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<div class="moz-cite-prefix">On 28/05/2023 20:50, Clayton Walker
wrote:<br>
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<blockquote type="cite" cite="mid:CAEwKcDK-CbRUSjixyg=+9JF4i-8nHhq80YdonYZ2-ggcyKRP_Q@mail.gmail.com">
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<div>I've had success calling jni and awt functions via panama
and jextract-generated bindings. A few notes and questions
below.<br>
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<div><br>
</div>
<div>First off I noticed a bug in jextract, it appears that in
an anonymous union the location will be dumped into the name
field, which is invalid on windows. The backslashes need to be
escaped.</div>
<div>.withName("union (anonymous at
C:\Users\Clayton\.jdks\openjdk-20.0.1\include\win32\jawt_md.h:42:5)"),</div>
<div>I came across this when generating bindings to jawt on
windows. Not sure if it makes sense to include that path or
not but I was able to get around it by adding a Utils.quote
call to Constants.java#340, like so append(".withName(\"" +
Utils.quote(<a href="https://urldefense.com/v3/__http://l.name__;!!ACWV5N9M2RV99hQ!NZzKVdwoqGo5oDo6E4dLPZ7wZ5GFmFyiaSyGJk4cnIuOIOLfZ5PJL3wOxRylvOSOK-dvRUbJ2aHvsD1hLpnVPww8NZZmWkOH4w$" moz-do-not-send="true">l.name</a>().get()) + "\")");</div>
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That seems indeeed a bug - thanks<br>
<blockquote type="cite" cite="mid:CAEwKcDK-CbRUSjixyg=+9JF4i-8nHhq80YdonYZ2-ggcyKRP_Q@mail.gmail.com">
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<div><br>
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<div>Secondly, when using jextract does it make sense to call
jextract once? For example, there are jni functions that come
from jni.dll, but there are also awt functions that come from
jawt.dll. Some of these functions share definitions. Certain
functions need jni loaded, and certain ones need jawt. It
doesn't necessarily make sense to load jawt if only jni
functions are going to be called, but in my case it's fine. Is
it expected for developers to call jextract twice, once per
library, or to perhaps create a meta-header that references
both?</div>
</div>
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<p>I think creating the meta-header which includes both and passing
that to jextract is a fine approach here. Note that you can also
use the options for printing all symbols and then filtering them,
as explained here:</p>
<p><a class="moz-txt-link-freetext" href="https://github.com/openjdk/jextract#filtering-symbols">https://github.com/openjdk/jextract#filtering-symbols</a><br>
</p>
<blockquote type="cite" cite="mid:CAEwKcDK-CbRUSjixyg=+9JF4i-8nHhq80YdonYZ2-ggcyKRP_Q@mail.gmail.com">
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<div><br>
</div>
<div>Also related to the above question, there are
platform-specific headers, jni_md.h and jawt_md.h that differ
depending on the platform. How are developers encouraged to
share code in this place? Generate all platform definitions at
once, or once per platform then merge the definitions, or once
per platform and keep their jextract-extracted source
separate?</div>
</div>
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<p>I think the last option you mention is the most frequent I've
seen used. Jextract itself does something different when
interacting with libclang, as libclang is written in portable C
(so e.g. uses "long long" instead of "long") and all layouts ends
up being ok across platforms, so that we don't really need
different versions. My feeling is that jni itself should be
portable (after all, JNI types are modelled after _Java_ types,
whose sizes are known), I don't know about jawt. But it is
possible that the differences are related to functions you don't
care about? (in which case, extracting a mininum common
denominator wouldn't be too bad?)</p>
<p>Maurizio<br>
</p>
<blockquote type="cite" cite="mid:CAEwKcDK-CbRUSjixyg=+9JF4i-8nHhq80YdonYZ2-ggcyKRP_Q@mail.gmail.com">
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<div dir="ltr" class="gmail_attr">On Wed, May 24, 2023 at
3:08 PM Maurizio Cimadamore <<a href="mailto:maurizio.cimadamore@oracle.com" moz-do-not-send="true" class="moz-txt-link-freetext">maurizio.cimadamore@oracle.com</a>>
wrote:<br>
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0.8ex;border-left:1px solid rgb(204,204,204);padding-left:1ex">
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<div>On 24/05/2023 20:36, Clayton Walker wrote:<br>
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<blockquote type="cite">
<div dir="ltr">Hi Maurizio,
<div>thanks for the detailed response!</div>
<div><br>
</div>
<div>I believe I understood this for the most part, but
a quick question related to the jni references. Do we
need to use NewGlobalRef so that we can exit the
native jni function and not have their jni reference
freed?</div>
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Yes, the global ref is required given that we go in and out
of JNI functions. Are you worried about the cost of creating
global references? (Trying to understand more about the use
case)<br>
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<div><br>
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<div>Also would it make more sense to go this route than
to expose a new function called (e.g.)
getDrawingSurface method to the awt Component class
which returns a MemorySegment that we can free?
Presumably to avoid cluttering up awt/swing with
additional native function calls, or perhaps avoid
leaking implementation details to the java standard
library?</div>
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<p>I'm not an expert in AWT/Swing - but it would seem that,
at a glance, the Component class doesn't have much in
terms of low-level capabilities. So exposing a method
which returns a segment (or a ByteBuffer) would look a bit
odd, I think.</p>
<p>Cheers<br>
Maurizio<br>
</p>
<blockquote type="cite"><br>
<div class="gmail_quote">
<div dir="ltr" class="gmail_attr">On Wed, May 24, 2023
at 12:22 PM Maurizio Cimadamore <<a href="mailto:maurizio.cimadamore@oracle.com" target="_blank" moz-do-not-send="true" class="moz-txt-link-freetext">maurizio.cimadamore@oracle.com</a>>
wrote:<br>
</div>
<blockquote class="gmail_quote" style="margin:0px 0px
0px 0.8ex;border-left:1px solid
rgb(204,204,204);padding-left:1ex">
<div>
<p>Hi Clayton<br>
interacting with JNI code has few issues:<br>
<br>
1. you need a JNIEnv* segment<br>
2. you need to be able to wrap Java objects as JNI
references (so that they can be passed as pointers
to native calls)<br>
3. expose some way to map method names into JNI
mangled names (so that we can look those up using
a symbol lookup)<br>
</p>
<p>This is something on our radar and we will like
to address this use case at some point (but it is
possible this might be addressed _after_ the FFM
API is finalized). Two possible approaches are:</p>
<p>* a set of static helper functions which allow to
obtain JNIEnv segment, as well as create,
dereference and destroy JNI refs. We might even
expose JNI functions here (think of a JNIUtils
class)<br>
* a true JNILinker <: Linker - this might allow
a tighter coupling with JNI functions (as the
JNIEnv will be passed automatically)<br>
</p>
<p>I think the former approach is quite attractive
in terms of bang for bucks. It doesn't add a lot
of complexity to the API, and adds the minimum
functionality that is required in order to allow
the native linker to deal with JNI functions as
well (even though developers will need to take
some extra care when doing so).</p>
<p>In the meantime, I think it might be possible to
define a small JNI library which takes care of the
missing functionalities - e.g. it could
return/accept JNI references as "jlong" (an hack,
I know) so, something like this:<br>
</p>
<p>native long makeGlobalRef(Object o) // call
NewGlobalRef, cast result to jlong and return<br>
native void destroyGlobalRef(long ref) // cast to
jobject, then call DeleteGlobalRef<br>
native Object readGlobalRef(long ref) // cast to
jobject, return<br>
native long getEnv(); // cast env parameter to
jlong and return<br>
</p>
<p>I've tried something along those lines and it
seems to work as expected. But I agree that it
would be convenient if this "just worked" out of
the box.</p>
<p>Cheers<br>
Maurizio<br>
</p>
<p><br>
</p>
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<div>On 24/05/2023 18:28, Clayton Walker wrote:<br>
</div>
<blockquote type="cite">
<div dir="ltr">I am working on a project with one
of the goals being able to use a swing component
as a render target. From the documentation <a href="https://docs.oracle.com/javase/8/docs/technotes/guides/awt/AWT_Native_Interface.html" target="_blank" moz-do-not-send="true">here</a> I
assume we need jni in order to access the native
PlatformInfo struct. My question is the same as
asked in <a href="https://urldefense.com/v3/__https://stackoverflow.com/questions/75620948/how-do-i-get-the-hwnd-of-a-canvas-using-panama__;!!ACWV5N9M2RV99hQ!Pq0tFxFIxoDHgX_vezwj24Kuk4wsYvPXLMS09T7SYv_UyIpO7nN_Sc1jmNWMzwSORL6P3_hbxJIXfK4h2FNcd_LAkn4CRaOc8w$" target="_blank" moz-do-not-send="true">this
stackoverflow question</a>, is it possible to
use panama to get the HWND of a swing window?</div>
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