RFR: JDK-8186694: JShell: speed-up compilation by reusing compiler instances

[Jonathan Gibbons]

I don't think JavacTaskPool belongs in the javac.util package.

Unless there are good reasons for doing otherwise, how about using 
javac.api instead ... i..e closed to JavacTaskImpl and friend.

-- Jon


On 08/29/2017 12:58 PM, Jan Lahoda wrote:
> Hello,
>
> When starting jshell like this (where "/tmp/script" is a file which 
> has just "/exit"):
> $ jshell PRINTING --execution local /tmp/script
>
> It currently takes approx. 5-6s on my laptop. PRINTING will add quite 
> a few startup snippets. Each of these snippets is processed separately 
> and needs several instances of javac to be created to be processed 
> correctly.
>
> So, the idea in this patch is to reuse the javac instances multiple 
> (many) times. This avoids initializing the javac instances just to 
> process a very small ("single line") input.
>
> This patch is based on the ReusableContext by Maurizio used in tests. 
> The ReusableContext handling is wrapped in JavacTaskPool, which keeps 
> the ReusableContext and issues JavacTask possibly based on a reused 
> Context. The pool is not currently general purpose, but should work 
> for tests for which ReusableContext worked and for JShell.
>
> One tricky thing is that in JShell, it is necessary to prune 
> everything in the "REPL" package when reusing the Context, as it is 
> necessary to reload the correct/updated classes again from the file 
> manager (this is achieved by additional cleaning in TaskFactory).
>
> Overall, with this patch, the time to execute the above command is 
> approx. 2.5s
>
> Bug:
> https://bugs.openjdk.java.net/browse/JDK-8186694
>
> Webrev:
> http://cr.openjdk.java.net/~jlahoda/8186694/webrev.00/
>
> How does this look?
>
> Thanks,
>     Jan