[foreign] RFR 8211060: Library.getDefault() does not work on Windows

[Maurizio Cimadamore]

Hi Jorn,
thanks for the patch. As mentioned last time we have two options here: 
one is to follow the approach forward in your patch; another would be to 
ditch Library.getDefault() entirely and adopt a more explicit approach - 
that is to always require 'implicit' libraries to be mentioned - either 
by jextract artifacts or by API points.

A note on the latter - when you do:

Libraries.bindRaw(lookup, Foo.class)

the code lookup the @NativeHeader annotation on Foo.class and tries to 
extract required library names from there. Currently, we do not add 
library names for standard libraries such as "c" or "m" (math), which is 
what led us down the (slippery?) slope of having a Library.getDefault 
somewhere.

Another option would be to have jextract to always generate the names of 
the libraries an artifact depends on, and then the API should throw an 
exception if a @NativeHeader is found with no libraries. More 
specifically, jextract should always add "c" to the set of used 
libraries in the @NativeHeader annotation (other libraries can be 
explicitly supplied using the -l flag).

Note that I'm not saying "the binder should always add in 'clib'" for 
you, because that's kind of a lame assumption: it works obviously well 
for C but it doesn't make a lot of sense if you want to use Panama for 
other purposes/languages. Which seems to suggest that, as far as the 
binder is concerned, library dependencies should always be explicit.

Thoughts?

Maurizio



On 24/09/18 11:52, Jorn Vernee wrote:
> Hello,
>
> I'd like to contribute a patch that adds support for the default 
> library on windows.
>
> Bug: https://bugs.openjdk.java.net/browse/JDK-8211060
> Diff: https://gist.github.com/JornVernee/7d45780df082cbfb27417b437c7b13a8
>
> As mentioned before [1], this fixes 2 bugs:
>
> 1.) When no library was loaded ClassLoader#NativeLibrary#getFromClass
> threw an NPE (at least on windows). That is fixed by returning
> defaultLibrary.fromClass when the nativeLibraryContext is empty.
>
> 2.) The default library search was not working on windows. It was using
> a default handle, which works on unix (dlsym(RTLD_DEFAULT)), but not on
> windows (see https://stackoverflow.com/q/23437007). I have changed the
> implementation from using a default handle to using a new native
> function findEntryInProcess, which does the right thing for Windows
> (iterate over all loaded modules), and does the same thing it used to
> for unix. findEntry is now a Java method, and the original findEntry is
> renamed to findEntry0. The NativeLibrary implementation of findEntry
> forwards to findEntry0, and the anonymous class of the default library
> overrides to forward to findEntryInProcess.
>
> Please test this patch on unix as well, since I don't have the ability 
> to do so.
>
> Jorn
>
> [1] : 
> http://mail.openjdk.java.net/pipermail/panama-dev/2018-September/002644.html