[Lldb-commits] [lldb] [lldb-dap] Implement `runInTerminal` for Windows (PR #121269)

[Hu Jialun via lldb-commits]

SuibianP wrote:

The FIFO file served two purposes,
- Send real target PID back to debugger
- Synchronisation: Prevent premature execution of target

And the original implementation 0f0462c states the reason against socket and signal,

> I'm using this instead of using a signal or a similar mechanism because I don't want the launcher program to wait indefinitely to be attached in case the debugger crashed. That would pollute the process list with a lot of hanging processes.
> I preferred not to use sockets because it requires a lot of code and I only need a pid. It would also require a lot of code when windows support is implemented.

I took a step back and feel that this is probably doable without elaborate IPCs. Below is what I am thinking of (haven't actually tried yet).

1. Always create a new process in suspension (`SIGSTOP`/`CREATE_SUSPENDED`)
2. Send the PID back to debugger
    - POSIX, send signal and debugger can read `si_pid`
      - Dead launcher: timed `sigsuspend` with `alarm` (Darwin does not have `sigtimedwait`)
      - Dead debugger: `waitid(WNOHANG | WCONTINUED)` after timeout
    - Windows, use `PostThreadMessage` with `GetMessage`
      - Dead launcher: `MsgWaitForMultipleObjects`
      - Dead debugger: `CheckRemoteDebuggerPresent` after timeout
3. Attach to process and resume as normal

There would still be platform-specific code, but presumably still less clutter than FIFO/socket.

Any comments @ashgti @walter-erquinigo?

https://github.com/llvm/llvm-project/pull/121269