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

Samuel Audet samuel.audet at gmail.com
Mon Sep 24 11:38:36 UTC 2018

FWIW, I think the factory method pattern should be reconsidered 
entirely. In C/C++, when we want to call say getpid(), we don't start 
loading stuff up before calling getpid(), we call getpid()! Why not do 
the same from Java? From a usability point of view, not loading stuff 
manually works fine for JavaCPP...

Now, I know you're going to start taking about interfaces and what not. 
You said that you had plans to introduce an entirely new array type just 
to make it more friendly with vector instructions and native libraries. 
Why not start thinking about an "interface" that would be friendly to 
native libraries as well? Why stop at arrays?


On 09/24/2018 08:10 PM, Maurizio Cimadamore wrote:
> 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 

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