DispatchIO.read spinning while pipe is open on Windows

The sourcekit-lsp.exe consumes ~24% of CPU power all the time, even when idle. This bug does not appear under Linux, and does not appear in Swift versions earlier than v5.9. It is still present in v5.10. I tested this under VirtualBox, my virtual machine has 4 virtual processors. The host machine has 13th Gen Intel Core i7 processor, so ~24% load seems like a lot of mysterious calculations.

How to reproduce:

1. Install Swift version 5.9 .. 5.10. Install Microsoft VS Code and Swift extension for it (v1.8.1 from Swift Server Work Group).
2. Create a test Swift package:
   mkdir test
   cd test
   swift package init
3. Open the test folder in VS Code. (File | Open Folder...). At this point CPU usage increases, you don't even need to edit any source file. On my (usually silent) PC fan immediately starts rotating much faster, producing loud noise.
4. Check CPU usage by the sourcekit-lsp.exe: Press Ctrl-Shift-Esc, in the process list find the Visual Studio Code, click ">" next to it to see its sub-processes, and see high CPU usage by sourcekit-lsp .
5. Return to step 1 and this time install Swift version 5.8.1 or earlier. Repeat step 2 (create Swift package) because earlier version of Swift won't open a package created with a later version. Repeat all next steps and see ~0% CPU usage by sourcekit-lsp.exe .

This bug has nothing to do with VS Code. I found this bug when using my own app that runs sourcekit-lsp.exe, and not VS Code.

Start by reproducing the high CPU usage on Windows with Swift 5.9 or 5.10 and compare it with 5.8.1 or earlier. Trace the DispatchIO.read path while the pipe remains open, using the version difference and reproduction steps as the guide. Done means sourcekit-lsp.exe no longer spins while idle with the pipe open, with coverage for the regression if the relevant test location is found.