RFR: JDK-8202105: jshell tool: on exiting, terminal echo is disabled

Martin Buchholz martinrb at google.com
Wed Apr 25 19:07:29 UTC 2018

I keep hoping for something simpler.

Is it possible to have more than one Console object?  Looks like NO.
Assuming no, then you simply need one static flag

boolean restoreEcho;

(it could also be an instance field of Console - that would be slightly
more principled)

In readPassword you check current value of echo and set restoreEcho if it
was changed.  Shutdown hook also checks the same restoreEcho.

For bonus points, only create the shutdown hook the first time readPassword
is called with echo on to appease the Emacs shell users with pitchforks.

On Wed, Apr 25, 2018 at 9:34 AM, Xueming Shen <xueming.shen at oracle.com>

> On 4/25/18, 9:02 AM, Martin Buchholz wrote:
> It would be more correct I think for Console to track if there is a
> pending readPassword in progress and try to restore echo on exit only if
> so.  But a little annoying to implement (need an additional boolean?)
> I think that is what Jan proposed "to add restoredEchoOnShutdown = true",
> and I'm fine
> with that. I'm just a little confused why jshell invokes System.console()
> if it handles all "raw"
> terminal stuff itself.
> On Wed, Apr 25, 2018 at 8:52 AM, Xueming Shen <xueming.shen at oracle.com>
> wrote:
>> Hi Jan,
>> I saw System.console() returns null inside jshell ... but it seems there
>> are 2 vms.
>> I would assume jshell  itself sets the terminal to raw and then call
>> System.console()?
>> for example an alternative for this issue is to ask jshell's impl to call
>> System.console()
>> before going into raw mode? No, I'm not saying the proposed one is not a
>> good one,
>> just wanted to make sure I understand the situation correctly.
>> Thanks,
>> Sherman
>> On 4/25/18, 4:50 AM, Jan Lahoda wrote:
>>> Hi,
>>> Under:
>>> https://bugs.openjdk.java.net/browse/JDK-8194750
>>> j.i.Console was changed to capture the state of the terminal echo at
>>> creation time, and to restore it on shutdown.
>>> That is problematic at least in jshell, where the terminal is already in
>>> the raw mode when j.i.Console is created, and so "echo disabled" is
>>> recorded there. So even though jshell itself sets the terminal into the
>>> original mode when it terminates, the shutdown hook in j.i.Console, which
>>> is run later, sets the echo to off even if it was enabled before the VM
>>> started.
>>> My understanding is that the shutdown hook is only needed in case the VM
>>> goes down while readPassword is running. So I tried to change the shutdown
>>> hook to only work while readPassword is running.
>>> Bug: https://bugs.openjdk.java.net/browse/JDK-8202105
>>> Webrev: http://cr.openjdk.java.net/~jlahoda/8202105/webrev.00/
>>> What do you think?
>>> Thanks,
>>>     Jan

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