1.18+: IPC stopped sharing instaces by default?

[KarelPeeters]

Since version 1.18 it seems that when launching tev for the second time it does not properly connect to the existing instance any more.

For example:

I launched tev in the left terminal first, which opened a new window as expected. Then I launched tev in the second terminal, it says it's connecting to the primary instance (which the left terminal confirms) but then still opens its own window.

I get the same issue on the 1.18, 1.19 and 1.20 released exe files, on 1.17 everything works as normal.

Did the behavior intentionally change? I checked the change-logs but couldn't really find anything.

[Tom94]

Hi there, yes, this behavior is intentional: opening tev without any image arguments spawns a new window now (to allow people to open multiple instances side-by-side without passing images first). I think this is more intuitive than making $ tev a no-op if a window is already open.

That said, I hadn't considered the use-case of someone wanting to either open a tev render window or reusing an existing one if it's already there. I'll modify the CLI shortly to give you the option to revert to old behavior.

[Tom94]

(Extra background info: the IPC connection that you see in your console logs is intentional. Even when multiple windows of tev are open side-by-side, there is still only a single "primary" window that receives IPC data. When this window gets closed, one of the secondary windows automatically promotes itself to become the new primary.)

[KarelPeeters]

Ah I see, that all makes sense but getting the old behavior back as an option would be very useful.

Could you elaborate on how the handover works when the primary window closes? I assume the original TCP socket still gets closed, and another instance opens a new one? Doesn't that kill exiting connections?

[Tom94]

Yeah, the TCP socket gets closed, existing connections are killed, and the first secondary instance that manages becomes a new host that listens on the same port.

Given that the new host is a genuinely different tev instance with different images & state, I think the reset of the connection makes more sense than trying to keep the existing connection alive.

[Tom94]

Of note: the intended function of this is that a subsequent $ tev image.exr doesn't spawn a new window if there are still existing ones -- i.e. as long as at least one instance of tev is running, one of them will handle IPC traffic.

As a corollary: the whole discussion concerns multiple tev instances that are bound to the same ip/port. If you were to spawn one regular tev instance and another via $ tev --host 127.0.0.1:1337, the second one would be its own independent primary instance.

[KarelPeeters]

Great, thanks a lot for explaining and the new flag!