<div dir="ltr">Those 3 alternatives make sense from my POV and look complementary:<br> - JCMD could be used by sysops and for testing.<br> - API could potentially be used by a Spring Boot actuator [1] exposing a secured endpoint allowing to trigger the end of a training run.<br> - Commandline could be useful for platforms wanting to provide AOT cache support with the knowledge of the frameworks used. For example, it could be used to specify `-XX:CDSEndTrainingOnEntry=org.springframework.web.servlet.DispatcherServlet#doService` after 10000 invocations.<br><br>If that's a new capability, would it make sense to only expose it via `-XX:AOTEndTrainingOnEntry` instead of `-XX:CDSEndTrainingOnEntry` to avoid too many options and some confusion?<br><br>Providing those capabilities will be very important when AOT profiles and AOT compiled methods will be available as they could allow target use cases where the production environment is used to get profiling data (will be the most popular use case IMO), and you would typically want to dump the profiling data without killing the instance. That said, it could maybe ease integrators' work to support those capabilities earlier than AOT profiles and AOT compiled methods, if that makes sense with the current feature set. For example, it could allow platforms and frameworks to be "Leyden-ready" with a Java 25 minimal requirement if we consider those JCMD/API/Commandline as a subset of "Leyden public API". AOT profiles and AOT compiled methods support could come later and be almost an implementation detail from platforms and frameworks POV.<br><br>Since the creation of an AOT cache with Spring Petclinic was pretty long and resource consuming last time I tried, I am wondering if it could be possible to provide an option to control what kind of output we expect at the end of the training run. Generating directly the CDS/AOT archive makes sense, but on production it could be potentially too resource consuming and would produce too many side effects. Like the JEP 483 differentiates the AOT configuration recorded (app.aotconf) from the cache (app.aot), would it be possible with AOT profiles and AOT compiled methods to optionally generate an intermediate format that would be fast to generate at the end of the training, and defer the more involved creation of the archive at a later point (keeping the constraints of same OS, Java version and classpath)?<br></div><br><div class="gmail_quote gmail_quote_container"><div dir="ltr" class="gmail_attr">On Thu, Mar 6, 2025 at 9:23 PM <<a href="mailto:ioi.lam@oracle.com">ioi.lam@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"><u></u>
<div>
<p>With JEP 483 [1], the profiling data (AOT config file) are
captured when the training run exits. In the Leyden repo, we have
implemented a mechanism [2] to capture the profiler data at an
earlier point. Excerpt from [2]:</p>
<p><br>
</p>
<p>===</p>
<p><span style="color:rgb(23,43,77);font-family:"DejaVu Sans",sans-serif;font-size:14px;font-style:normal;font-variant-ligatures:normal;font-variant-caps:normal;font-weight:400;letter-spacing:normal;text-align:left;text-indent:0px;text-transform:none;word-spacing:0px;white-space:normal;background-color:rgb(255,255,255);text-decoration-style:initial;text-decoration-color:initial;float:none;display:inline">It
may be difficult for users to run to normal completion for all
training runs - some may prefer to only record data until the
application framework has started or prior to some method being
invoked.</span><br style="color:rgb(23,43,77);font-family:"DejaVu Sans",sans-serif;font-size:14px;font-style:normal;font-variant-ligatures:normal;font-variant-caps:normal;font-weight:400;letter-spacing:normal;text-align:left;text-indent:0px;text-transform:none;word-spacing:0px;white-space:normal;background-color:rgb(255,255,255);text-decoration-style:initial;text-decoration-color:initial">
<br style="color:rgb(23,43,77);font-family:"DejaVu Sans",sans-serif;font-size:14px;font-style:normal;font-variant-ligatures:normal;font-variant-caps:normal;font-weight:400;letter-spacing:normal;text-align:left;text-indent:0px;text-transform:none;word-spacing:0px;white-space:normal;background-color:rgb(255,255,255);text-decoration-style:initial;text-decoration-color:initial">
<span style="color:rgb(23,43,77);font-family:"DejaVu Sans",sans-serif;font-size:14px;font-style:normal;font-variant-ligatures:normal;font-variant-caps:normal;font-weight:400;letter-spacing:normal;text-align:left;text-indent:0px;text-transform:none;word-spacing:0px;white-space:normal;background-color:rgb(255,255,255);text-decoration-style:initial;text-decoration-color:initial;float:none;display:inline">This
RFE is to track other possible triggers for CDS data to be
collected and / or for the _assembly phase_ to being.</span><br style="color:rgb(23,43,77);font-family:"DejaVu Sans",sans-serif;font-size:14px;font-style:normal;font-variant-ligatures:normal;font-variant-caps:normal;font-weight:400;letter-spacing:normal;text-align:left;text-indent:0px;text-transform:none;word-spacing:0px;white-space:normal;background-color:rgb(255,255,255);text-decoration-style:initial;text-decoration-color:initial">
<br style="color:rgb(23,43,77);font-family:"DejaVu Sans",sans-serif;font-size:14px;font-style:normal;font-variant-ligatures:normal;font-variant-caps:normal;font-weight:400;letter-spacing:normal;text-align:left;text-indent:0px;text-transform:none;word-spacing:0px;white-space:normal;background-color:rgb(255,255,255);text-decoration-style:initial;text-decoration-color:initial">
<span style="color:rgb(23,43,77);font-family:"DejaVu Sans",sans-serif;font-size:14px;font-style:normal;font-variant-ligatures:normal;font-variant-caps:normal;font-weight:400;letter-spacing:normal;text-align:left;text-indent:0px;text-transform:none;word-spacing:0px;white-space:normal;background-color:rgb(255,255,255);text-decoration-style:initial;text-decoration-color:initial;float:none;display:inline">(a)
JCMD: a new jcmd can be developed to attach to a running JVM and
signal the training run has ended. For classic CDS, this may be
the point at which the classlist is dumped to the file. For
premain CDS, this may trigger the start of the assembly phase
and the creation of the CDS archive.</span><br style="color:rgb(23,43,77);font-family:"DejaVu Sans",sans-serif;font-size:14px;font-style:normal;font-variant-ligatures:normal;font-variant-caps:normal;font-weight:400;letter-spacing:normal;text-align:left;text-indent:0px;text-transform:none;word-spacing:0px;white-space:normal;background-color:rgb(255,255,255);text-decoration-style:initial;text-decoration-color:initial">
<br style="color:rgb(23,43,77);font-family:"DejaVu Sans",sans-serif;font-size:14px;font-style:normal;font-variant-ligatures:normal;font-variant-caps:normal;font-weight:400;letter-spacing:normal;text-align:left;text-indent:0px;text-transform:none;word-spacing:0px;white-space:normal;background-color:rgb(255,255,255);text-decoration-style:initial;text-decoration-color:initial">
<span style="color:rgb(23,43,77);font-family:"DejaVu Sans",sans-serif;font-size:14px;font-style:normal;font-variant-ligatures:normal;font-variant-caps:normal;font-weight:400;letter-spacing:normal;text-align:left;text-indent:0px;text-transform:none;word-spacing:0px;white-space:normal;background-color:rgb(255,255,255);text-decoration-style:initial;text-decoration-color:initial;float:none;display:inline">(b)
API: a new Leyden-specific API may be created that allows
developers to indicate programatically the point at which the
training run should end. This could be as simple as a static
method `Leyden.endTraining()` or something that exposes more
state such as the name of the CDS file. Details TBD based on
need.</span><br style="color:rgb(23,43,77);font-family:"DejaVu Sans",sans-serif;font-size:14px;font-style:normal;font-variant-ligatures:normal;font-variant-caps:normal;font-weight:400;letter-spacing:normal;text-align:left;text-indent:0px;text-transform:none;word-spacing:0px;white-space:normal;background-color:rgb(255,255,255);text-decoration-style:initial;text-decoration-color:initial">
<br style="color:rgb(23,43,77);font-family:"DejaVu Sans",sans-serif;font-size:14px;font-style:normal;font-variant-ligatures:normal;font-variant-caps:normal;font-weight:400;letter-spacing:normal;text-align:left;text-indent:0px;text-transform:none;word-spacing:0px;white-space:normal;background-color:rgb(255,255,255);text-decoration-style:initial;text-decoration-color:initial">
<span style="color:rgb(23,43,77);font-family:"DejaVu Sans",sans-serif;font-size:14px;font-style:normal;font-variant-ligatures:normal;font-variant-caps:normal;font-weight:400;letter-spacing:normal;text-align:left;text-indent:0px;text-transform:none;word-spacing:0px;white-space:normal;background-color:rgb(255,255,255);text-decoration-style:initial;text-decoration-color:initial;float:none;display:inline">(c)
Commandline: a new option could specify when to trigger the end
of the training run. ie:
`-XX:CDSEndTrainingOnEntry=org.foo.bar.someMethod`. This can be
extended beyond single entry to also include a counted entry ie:
the 1000 time this method is entered.</span></p>
<p><span style="color:rgb(23,43,77);font-family:"DejaVu Sans",sans-serif;font-size:14px;font-style:normal;font-variant-ligatures:normal;font-variant-caps:normal;font-weight:400;letter-spacing:normal;text-align:left;text-indent:0px;text-transform:none;word-spacing:0px;white-space:normal;background-color:rgb(255,255,255);text-decoration-style:initial;text-decoration-color:initial;float:none;display:inline">===<br>
</span></p>
<p><span style="color:rgb(23,43,77);font-family:"DejaVu Sans",sans-serif;font-size:14px;font-style:normal;font-variant-ligatures:normal;font-variant-caps:normal;font-weight:400;letter-spacing:normal;text-align:left;text-indent:0px;text-transform:none;word-spacing:0px;white-space:normal;background-color:rgb(255,255,255);text-decoration-style:initial;text-decoration-color:initial;float:none;display:inline"><br>
</span></p>
<p>As of today, (a) and (c) have been implemented in the Leyden
repo. We have received positive feedback from developers who found
this mechanism to be useful and are requesting for similar
features in the JDK mainline.</p>
<p>I think now will be a good time to have a wider discussion with
the community about:</p>
<p>- The use case and requirements for such a mechanism</p>
<p>- The solution space -- besides the 3 options listed above, are
there other approaches? Pros & cons?</p>
<p>For example, an API might be more precise. However, many apps are
built with 3rd libraries that cannot be modified easily, so an
external mechanism would be preferable. JCMD might be least
intrusive, but it's timing dependent and may not be available (in
containers, etc).<br>
</p>
<p><br>
</p>
<p>--------------------------------------<br>
</p>
<p>[1] <a href="https://openjdk.org/jeps/483" target="_blank">https://openjdk.org/jeps/483</a><br>
</p>
<p>[2] <a href="https://bugs.openjdk.org/browse/JDK-8335358" target="_blank">https://bugs.openjdk.org/browse/JDK-8335358</a><br>
</p>
</div>
</blockquote></div>
<br>
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