A look at modern PHP(lwn.net)

  I once asked Rasmus about this face-to-face, during one of his presentations, specifically his thoughts about the pThread extension (https://www.php.net/manual/en/intro.pthreads.php), and he responded that it was not required in a web context, as web servers already have threads per request so its a mute point.

  pretty hard to proceed with some code that works with a DB when the connection can't be established, so proceed with what exactly other than error handling? 

  is a synchronous thread, as described above above. By design.

    /**
     * Method for converting Foos into Bars
     *
     * @param Foo[] $foos
     * @return Bar[]
     */
    function convertFoosToBars(array $foos): array
    {
        // ...
    }