3 ms·

When I was a kid we had vending machines for drinks in school. One morning I put 20p in and it immediately came back out. It wasn’t accepting the coin so I tri

When I was a kid we had vending machines for drinks in school. One morning I put 20p in and it immediately came back out. It wasn’t accepting the coin so I tried two in quick succession. Both were spat back out… but the machine registered one of them. I of course would never exploit that repeatedly for a couple free drinks and some extra change too.

hamburglar 4y ago
The soda machine in my dorm at college had separate mechanisms for “I released a soda” and “you actually got a soda” and if you knew this, you could trigger the “I released a soda” mechanism and delay the “you actually got a soda” event until after you got your money back. You just had to stick your arm up the machine and not let the released soda fall while you hit the cancel button. Then you got your money back and then a soda. Atomicity fail.
- wildzzz 4y ago
  They were not around for very long but there was a soda machine that had a conveyor belt that drinks would drop down onto and then be pushed out of a flap door into the bucket. The machine could detect when a drink was actually vended but didn't seem to be able to detect when someone was holding the door shut. You'd pay for a drink and hold the door shut while the machine tried to push your drink out the door. Since the door wasn't opening, the machine would think that no drink ever dropped down onto the conveyor belt so it would mark that specific drink number as out of stock and return your money. Except your drink selection was still sitting on the belt. You'd pick a new drink and pay for it but this time not holding the door shut, two drinks would come out for the price of one. You could do this quite a few times over to either get a couple free drinks or just jam the machine. Out of all the vending machine "hacks" I learned about in middle school, this was the only thing that ever worked and only for a short time before they got quickly replaced. The new machines use either a basket to hold the drink instead of a conveyor belt or some sort of shield to prevent you from messing with the flap door until it knows a drink has been vended.
- woah 4y ago
  Seems like it was working as intended, that if there was some blockage in the machine that resulted in the soda getting released but then getting stuck, you'd want a refund.
  - hamburglar 4y ago
    Somehow I doubt giving out unlimited free sodas is "as intended." This is why it's an atomicity fail, leading to an inconsistent transaction. It should never be blocked according to the payment mechanism and unblocked according to the delivery mechanism.
    - woah 4y ago
      No it's literally just a good faith effort to err on the side of customer satisfaction being exploited to steal a soda.
philjohn 4y ago
The tumble dryers in my halls of residence were meant to take 20p (oh, those were the days, it's probably a quid now), but if you put in a 1p slowly and kept turning the handle it would trick it.

hamburglar 4y ago

The soda machine in my dorm at college had separate mechanisms for “I released a soda” and “you actually got a soda” and if you knew this, you could trigger the “I released a soda” mechanism and delay the “you actually got a soda” event until after you got your money back. You just had to stick your arm up the machine and not let the released soda fall while you hit the cancel button. Then you got your money back and then a soda. Atomicity fail.

wildzzz 4y ago
They were not around for very long but there was a soda machine that had a conveyor belt that drinks would drop down onto and then be pushed out of a flap door into the bucket. The machine could detect when a drink was actually vended but didn't seem to be able to detect when someone was holding the door shut. You'd pay for a drink and hold the door shut while the machine tried to push your drink out the door. Since the door wasn't opening, the machine would think that no drink ever dropped down onto the conveyor belt so it would mark that specific drink number as out of stock and return your money. Except your drink selection was still sitting on the belt. You'd pick a new drink and pay for it but this time not holding the door shut, two drinks would come out for the price of one. You could do this quite a few times over to either get a couple free drinks or just jam the machine. Out of all the vending machine "hacks" I learned about in middle school, this was the only thing that ever worked and only for a short time before they got quickly replaced. The new machines use either a basket to hold the drink instead of a conveyor belt or some sort of shield to prevent you from messing with the flap door until it knows a drink has been vended.
woah 4y ago
Seems like it was working as intended, that if there was some blockage in the machine that resulted in the soda getting released but then getting stuck, you'd want a refund.
- hamburglar 4y ago
  Somehow I doubt giving out unlimited free sodas is "as intended." This is why it's an atomicity fail, leading to an inconsistent transaction. It should never be blocked according to the payment mechanism and unblocked according to the delivery mechanism.
  - woah 4y ago
    No it's literally just a good faith effort to err on the side of customer satisfaction being exploited to steal a soda.

philjohn 4y ago

The tumble dryers in my halls of residence were meant to take 20p (oh, those were the days, it's probably a quid now), but if you put in a 1p slowly and kept turning the handle it would trick it.