Conpty: Terminal rendering very slow with huge output

[GoaLitiuM]

Conpty renders terminal window almost unusable when a compiler suddenly emits hundreds of hundreds of error lines.

For example, running tree /F in my dev folder took this long to finish:

• ~12sec in Command Prompt
• ~11sec in VSCode without Conpty
• ~65sec in VSCode with Conpty

Renderer type has minor difference to the execution speed where DOM being slightly slower, but these were observed with Canvas rendering enabled.

Steps to Reproduce:

1. Enable Conpty.
2. Run a command which produces lots of lines (like tree C: /F)
3. Repeat without Conpty and observe how much longer it takes to finish the command.

• VSCode Version: 1.39.2
• OS Version: Windows 10 build 18362

Does this issue occur when all extensions are disabled?: Yes

[vscodebot]

(Experimental duplicate detection)
Thanks for submitting this issue. Please also check if it is already covered by an existing one, like:

• terminal.integrated.windowsEnableConpty is not being respected (#84082)

[Tyriar]

Speed should improve somewhat in 1.40 but the root cause of this is #74620

/duplicate

[GoaLitiuM]

Confirmed, 1.40 has similar performance between those two modes. Thanks.