如何通过访问会话信息超时会话并在超时前执行操作？

I am storing the items of shopping cart into a session array, but since the product ids and quantity is being stored on the client side , I can't perform a check on the quantity of items when a customer wants to add an item whose available quantity is already added to other customers carts.

So I have added a column called added_to_cart in my Products table which increments when a product/item is added to a customers session cart.

Now I want to time out the session when there's no activity by the customer for an hour and decrement the added_to_cart by checking what's stored in the inactive(to be timed out)php session

    Products
    -----------------------------------------
    : p_id  : available_qty : added_to_cart :
    -----------------------------------------
    : p-123 :  57           : 3             :
    -----------------------------------------
    : p-287 :  32           : 8             :
    -----------------------------------------

1.Is it possible to do it when the customer doesn't visit the site ever after(i.e without calling the session_start()).If so how?.

2.Is it the right proposed solution?How do they do it in bigger online stored like amazon and ebay?

You should do the FINAL quantity check when order is placed/submitted, not when added to cart. Think what happens, if somebody adds all products in your system to cart (just for fun).. your eCommerce shop would be sold out :)

So should be like:

  • when viewing item available quantity (in stock quantity) use value from database (real, current, available quantity)
  • when order is submitted, check that the quantity ordered is available. If not, notify user. If is, make the reduction and save to DB.

There is also lot of well maid, free eCommerce softwares available like: Magento (http://magento.com/)

TIMED SESSIONS:

But if you really want to do the session thing, you can:

  • save sessions to database with timestamp
  • update timestamp on every page request by user (like "last access")
  • periodically delete old session rows and "free" reserved products

Keep in mind that the sessions (reserved products related) should then be quite short (like 30 minutes?).