I have a question about the situation which arises during the flash sale in e-commerce websites. Assume there are only 5 items in stock and if 10000 requests hit the server at same instant, how does the server handle the requests and how does it manage to order the request?
Given the cpu speeds of current computers, like it says here
1 million requests per second, would come out as 1 request per 1000 cpu cycles.
Although requests come from many ends of the world, they are received through a single channel. Which means that two requests come after one another even if they are originated at the exact same time. The time of receipt would certainly not be the same, if routing conditions for the two requests are considered. It is impossible for them to hit the server at the exact same time. Because routing wouldn't allow it in order to prevent collisions.
Therefore the order in which the requests are handled is the order they are received at the network interface. After the request packets are through the application layer, each client will have a thread dedicated for itself. But the access of shared variables like the 5 items you mentioned will be synchronized. Therefore only the first 5 threads to acquire the lock on these shared variable will win.