What the circumstances were.
Starting a new colony
What happened.
Switching away and then back in fullscreen mode hung rimworld
What you expected to happen.
It wouldn't hang, and would keep running in the background (or at worst pause)
Steps we can follow to make the bug appear on our machine. This part is important! We need a set of steps which we can follow to get the same results you're seeing. Ideally you'll test these steps to make sure they work from scratch.
Install gentoo linux
Install steam
Install rimworld
Set full screen
Start a colony, 100 percent globe fill
While it's generating, switch windows with alt-tab
Repeat until rimworld hangs
Observe via a process monitor that CPU usage for rimworld hits zero.
This also happens often when alt-tabbing during an actual running game.
My resolution is 1024x768 and I have an i7 CPU with intel graphics drivers if it helps.
Savegame file
It's very helpful to include a savegame, especially when you have trouble reproducing the bug.
N/A, it happened before the colony was created
Other information:
I used GDB once, it seems to be hanging on a futex?