RFR: 8238080: FXMLLoader: if script engines implement javax.script.Compilable compile scripts

[Rony G.Flatscher]

On Tue, 12 May 2020 17:33:06 GMT, Rony G. Flatscher <github.com+60214806+ronyfla at openjdk.org> wrote:

>> Suggested CSR:
>> 
>> Summary
>> =======
>> Have javafx.fxml.FXMLLoader compile FXML scripts before evaluating them, if the script engine
>> implements the javax.script.Compilable interface to speed up execution. In case compilation
>> throws a javax.script.ScriptException fall back to evaluating the uncompiled script. Allow
>> control of script compilation with a "compile" PI for FXML files.
>> 
>> Problem
>> =======
>> javafx.fxml.FXMLLoader is able to execute scripts in Java script languages
>> (javax.script.ScriptEngine implementations) referred to or embedded in a FXML file.
>> 
>> If a script engine implements the javax.script.Compilable interface, then such scripts could be
>> compiled and the resulting javax.script.CompiledScript could be executed instead using its
>> eval() methods.
>> 
>> Evaluating the javax.script.CompiledScript objects may help speed up the execution of script
>> invocations, especially for scripts defined for event attributes in FXML elements (e.g. like
>> onMouseMove) which may be repetitively invoked and evaluated.
>> 
>> Solution
>> ========
>> Before evaluating the script code test whether the javax.script.ScriptEngine implements
>> javax.script.Compilable. If so, compile the script to a javax.script.CompiledScript object first
>> and then use its eval() method to evaluate the script, otherwise continue to use the
>> javax.script.ScriptEngine's eval() method instead. Should compilation of a script yield
>> (unexpectedly) a javax.script.ScriptException then fall back to using the
>> javax.script.ScriptEngine's eval() method. A new process instruction "compile" allows control of
>> the compilation of scripts ("true" sets compilation on, "false" to set compilation off) in FXML
>> files.
>> 
>> Specification
>> =============
>> If a javax.script.ScriptEngine implements the javax.script.Compilable interface, then use its
>> compile() method to compile the script to a javax.script.CompiledScript object and use its
>> eval() method to run the script. In the case that the compilation throws (unexpectedly) a
>> javax.script.ScriptException log a warning and fall back to using the
>> javax.script.ScriptEngine's eval() method instead.
>> To allow setting this feature off and on while processing the FXML file a "compile" process
>> instruction ("<?compile false?>" or "<?compile true?>") gets defined that allows to turn
>> compilation off and on throughout a FXML file.
>
> Doc addition for the CSR:
> =================
> The following text was added to the [Introduction to
> FXML](https://github.com/openjdk/jfx/blob/master/modules/javafx.fxml/src/main/docs/javafx/fxml/doc-files/introduction_to_fxml.html)
> at two locations, the "Script Event Handlers" ("#script_event_handlers") and the "Scripting" (#scripting") sections:
>> <p>Hint: to turn off automatic compilation of script code place the processing instruction <span
>> class="code"><?compile false?></span> before the script. To turn on compilation of script code again use the
>> processing instruction <span class="code"><?compile true?></span> (or short: <span
>> class="code"><?compile?></span>). The compile processing instruction can be used repeatedly to turn compilation
>> of script code off and on.</p>
> 
> This documents the compile processing instruction, that it compilation is on by default and that it can be turned off
> and on repeatedly. It is hoped that this formulation plays well with the context where this paragraph got introduced.

Doc addition for the CSR (update)
-------------------------------------
In the event handler section:
> <p>Note: to turn off automatic compilation of script code place the processing instruction <span
> class="code"><?compile false?></span> before the element that contains the script. To turn on compilation of
> script code again use the processing instruction <span class="code"><?compile true?></span> (or short: <span
> class="code"><?compile?></span>). The compile processing instruction can be used repeatedly to turn compilation
> of script code off and on.</p>

In the Scripting section:
> <p>Note: to turn off automatic compilation of script code place the processing instruction <span
> class="code"><?compile false?></span> before the script element. To turn on compilation of script code again use
> the processing instruction <span class="code"><?compile true?></span> (or short: <span
> class="code"><?compile?></span>). The compile processing instruction can be used repeatedly to turn compilation
> of script code off and on.</p>

-------------

PR: https://git.openjdk.java.net/jfx/pull/192