooting.

So, in order to call this handle_all function via AJAX in functions.php, I needed to include/define the class that I was creating and passing to task($item) at the top of functions.php, even though it wasn't being used until handle_all(), which allowed PHP to always see the class as correctly defined during task($item), and not recast it.