With the work on Gamefinder 2.0 progressing well and us just pushing a test version for people to play with to the site, I figured I'd bring back this blog topic with a description of a complicated problem and how it's being addressed in the new Gamefinder.

For a while, we've had recurring instances of people being scheduled to two games at the same time with the current game finder. It's not super common, but it does happen and wastes a bit of time for coaches and staff alike. It took quite a long time to figure out why this happens and how, and it has to do with a complex internal state of the game finder system. I'll give a high-level explanation of what the gamefinder does and how it functions, and then go into the bug itself.

The gamefinder system maintains a list of "possible matches", and an internal state for each match saying which coach has done what. There is a "two step" accept sequence, where both coaches first need to "accept" a match, and then once both coaches accepted, they both need to "start". This is done like this because of how the system allows multiple offers to be sent at any given time (funnily enough, this is the main way to guard against a coach being scheduled against multiple opponents).

So in a sense, a match goes from "Default" to "Accepted" to "Started" with both coaches involved needing to accept or start to push the match forward in the sequence.

Now, the bug relates to the "half started" state, where only one coach has clicked the start button. Essentially, if a coach clicks to start, and the opponent doesn't, the game will time out after a while and "release" both coaches. However, if a coach clicks to start, and then decides it's taking too long and simply reloads the page, there will be a pending match to start and the original coach will have no feedback.

If the opponent also clicks start after the original coach reloaded the page (which took them to the start page for the gamefinder), the match will be scheduled and the opponent will be launched into the game. At this point, the original coach doesn't get the information and can schedule a second game at the same time, unaware of the first one.

As a corollary to this, there is a case where, because of the multi-offer feature, coaches can get a dialog to start a match while the opponent is responding to another match. In certain situations, this could cause a second start dialog to show up almost immediately after the first one has been resolved which could appear as if the start button didn't work and the coach just clicks again without noticing that it's another game.

With Gamefinder 2.0, I wanted this to not be possible, and what we've done is something that is not really visible to coaches unless you look really carefully

In addition to maintaining the matches and their internal state (which works largely in the same way), the system also maintains a list of "start dialogs", which have their own states as well. They can be either "active", which shows the match start dialog to both coaches for a given pairing, or "inactive" which means that one of the coaches is already responding to a dialog for another game. For a typical coach, this will show up as a delay between clicking to accept a match offer and the start dialog showing up.

If the opponent clicks to start the other game, however, all other matches for that coach will be cancelled and the offer will disappear from view (just as if they clicked to cancel it).

In addition to maintaining this list of start dialogs, the system will also automatically re-show the dialog if a coach reloads the page. To "cancel", we've also added an explicit button for this which will allow coaches to change their minds and move on to find another game without having to wait for the full timeout.

This was an interesting problem to solve, and I wanted to share how it was dealt with because it feels fairly elegant and will hopefully resolve the issues we've had in the past with this.