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<div class="moz-cite-prefix">On 12/08/2022 16:58, Pedro Lamarão
wrote:<br>
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<div dir="ltr">Em sex., 12 de ago. de 2022 às 12:05, Pedro
Lamarão <<a href="mailto:pedro.lamarao@prodist.com.br" moz-do-not-send="true" class="moz-txt-link-freetext">pedro.lamarao@prodist.com.br</a>>
escreveu:<br>
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<div dir="ltr" class="gmail_attr">Em sex., 12 de ago. de
2022 às 12:01, 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>>
escreveu:<br>
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<p>As I said, I believe this should be visible in
JNI too - but perhaps nobody would write code like
this using JNI. E.g. with JNI, since it's painful
enough to write one native method, developers tend
to "lump" multiple functionalities, e.g. error
checking, in the same native method
implementation. Which, coincidentally, bypasses
some issues that might be visible when using
debuggers (so it is possible that this is a
problem that debuggers never had to worry too much
about).</p>
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<div>Something like this would happen in JNA and JNR
based code.</div>
<div>I am familiar with these; I'll port the original
poster program and push to Github.</div>
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<div>Here: <a href="https://urldefense.com/v3/__https://github.com/pedrolamarao/jvm-getlasterror__;!!ACWV5N9M2RV99hQ!PrCl-0peM-3VuLVa9b6nGGFTnO--4ZJkBXn_fCSvUCnwrceSTXMrlGc8ncp7mCmVpx8rJjH6XIEYny3qeeOPZ1RnFW51VJC7epE$" moz-do-not-send="true">https://github.com/pedrolamarao/jvm-getlasterror</a></div>
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<div>Intellij should be able to understand this with a JDK 19
EA build.</div>
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<div>Simply running the program in the IDE gives the expected
result for "panama" and "jna", but not "jnr", in my machine.</div>
<div>Very interesting.</div>
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<p>Interesting results :-)</p>
<p>In general, there's no silver bullet here. Some frameworks (JNA,
and even JNR - although that didn't seem to work for you) save
certain special values after a given native call (e.g. they save
them in some external thread-local storage).</p>
<p>This of course works because any other components (JVM, debugger,
whatever) can override the value, but will not touch the saved
copy.</p>
<p>That said, the JNA strategy seems more of a workaround to me
(perhaps one that is unavoidable).</p>
<p>For instance, let's say that your application does:</p>
<p>1) a JNA call to some Windows API<br>
2) followed by a JNI call, which makes a bunch of Windows API
calls</p>
<p>Then you ask JNA what's the "last error" and JNA will give you
the error after (1), IIUC.</p>
<p>If this is a problem with the debugger accidentally overwriting
LastError on some platforms, I think it would be perhaps better to
fix it at that level (given that our JVM has some code to defend
against similar accidental overwrites, I'm assuming that it is
possible for the JVM code/debugger code to act in a "transparent"
fashion).</p>
<p>Maurizio<br>
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-- <br>
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<div>Pedro Lamarão</div>
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