RE: trySetAccessible​

[Uwe Schindler]

Hi Alan,

I was trying to fix Groovy to use trySetAccessible() instead of setAccessible() and this did not change any warnings at all: The code can be found here:

https://github.com/apache/groovy/compare/master...uschindler:java9/trySetAccessible

It did not change anything. In fact, the code behaved as it did before - no change at all! Warnings are almost the same (actually worse, because of how I did it using MethodHandles, see bwlow). It also granted full access, like the usual call to setAccessible()!

As Jochen said: 

> Now I am told those warnings appear here as well.

I was the one who told it to him indirectly... because I tried to fix it for Groovy with the above code change!

It granted access to internal API as it did before and it also printed the warning - so the new API was identicak to a simple call to setAccessible. Why is the new AI there at all, setAccessible did the same. And an if/then/else vs. a try/catch is not really different! Sorry, I expected trySetAccesible() to behave differently: As this is a *new* API in Java 9, I would have expected that the "big kill switch" does not affect this! So when calling this new API, I would have expected that it would behave as follows:

- It would *not* grant access to internal APIs, as specified in the Java 9 spec and the module system. As the API is new, there s no need for it to respect the "big kill switch" aka "permit-illegal-access".
- It would not print a warning at all!

In fact the new code in the above patch to Groovy was much more confusing, as the warning was suddenly printed by a JDK-internal class - which is a bug IMHO: The JDK printed a warning like this:

WARNING: An illegal reflective access operation has occurred
WARNING: Illegal reflective access by org.codehaus.groovy.reflection.InjectedInvoker/1364880320 (file:/C:/Users/Uwe%20Schindler/Projects/groovy/target/classes/java/main/) to method java.lang.Object.finalize()
WARNING: Please consider reporting this to the maintainers of org.codehaus.groovy.reflection.InjectedInvoker/1364880320
WARNING: Use --illegal-access=warn to enable warnings of further illegal reflective access operations
WARNING: All illegal access operations will be denied in a future release

This came from the fact, that the internal wrapper of the MethodHandle, which was created by the call to trySetAccessible() using a MethodHandle. I suppose it was used to make the caller-sensitive stuff work correctly. So I was baffled, because the warning was not really helpful anymore! The class mentioned here does not even exist anywhere!!! ☹

Uwe

-----
Uwe Schindler
uschindler at apache.org 
ASF Member, Apache Lucene PMC / Committer
Bremen, Germany
http://lucene.apache.org/

> -----Original Message-----
> From: jigsaw-dev [mailto:jigsaw-dev-bounces at openjdk.java.net] On Behalf
> Of Alan Bateman
> Sent: Monday, July 10, 2017 10:07 AM
> To: Jochen Theodorou <blackdrag at gmx.org>; jigsaw-dev at openjdk.java.net
> Subject: Re: trySetAccessible​
> 
> On 10/07/2017 00:16, Jochen Theodorou wrote:
> > Hi all,
> >
> > since the JVM now prints warnings if you call setAccssible there was
> > the advise to move to trySetAccessible​ to prvent these warnings.
> The motivation for trySetAccessible is to avoid using exceptions for
> control flow. I don't recall any suggestion here to use it as a way to
> avoid warnings.
> 
> Remember the purpose of the warnings is to make you or your users aware
> that the code will behave differently when access to JDK internals, or
> other so-called illegal access, is denied.
> 
> -Alan