How to check if Configurable Product is out of stock?

if (!$configurable->isSaleable() ||$configurable_product->getIsInStock()==0){
// out of stock
}

For checking child simple product:

$allProducts = $configurable->getTypeInstance(true)
                ->getUsedProducts(null, $configurable);
            foreach ($allProducts as $product) {
                if (!$product->isSaleable()|| $product->getIsInStock()==0) {
                    //out of stock for check child simple product
                }
            }