/sync stops working when the tab becomes inactive

[turt2live]

The system is not constrained for resources, and Chrome looks happy. Might have something to do with switching to browserified request

[turt2live]

information dump time:

This is a regression introduced by matrix-org/matrix-js-sdk#764. Something in request uses an API that Chrome suspends alongside the tab, which causes requests to freeze. Bringing the tab back into the foreground fixes the issue by making a large sync.

This particular bug is only noticeable on larger accounts due to resource consumption (probably). Chrome, and other browsers, will forcefully pause some APIs (like timers) when the tab is not in the foreground. This is usually only invoked when the process is using a lot of resources or the system is otherwise strained for resources. In my case, the system is not strained for resources however my account appears to be just past the tipping point for Chrome to pause things. This is why smaller accounts probably won't see the problem at all.

Switching request back to browser-request does resolve the issue, however that would break joining rooms with multiple server names (now a feature of the js-sdk). The API that is being paused is probably being used by the http shim (https://github.com/jhiesey/stream-http) or by request itself. Both APIs are relatively small, so it may be feasible to continue trying to walk through and find the problem.

Neither repository appears to have an issue already open for this. Then again, we might be the first to have a high resource usage app which also uses request browserified.

There's a few ways forward on this issue:

1. Identify and fix whatever API is being paused.
2. Switch to browser-request for the majority of APIs, using request for joining rooms.
3. Make Riot not use so much memory

Option 1 is probably the best option given 2 is just a hack and 3 is wildly out of scope.

[turt2live]

Fixed by matrix-org/matrix-js-sdk#770. Future maintenance recorded at #7634.