Performance / JShell lightweight

[Christian Stein]

Slightly off-topic, but related: That local execution mode allows to "/exit
1" via "System.exit(1)".

Like wished/requested here http://mail.openjdk.java.
net/pipermail/kulla-dev/2017-August/002063.html

Little proof of concept runnig on a DOS shell:

jshell --execution local
|  Welcome to JShell -- Version 9
|  For an introduction type: /help intro

jshell> System.exit(123)

echo Exit Code is %errorlevel%
Exit Code is 123

On Mon, Aug 14, 2017 at 11:27 PM, Robert Field <robert.field at oracle.com>
wrote:

> Yes, most of the time is spent in launching/setting-up the remote VM.
>
> You can get local execution with:
>
>     jshell --execution local
>
> This has downsides, for example if the executed code crashes/exits, so
> does the shell.
>
> This is kinda documented in:
>
>     jshell -X
>
> and the SPI/API:
>
> http://download.java.net/java/jdk9/docs/api/jdk/jshell/spi/p
> ackage-summary.html
> http://download.java.net/java/jdk9/docs/api/jdk/jshell/execu
> tion/package-summary.html
>
> As to exiting a script, in general, simply use the "exit" command.
>
> -Robert
>
>
> On 08/14/17 13:33, Remi Forax wrote:
>
>> Hi Robert,
>>
>> It's due to the fact that by default JShell starts a new VM (the remote
>> VM) that will execute the code,
>> if you just want to run the code, i think there is a way to run the
>> script inside the same VM.
>>
>> I will let the other Robert (Field) or anyone on this list explain how to
>> do this,
>> i'm also interested by the answer (and the auto-exit at the end).
>>
>> cheers,
>> Rémi
>>
>> ----- Mail original -----
>>
>>> De: "Robert Scholte" <rfscholte at apache.org>
>>> À: kulla-dev at openjdk.java.net
>>> Envoyé: Lundi 14 Août 2017 22:24:25
>>> Objet: Performance / JShell lightweight
>>> Hi,
>>>
>>> I've started a library which has the ability to divide a set of jars and
>>> output directories over the classpath and modulepath. In order to get the
>>> modulename it calls the Java 9 code for retrieving that name, i.e. via
>>> ModuleFinder.
>>> In case the library runs on Java 9, it can call the ModuleFinder
>>> directly.
>>> But in case the library runs on Java 7 or Java 8, it requires a reference
>>> to the Java 9 home.
>>> With JShell it has become very easy to execute this code, otherwise I
>>> need
>>> to have an executable-jar at runtime, put is somewhere where I can call
>>> it.
>>>
>>> However, this call to JShell takes several seconds to resolve, which
>>> feels
>>> quite long. I'm looking for a way to reduce this time.
>>>
>>> I'm not interested in interaction with JShell, only interested in the
>>> output. (in the end it is almost as simple as a main method with
>>> System.out.println("Hello World"); )
>>>
>>> If the startup overhead is caused by building up the shell, can there be
>>> an option introduced to just execute code without interactive shell (and
>>> auto-exit at the end)?
>>>
>>> thanks,
>>> Robert
>>>
>>
>