sales_quote_save_before observer executing twice

I have an observer that observes the sales_quote_save_before event and it executes twice when items are added to the cart, removed from the cart, or updated in the cart.

I assume that the save_befo开发者_如何转开发re (and, for that matter, the save_after event) are somewhere being triggered more than once.

I would like to know why / where this happens, and how to limit the observer to only executing once.

I have tried the solution offered here: Magento - customer_save_after always fired twice, but my observer still executes twice (when I log execution with Mage::log(), the timestamp is 1 second different).

Any help is much appreciated.

What I ended up doing to solve the issue was comparing the updated_at value of the $observer object to the current time. If the last update was more than 3 seconds ago (completely arbitrary value), I let the observer execute, otherwise I return. This worked for me because the two instances of my observer always fired within 1-2 seconds.

I recognize this is not the best solution, since it does not account for server load or other latency issues, so if somebody can think of a better solution, I would appreciate the feedback.

    $updatedAt = date('U', strtotime($observer->getQuote()->getUpdatedAt()));
    $now = time();
    if(($updatedAt + 3) > $now){
        return $this; //the observer has already been executed in this request
    }
    .... execute observer code

I know this answer is to late, but I hope will be usefull as I'm also having the same issue and able found a good solution.

I'm testing it using Magento 1.9 CE, in sales_quote_save_before observer, use following codes :

$quote = $observer->getEvent()->getQuote();
$quote->addErrorInfo('error', 'your_module_name', 1, 'your error message')->setHasError(true);

return $this;

This solution will also disable (remove) the checkout button in shopping cart page.