RFR: 8332084: Ensure JdkConsoleImpl.restoreEcho visibility in a shutdown hook [v4]

[Stuart Marks]

On Mon, 13 May 2024 21:32:18 GMT, Naoto Sato <naoto at openjdk.org> wrote:

>> Making sure `restoreEcho` correctly reflects the state in the shutdown thread, which differs from the application's thread that issues the `readPassword()` method.
>
> Naoto Sato has updated the pull request incrementally with one additional commit since the last revision:
> 
>   Addresses a review comment

I think we're assuming here that it's good practice for the Console to snapshot the initial tty state and to restore that state on exit. That's probably right.

If we're really supporting that, though, it means that the Console needs to be prepared to deal with whatever state the tty is in. In particular, if echo is off when the JVM starts, then we'll also need to make sure that ordinary reads turn echo on before actually reading.

And JLine probably also needs to do things like disable canonical input processing (stty -icanon, or "raw" mode, in Unix parlance). Will these be restored on exit? Hm... I just went and looked a bit through JLine, and it installs its own shutdown hooks! I didn't dig further to see exactly what they do though. Probably they're solving a similar problem though.

Unfortunately, shutdown hooks are unordered, so it's possible to that the shutdown hook added at this level will run either before or after JLine's and maybe they'll conflict. So maybe the SPI needs to have tty-save-state and tty-restore-state functions added to it, or something like that, so the responsibility for handling tty stated is pushed down to the provider. But I don't know if JLine could support that. The java.base provider might be able to do something reasonable though.

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PR Comment: https://git.openjdk.org/jdk/pull/19184#issuecomment-2110784011