PHP中的单例引用和递归

Question

I have a main bootstrap class (singleton1 in the example bellow) that instantiates some singleton classes. In those singleton classes, I need to keep a reference to the app main class for easy and quick reference to it, but doing so gives me a:

Fatal error: Maximum function nesting level of '100' reached, aborting

Here is the exmaple code:

<?php

class Singleton1 {

    private static $instance;


    private function __construct() {

        Singleton2::instance();

    }

    public static function instance () {

        if( !self::$instance ) {
            $class = __CLASS__;
            self::$instance = new $class;
        }

        return self::$instance;
    }

    public function test () {
        echo 'Good.';
    }

    private function __clone() { }

    private function __wakeup() { }

}

class Singleton2 {

    private static $instance;

    private $singleton1;

    private function __construct() {
        $this->singleton1 = Singleton1::instance();
    }

    public static function instance () {

        if( !self::$instance ) {
            $class = __CLASS__;
            self::$instance = new $class;
        }

        return self::$instance;
    }

    public function test () {
        $this->singleton1->test();
    }

    private function __clone() { }

    private function __wakeup() { }

}

Singleton1::instance();

Singleton2::instance()->test();

I can't find any logical explanation to the issue ...

Thanks.

Answer 1

Your code has the following loop:

Singleton2::__construct()
Singleton1::instance()
Singleton1::__construct()
Singleton2::instance()
Singleton2::__construct()