Re: Re[2]: How to do “--add-modules” with dynamically created layer in JPMS?

[Christian Stein]

Hi Alex,

Perhaps a deeper look how Layrry works under the hood does help:
https://github.com/moditect/layrry
If I'm not mistaken, your use-case seems very similar to those Layrry tries
to cope with.

Cheers,
Christian


On Mon, Nov 16, 2020 at 10:17 AM Alex Orlov <ooo_saturn7 at mail.ru> wrote:

>
> Hello Alan,
>
> Thank you for such detailed answer. I read it with attention, but still
> don’t know how to solve my situation.
> Maybe may question didn’t provide all details, so here they are.
>
> I want to create the following layer structure:
>
> +++++++++++
> + Boot Layer +
> +++++++++++
>        |
>        +++++++++++++++++
>        + Web Server Layer +
>        +++++++++++++++++
>                          |
>                          ++++++++++++++++++++
>                          + Web Application Layer +
>                          ++++++++++++++++++++
>
> So, we have always one boot layer (it’s clear), one web server layer, and
> multiple web application layers. At
> the same time all web application layers have one parent — web server
> layer. Boot layer doesn’t know and mustn’t know
> about any child layer modules!!!! So it is impossible to add all modules
> to boot layer!
>
> In web server layer I have servlet container (Jetty) and rest
> implementation (Jersey). When I create web server layer
>
> Configuration cf =
> parentLayer.configuration().resolveAndBind(moduleFinder, ModuleFinder.of(),
> moduleNames);
> ModuleLayer layer = parentLayer.defineModulesWithOneLoader(cf,
> parentClassLoader);
>
> I add to it all modules of jetty, jersey and their dependencies. At the
> same time jetty knows nothing about jersey. When web server layer is
> created one of its modules starts Jetty.
>
> So, when does jersey start? It starts only when web application layer is
> created with .war file that has web.xml with jersey servlet. For example:
>
> <servlet>
>         <servlet-name>JerseyServlet</servlet-name>
>
> <servlet-class>org.glassfish.jersey.servlet.ServletContainer</servlet-class>
> </servlet>
>
> So, in such configuration, when web server layer is created no one can
> know if jersey will be used.
>
> What what does JPMS do? It ignores all jersey modules including all its
> dependencies (including API). So, the question.
> How to ask JPMS not to ignore modules that it must add to layer?
>
>
>
>
>
> --
> Best regards, Alex Orlov
>
>
> >Понедельник, 16 ноября 2020, 11:20 +03:00 от Alan Bateman <
> alan.bateman at oracle.com>:
> >
> >On 15/11/2020 19:16, Alex Orlov wrote:
> >> Hi all,
> >>
> >> I create JPMS layer this way:
> >>
> >> Configuration cf =
> parentLayer.configuration().resolveAndBind(moduleFinder, ModuleFinder.of(),
> moduleNames);
> >> ModuleLayer layer = parentLayer.defineModulesWithOneLoader(cf,
> parentClassLoader);
> >>
> >> And I have a problem with adding implementation modules. These
> implementation modules are ignored by JPMS because classes from these
> modules are not used anywhere (it is clear, that classes from API modules
> are used). So, JPMS doesn't add these modules to layer.
> >>
> >> As I understand, if I spoke about implementation modules on boot layer,
> I could use --add-modules jvm argument. However, I couldn't find any
> information how to force JPMS load my module (even if its classes are not
> used) for dynamically created layers.
> >>
> >> Could anyone say how to do it? It would be useful if you could give an
> example of "implementation
> >module". I can't tell if you mean a jdk.* module, a service provider
> >module that doesn't export an API, or something else.
> >
> >In any case, I think the picture you are describing is a module that is
> >observable, either in the run-time image or on module path. The module
> >is not resolved at startup (and so is not in the boot layer) because the
> >initial module that you specify with `java -m` doesn't transitively
> >require it and it doesn't provide an implementation of a service that
> >any of the other resolved modules use.
> >
> >The summary is a module layer is immutable and there isn't any way to
> >add modules to a module layer once it has been created. For what you are
> >doing then maybe `--add-modules ALL-SYSTEM` can be used as workaround.
> >This will ensure that all system/platform modules are in the boot layer
> >as these modules cannot be loaded into a child layer (Johannes's suggest
> >to specify the module name to resolveAndBind will not work for java.*
> >modules as they cannot be loaded into child layers, his suggestion may
> >work for other modules).
> >
> >One other point to mention is that the original set of requirement
> >envisaged some means to augment the set of platform modules at run-time.
> >We didn't get to that requirement except for the limited scenario that
> >is tools loading the JMX agent or a java agent into a running VM. These
> >limited scenario involve loading the jdk.management.agent or
> >java.instrument modules and that is some with a special child layer
> >rather than augmenting the boot layer. This partial solution, along with
> >`--add-modules ALL-SYSTEM`as a workaround for the general cases, has
> >been sufficient to date.
> >
> >-Alan
>