ConPTY: Fix a shutdown deadlock with WSL #16340
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Under normal circumstances this bug should be rare as far as I can observe it on my system. However, it does occur randomly. In short, WSL doesn't pass us anonymous pipes, but rather WSA sockets and those signal their graceful shutdown first before being closed later by returning a `lpNumberOfBytesRead` of 0 in the meantime. Additionally, `VtIo` synchronously pumps the input pipe to get the initial cursor position, but fails to check `_exitRequested`. And so even with the pipe handling fixed, `VtIo` will also deadlock, because it will never realize that `VtInputThread` is done reading. ## Validation Steps Performed * Build commit 376737e with this change and replace conhost with it Coincidentally it contains a bug (of as of yet unknown origin) due to which the initial cursor position loop in `VtIo` never completes. Thanks to this, we can easily provoke this issue. * Launch WSL in conhost and run an .exe inside it * Close the conhost window * Task manager shows that all conhost instances exit immediately (cherry picked from commit adb0472) Service-Card-Id: 91152102 Service-Version: 1.19
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Under normal circumstances this bug should be rare as far as I can
observe it on my system. However, it does occur randomly.
In short, WSL doesn't pass us anonymous pipes, but rather WSA sockets
and those signal their graceful shutdown first before being closed
later by returning a
lpNumberOfBytesReadof 0 in the meantime.Additionally,
VtIosynchronously pumps the input pipe to get theinitial cursor position, but fails to check
_exitRequested.And so even with the pipe handling fixed,
VtIowill also deadlock,because it will never realize that
VtInputThreadis done reading.Validation Steps Performed
Coincidentally it contains a bug (of as of yet unknown origin)
due to which the initial cursor position loop in
VtIonevercompletes. Thanks to this, we can easily provoke this issue.