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

[Jan Lahoda]

So, if I understand correctly, it would be:
boolean flipEcho;
and the readPassword would do something like:
if (echo0() != false) {
     flipEcho = true;
     echo(false);
}
....
if (flipEcho) { //this would also be in the shutdown hook
      echo(!echo0());
}

I guess I can do that (the variant with two boolean feels to me slightly 
easier to understand and a tiny bit more robust, but this flip boolean 
variant is doable as well).

Thanks,
     Jan

On 25.4.2018 21:07, Martin Buchholz wrote:
> 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>
> wrote:
>
>> 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
>>>>
>>>
>>>
>>
>>