We are trying to enable collaborative chats in an educational application. The general idea is that the users (students) will start an exercise, this will make them join an specific waiting room. And somehow the system should be able to decide it has enough students to create a group of n students (depending on the exercise) according to a given strategy and will send a message to those students to join a chatroom with a generated ID so that they can collaborate.

Right now we are totally blank and cannot decide on how to make the server decide wether to try and create groups or to wait for more students. Our stack is in Spring Boot, Redis and Postgress. Our initial idea was to add the students into a waiting room in Redis and launch a Spring event every time a student joined the waitlist. However, we understand that approach might generate many race conditions, which should be avoided.

CodePudding user response：

Create an exercise_students table which has a SERIAL column on it, call it arrival_order or something. Another column for group_id. As students sign in for the exercise, insert them into this table. By nature SERIAL is atomically auto-incremented, so you avoid race conditions. Regularly query the table for students with no group_id (I assume you have a exercise_group table of some sort that defines how many students are part of a group). When the count reaches n, update them with the group_id and create a new group in the exercise_group table for the next group.

Relational databases are pretty good at this sort of thing. Atomic updating of state is pretty straightforward stuff.