[ws-proxy] Wait for workspace info until the request is canceled

[csweichel]

This PR makes ws-proxy wait for workspace info.
We wait for workspace info to arrive until the request context is canceled.

fixes #2299

How to test

Place a lot of load on the system, or artificially delay the ws-man subscription e.g. using blowtorch.

Also, there's a unit test :)

[akosyakov]

/werft run

👍 started the job as gitpod-build-cw-ws-proxy-wait-for-info.2

[geropl]

Started reviewing the code, will then have a closer look with blowtorch 👷‍♂️

[geropl]

Why not have the c.cond.Broadcast() here instead of in doInsert? It would help separate concerns (locking/notification) from insertion.

[csweichel]

I've moved here - and into Reinit - because then

• we don't signal that much during reinit (one broadcast after all insertions)
• the cond.Broadcast() is closer to the locking.

[geropl]

A comment on what the cond signal means. Here it's used as "some new info available" if I'm not mistaken (as opposed to "data has changed (added/removed)" as one might tempted to think).

[csweichel]

👍

[geropl]

A short comment would be ❤️

[csweichel]

👍

[geropl]

Do I understand correctly that we need this goroutine because we want to wait for - select - on a condition variable which is not selectable? And we use cond because we don't have the buffering problems and the cond code is nicer in the other places?

[csweichel]

Exactly, we have two things we want to wait for: context cancelation or info becoming available. We cannot select on the cond, hence need to "turn it into a channel". We use a cond because we have potentially multiple WaitFors waiting, and we cannot use a single channel directly (except with a much more complicated locked map).

[geropl]

I delayed ws-manager -> ws-proxy for several seconds. It always worked when the delay was <10s. Above, the workspace pod would start fine but the UI did hang in Starting.... This is expected as we 10s as the connection timeout between ws-proxy and ws-manager.

[geropl]

Cool! 🚀

(build fails bc gofmt only)