[1.19] Random lags on focus and unfocus

[lhecker]

Windows Terminal version

1.19.2682.0

Windows build number

No response

Other Software

No response

Steps to reproduce

• Run rainbowbench -ng
• Focus and unfocus the application

Expected Behavior

rainbowbench should show something along the lines of

22486 fps | 83132 kcg/s

or about half that on a slower CPU.

Focusing/Unfocusing doesn't randomly lag the renderer.

Actual Behavior

7436 fps | 26605 kcg/s

and it randomly lags.

[lhecker]

The throughput issue occurs because I now flush a ConPTY frame whenever DoWriteConsole returns. Previously, ConPTY would only flush it after up to 16.7ms when the next rendering iteration occurs. I think this is fine, because I'd like to move away from the asynchronous nature of ConPTY over to a direct translation.

I can't quite figure out why I had lags though. It's been gone ever since I disabled G-SYNC and it hasn't come back even after enabling G-SYNC. Weird.

[zadjii-msft]

This seems related to #12336, but not exactly the same.

Hypothesis: we should stop WriteFileing in EndPaint, because that blocks the I/O thread until ConPtyConnection ReadFiles ((baseless assumption))