Null Callbacks

[Jorn Vernee]

Sorry to hear that. I think the Libraries.bind trick only works if there 
is a free function in the same interface that has the struct class in 
it's signature.

I really want to help you, but I don't think there's any other 
workaround for this issue.

A fix is under review [1], and usually the review takes a couple of 
days, so it should be fixed relatively soon™. But, I can't really say 
anything about Oracle's release schedule for binary bundles.

I know Aleksey Shipilev has recently set up a build-farm as well for 
nightly Linux x86_64 builds: 
https://builds.shipilev.net/openjdk-panama/?C=M&O=D So when the changes 
make it in, you could grab a binary from there as well.

I briefly spoke with some people at AdoptOpenJDK a while ago, and they 
seemed to be interested in doing nightly Panama builds, as long as 
someone could help them set it up. So maybe something can be done 
together with them in the future as well.

Jorn

[1] : 
https://mail.openjdk.java.net/pipermail/panama-dev/2019-February/004378.html

Mark Hammons schreef op 2019-02-16 16:48:
> I'll keep that in mind Jorn, thanks. I found an alternative workaround
> (I found the default function that was being used in place of the
> callback if the callback was null, and just turned that into my
> callback), but now it seems I'm truly blocked by the issue I posted
> about yesterday: Exception in thread "main"
> java.lang.UnsupportedOperationException: bitsSize on Unresolved.
> 
> Using jextract on wlroots introduced a lot of new headers, and a lot
> of cross-header dependencies. There's a struct defined as:
> 
> ```
> 
> @NativeStruct("[${wl_signal}(destroy)${wl_signal}(new_input)${wl_signal}(new_output)](anon$backend_h$444)")
>     public interface anon$backend_h$444 extends
> Struct<backend.anon$backend_h$444> {
>         @NativeLocation(
>             file = "/usr/include/wlr/backend.h",
>             line = 23,
>             column = 20
>         )
>         @NativeGetter("destroy")
>         wl_signal destroy$get();
> 
>         @NativeSetter("destroy")
>         void destroy$set(wl_signal var1);
> 
>         @NativeAddressof("destroy")
>         Pointer<wl_signal> destroy$ptr();
> 
>         @NativeLocation(
>             file = "/usr/include/wlr/backend.h",
>             line = 25,
>             column = 20
>         )
>         @NativeGetter("new_input")
>         wl_signal new_input$get();
> 
>         @NativeSetter("new_input")
>         void new_input$set(wl_signal var1);
> 
>         @NativeAddressof("new_input")
>         Pointer<wl_signal> new_input$ptr();
> 
>         @NativeLocation(
>             file = "/usr/include/wlr/backend.h",
>             line = 27,
>             column = 20
>         )
>         @NativeGetter("new_output")
>         wl_signal new_output$get();
> 
>         @NativeSetter("new_output")
>         void new_output$set(wl_signal var1);
> 
>         @NativeAddressof("new_output")
>         Pointer<wl_signal> new_output$ptr();
>     }
> 
> ```
> 
> and it cannot be instantiated. The ```val l2 =
> Libraries.bind(MethodHandles.lookup(), classOf[wlroots.backend])```
> trick that worked yesterday doesn't work for this either so I'm kinda
> roadblocked.
> 
> Mark
> 
> On 2/16/19 4:31 PM, Jorn Vernee wrote:
>> Hi Mark,
>> 
>> An API for getting a null callback is currently in the process of 
>> being added [1].
>> 
>> In the meantime, there is a way to work around this, but it's tricky 
>> since there doesn't seem to be a public API for parsing a Function 
>> descriptor, or a public API to easily get a layout for a 
>> NativeCallback class (will make a note of that as well). AFAICT it 
>> currently requires manually constructing the Function descriptor for 
>> the callback. But, you should be able to use something like this:
>> 
>> ```
>>     @NativeCallback("()v")
>>     public interface FI1 {
>>         void run();
>>     }
>> 
>>     public static <T> T pointerLiteral(LayoutType<T> type, long value) 
>> {
>>         try(Scope scope = Scope.newNativeScope()) {
>>             Pointer<Long> ptr = scope.allocate(NativeTypes.UINT64);
>>             ptr.set(value);
>>             return ptr.cast(NativeTypes.VOID).cast(type).get();
>>         }
>>     }
>> 
>>     public static void main(String[] args) {
>>         Function f = Function.ofVoid(false, 
>> NativeTypes.VOID.layout());
>>         Address a = Address.ofFunction(64, f);
>>         Callback<FI1> nullCB = pointerLiteral(LayoutType.ofFunction(a, 
>> FI1.class), 0);
>>         System.out.println(nullCB.entryPoint().isNull()); // prints 
>> 'true'
>>     }
>> ```
>> 
>> Hope that helps,
>> Jorn
>> 
>> [1] : 
>> https://mail.openjdk.java.net/pipermail/panama-dev/2019-February/004373.html
>> 
>> Mark Hammons schreef op 2019-02-16 15:53:
>>> Hi,
>>> 
>>> I'm back with a new wayland problem. More specifically, my problem is
>>> with a helper library called wlroots. One of its functions,
>>> wlr_backend_autocreate takes a function pointer as an argument. The
>>> big problem here is that jextract represents this as a Callback<Fi1>,
>>> and part of the valid input for this parameter is the null pointer. 
>>> So
>>> the question is, how do I create a null callback? Can it even be done
>>> with foreign as it's currently made?
>>> 
>>> Thanks,
>>> 
>>> Mark Hammons