RFR: 8201274: Launch Single-File Source-Code Programs

Maurizio Cimadamore maurizio.cimadamore at oracle.com
Thu Apr 12 20:46:54 UTC 2018

Looks great - some initial comments (I can't really comment on the 
launcher changes):

* This logic is efficient:

int magic = (in.read() << 8) + in.read();
boolean shebang = magic == (('#' << 8) + '!');

but convoluted to read; perhaps could be improved slightly by making '#' 
<< 8) + '!' a static constant, and comparing against that.

* I note that the reading logic in general could be simplified, e.g. 
using Files.lines(Path) - but I assume that you wrote the code as is for 
performance reasons (e.g. to avoid creating too many string objects) ?

* I see that both the file manager and the class loader reasonably share 
the same context: a Map<String, byte[]>. I would make this more 
explicit, by having a Context class, whose state is the map, and then 
have the context provide two methods:


This way the sharing will be automatic, no need to extract one field 
from one place and pass it over to the other place.

* Big whohoo for being able to use the enhanced diagnostic framework 
with a couple of tweaks on the makefile - I hope that would have been 
the case when I put in the support, but since we have never done it - 
wasn't 100% sure it would work ;-)

Overall I like it quite a lot and I think you went for a really clean 
design - kudos!


On 12/04/18 21:15, Jonathan Gibbons wrote:
> Please review an initial implementation for the feature described in
> JEP 330: Launch Single-File Source-Code Programs.
> The work is described in the JEP and CSR, and falls into various parts:
>   * The part to handle the new command-line options is in the native
>     Java launcher code.
>   * The part to invoke the compiler and subsequently execute the code
>     found in the source file is in a new class in the jdk.compiler module.
>   * There are some minor Makefile changes, to add support for a new
>     resource file.
> There are no changes to javac itself.
> JEP: http://openjdk.java.net/jeps/330
> JBS: https://bugs.openjdk.java.net/browse/JDK-8201274
> CSR: https://bugs.openjdk.java.net/browse/JDK-8201275
> Webrev: http://cr.openjdk.java.net/~jjg/8201274/webrev.00/
> -- Jon

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