In gapir we're now getting frequent assertions:

Assertion failed: (NSViewIsCurrentlyBuildingLayerTreeForDisplay() != currentlyBuildingLayerTree), function NSViewSetCurrentlyBuildingLayerTreeForDisplay, file /BuildRoot/Library/Caches/com.apple.xbs/Sources/AppKit/AppKit-1561.20.106/AppKit.subproj/NSView.m, line 14480

Seems to have appeared when my machine update to High Sierra, which seems to be a common theme with others that have reported this assertion:

Swordfish90/cool-retro-term#374
https://forum.silicondust.com/forum/viewtopic.php?t=66156
https://forums.developer.apple.com/thread/91712

There's also a lot of mentions of multi-threaded code - so perhaps there's some framework code that needs to be kept on the same thread.