Investigate memory leak over time

[zadjii-msft]

From discussion in #745

I do not have very concrete data on it yet, but I also see a massive memory leak in WindowsTerminal.exe, even with only ever having just one tab open.
I tend to see this memory consumption happen most aggressively with any sort of application that continuously updates the screen like mtr or htop (I'm using the version of OpenSSH bundled with Windows build 18362 to connect to a Linux machine to run these). A session that run for just under 40 minutes got up to over 1000 MB of memory usage according to Task Manager.

Another bit of information, all that memory seems to be released over time, that same session, now sitting at a shell over SSH calms down and now roughly 3 hours later, it is using an efficient and trim 8.5 MB of RAM according to Task Manager.

[Robo210]

It looks like at least one stack that's doing constant allocations is

Commit Stack	Size (MB)
[Root]	3.609
ntdll.dll!RtlUserThreadStart	3.609
kernel32.dll!BaseThreadInitThunk	3.609
TerminalControl.dll!Microsoft::Console::Render::RenderThread::s_ThreadProc	3.609
TerminalControl.dll!Microsoft::Console::Render::Renderer::PaintFrame	3.609
TerminalControl.dll!Microsoft::Console::Render::Renderer::_PaintFrameForEngine	3.609
TerminalControl.dll!Microsoft::Console::Render::Renderer::_PaintBufferOutput	3.609
TerminalControl.dll!Microsoft::Console::Render::Renderer::_PaintBufferOutputHelper	3.609
TerminalControl.dll!Microsoft::Console::Render::DxEngine::PaintBufferLine	3.609
TerminalControl.dll!Microsoft::Console::Render::CustomTextLayout::_AnalyzeRuns	3.609
|- TerminalControl.dll!Microsoft::Console::Render::CustomTextLayout::_AnalyzeFontFallback	3.133
|    DWrite.dll!DWriteFontFallback::MapCharacters	3.133
|    DWrite.dll!FontFallback::MapCharacters	3.133
|    |- DWrite.dll!MatchFamilyToText	1.641
|    |- DWrite.dll!GetFontFamily	1.492

This came from 10 seconds of tracing while a progress bar was being printed to the console.

[Biswa96]

How did you find?