[forge-dev] shading!?

Lincoln Baxter, III lincolnbaxter at gmail.com
Wed Apr 20 12:34:42 EDT 2011


I think what JBoss Modules can give you is a functional, safe
> multiple-delegate class loader which you can't get with URL class loaders.
>  Specifically, f you want to have a _graph_ of class loaders (as opposed to
> individual flat, merged classloaders) then you need something like Modules.
>

I think I just embarrassed myself ;) But can weld even handle this kind of
separate class-loader situation?


> As far as Maven integration, you could write a ModuleLoader which does this
> for you.  You'd have to do version management on your own though. Perhaps
> you could use Aether for the purpose of resolving and fetching artifacts,
> and then use information exposed therefrom to construct the module graph.
>

Right, which is something Forge can already do pretty handily (using
Aether):
https://github.com/seam/forge/blob/master/shell-api/src/main/java/org/jboss/seam/forge/project/dependencies/DependencyResolverProvider.java


> http://www.sonatype.com/people/2010/08/introducing-aether/
>
> Your application does not have to be modular to use JBoss Modules. Though
> of course in my opinion that makes it much nicer. :-)
>
>
> On 04/20/2011 10:56 AM, Lincoln Baxter, III wrote:
>
>> I agree with both of you guys, which is why I am soliciting ideas for
>> this now.
>>
>> I can also say that we do not have one big Classpath right now (unless I
>> am horribly mistaken.) Forge already supports classpath isolation of
>> individual plugins, so we're already half-way there. If my understanding
>> of classloaders is at all right, It would not be too much work to
>> implement a maven resolver and additional level of Composite
>> classloaders to achieve this goal.
>>
>> I don't believe we need to pull in a heavyweight module system like
>> OSGI, or force developers to do even the simple configuration for
>> something like JBoss modules (which afaik, does not have a way of
>> packaging the actual dependencies with the module, or calling out to
>> Maven for dependencies - which forge can already do.)
>>
>> *This is what we have right now:* (see today.png)
>>
>> Notice how the Plugin ClassLoaders may reference Forge APIs, but the
>> plugins may not access each other's classloaders because there is no
>> link from Forge APIs to the Plugins.
>>
>> *And this is all I think it should take to do what I am suggesting:*
>> (see tomorrow.png)
>>
>> If it is technically possible to achieve with JBoss modules, via adding
>> in parsing the POM and including dependencies automatically, then I am
>> all for it, but from what I understand, this would not really be a 1-1
>> mapping and will not be trivial. I know my understanding of ClassLoaders
>> may be a bit Naive, but I don't think that we need to use JBoss modules
>> (or OSGi) to achieve this goal of automatic downloading and loading of
>> plugin dependency JARs.
>>
>> We certainly do not need the ability (yet) to drop an individual module
>> while Forge is running, because Weld does not support this kind of
>> disruption in the BeanStore. If you remove a JAR while Weld is running,
>> you get a big fiery explosion. Same for loading a single JAR, you have
>> to restart Weld because it will not be aware of the changes, and there
>> is not a good API to make it so. It still has to build the bean graph
>> all over again. That is one of the big reasons to use a fully-fledged
>> module system, and we don't have that requirement. Forge simply dumps
>> all classloaders (until JDK 7 we can't close them easily, yeah memory
>> leaks, whatever, not really important right now,) then builds a new
>> network of ClassLoaders and starts over.
>>
>> However, if we can extend JBoss modules with Maven support in this way,
>> and it's something that David would be interested in, then I think
>> that's one big reason to do it that way. Until then, if we can do it
>> quickly my way, I'd like to get it working sooner rather than later.
>> Please please tell me (I'm sure I don't even have to ask) if there are
>> gaping technical holes in what I am proposing, but if there are not,
>> then I'm going to stick to this position until someone bursts my bubble.
>>
>> ~Lincoln
>>
>>
>> On Wed, Apr 20, 2011 at 9:33 AM, Paul Bakker <paul.bakker.nl
>> <http://paul.bakker.nl>@gmail.com <http://gmail.com>> wrote:
>>
>>    Yeah, I'm afraid that's right. I think the module system integration
>>    should get very high priority before we reach a 1.0 version. It's
>>    something that affects the whole way the core is built up, and it
>>    will be very difficult to change that later on.
>>
>>    Paul
>>
>>
>>
>>
>>    On Wed, Apr 20, 2011 at 3:17 PM, Max Rydahl Andersen
>>    <max.andersen at redhat.com <mailto:max.andersen at redhat.com>> wrote:
>>
>>        +1
>>
>>        I agree with what you want to do Lincoln, but don't see how that
>>        can be made to happen without a module system.
>>
>>        Until then everything just will have to live in one big classpath.
>>
>>        /max
>>
>>        On Apr 20, 2011, at 14:24, Paul Bakker wrote:
>>
>>         > And that's why a module system is needed. If people can just
>>        add dependencies there will be duplicate (possibly multiple
>>        versions) dependencies. Each plugin should be in a separate
>>        classloader, and each dependency should be too so that a plugin
>>        never breaks other plugins or Forge itself. It would be a big
>>        limitation if plugins can't use libraries otherwise.
>>         >
>>         > Paul
>>         >
>>         > On Tue, Apr 19, 2011 at 6:14 PM, Lincoln Baxter, III
>>        <lincolnbaxter at gmail.com <mailto:lincolnbaxter at gmail.com>> wrote:
>>         > That's right, but what I'm saying is that I don't want
>>        developers to be responsible for anything but *their code* -- if
>>        they have dependencies, those depenencies will be fetched for
>>        them (or somehow bundled in the JAR file itself, which is
>>        certainly possible, however not my preference.)
>>         >
>>         > If you could write a plugin, reference dependencies in your
>>        POM, and have everything *Just Work* don't you think that would
>>        be a friendlier experience?
>>         >
>>         > ~Lincoln
>>         >
>>         >
>>         > On Mon, Apr 18, 2011 at 5:55 PM, Max Andersen
>>        <manderse at redhat.com <mailto:manderse at redhat.com>> wrote:
>>         > But if your plugin uses multiple jars it is not one jar.
>>         >
>>         >
>>         > /max (sent from my phone)
>>         >
>>         >
>>         > On 18/04/2011, at 19.06, "Lincoln Baxter, III"
>>        <lincolnbaxter at gmail.com <mailto:lincolnbaxter at gmail.com>> wrote:
>>         >
>>         >> That doesn't solve the problem of having to drop jar files
>>        onto the classpath in order for plugins to work. I want one JAR
>>        per plugin.
>>         >>
>>         >> ~Lincoln
>>         >>
>>         >> On Mon, Apr 18, 2011 at 12:59 PM, Max Rydahl Andersen
>>        <max.andersen at redhat.com <mailto:max.andersen at redhat.com>> wrote:
>>         >>
>>         >> On Apr 18, 2011, at 18:57, Lincoln Baxter, III wrote:
>>         >>
>>         >> > I don't want to force plugin-developers to create modules
>>        for every dependency that their plugin requires. That's why I've
>>        been avoiding OSGI or JBoss Modules.
>>         >>
>>         >> But then you shouldn't be forcing them to shade either - you
>>        should just have one global classloader for the plugins then.
>>         >>
>>         >> /max
>>         >>
>>         >> >
>>         >> > ~Lincoln
>>         >> >
>>         >> > On Mon, Apr 18, 2011 at 12:37 PM, Max Rydahl Andersen
>>        <max.andersen at redhat.com <mailto:max.andersen at redhat.com>> wrote:
>>         >> >
>>         >> > > What do you think about using Maven APIs to inspect the
>>        POM and fetch dependencies dynamically for each plugin, then
>>        isolate them in the plugin's classloader?
>>         >> >
>>         >> > Why not just load them in to one classloader so you don't
>>        have collisions when there are mixed dependencies on Forge it self
>> ?
>>         >> >
>>         >> > How about shared data instances ? How does that work ?
>>         >> >
>>         >> > ...as a side note...creating our own module system now - I
>>        feel that is a very bad direction :(
>>         >> > Might as well adopt osgi plugin system if you want this
>>        kind of separation ?
>>         >> >
>>         >> > /max
>>         >> >
>>         >> > >
>>         >> > > ~Lincoln
>>         >> > >
>>         >> > > On Mon, Apr 18, 2011 at 11:56 AM, Max Rydahl Andersen
>>        <max.andersen at redhat.com <mailto:max.andersen at redhat.com>> wrote:
>>         >> > >
>>         >> > > On Apr 18, 2011, at 15:15, Lincoln Baxter, III wrote:
>>         >> > >
>>         >> > > > "if there is a standard location for dependencies"
>>         >> > > >
>>         >> > > > What do you mean?
>>         >> > >
>>         >> > > Your "standard" for shading is that you put all classes
>>        into the plugin.jar.
>>         >> > >
>>         >> > > A "standard" for dependencies for a plugin.jar could be
>>        "next to the plugin.jar".
>>         >> > >
>>         >> > > Would still have the problem of overlapping jars but
>>        then at least its easier to see where the duplication is.
>>         >> > >
>>         >> > > /max
>>         >> > >
>>         >> > > >
>>         >> > > > Thx,
>>         >> > > > ~Lincoln
>>         >> > > >
>>         >> > > > On Mon, Apr 18, 2011 at 6:20 AM, Max Rydahl Andersen
>>        <max.andersen at redhat.com <mailto:max.andersen at redhat.com>> wrote:
>>         >> > > >
>>         >> > > > > I was thinking we might already be able to do that
>>        using the existing pom.xml metadata that's stored in the
>>        artifact itself, or is that too tricky?
>>         >> > > >
>>         >> > > > if there is a standard location for dependencies then
>>        it should be fine - at least better than shading ;)
>>         >> > > >
>>         >> > > > /max
>>         >> > > >
>>         >> > > > >
>>         >> > > > > On Mon, Apr 11, 2011 at 6:51 PM, Max Andersen
>>        <manderse at redhat.com <mailto:manderse at redhat.com>> wrote:
>>         >> > > > > I was thinking Plugin jar having references to
>>        dependent jars via manifest.mf
>>         >> > > > >
>>         >> > > > > /max (sent from my phone)
>>         >> > > > >
>>         >> > > > >
>>         >> > > > > On 12/04/2011, at 00.39, "Lincoln Baxter, III"
>>        <lincolnbaxter at gmail.com <mailto:lincolnbaxter at gmail.com>> wrote:
>>         >> > > > >
>>         >> > > > >> Can you give an example of how you would bundle the
>>        JARs? (Just put them in /META-INF/dependencies/ ... ?) And would
>>        that not cause just as many class conflicts? If you
>>        shade/relocate then the deps *should be* completely isolated.
>>         >> > > > >>
>>         >> > > > >> On Mon, Apr 11, 2011 at 4:11 PM, Max Rydahl
>>        Andersen <max.andersen at redhat.com
>>        <mailto:max.andersen at redhat.com>> wrote:
>>         >> > > > >> well, recommending just bundling jars would be a
>>        better approach than shading IMO.
>>         >> > > > >>
>>         >> > > > >> /max
>>         >> > > > >>
>>         >> > > > >> On Apr 11, 2011, at 16:00, Lincoln Baxter, III wrote:
>>         >> > > > >>
>>         >> > > > >> > Yeah, shading is currently the recommended
>>        approach. Conflicts should be avoided by using relocations. I
>>        know this is... not a great method, but for now it's all we've
>>        got. Open to suggestions.
>>         >> > > > >> >
>>         >> > > > >> > ~Lincoln
>>         >> > > > >> >
>>         >> > > > >> > On Mon, Apr 11, 2011 at 3:41 AM, Max Rydahl
>>        Andersen <max.andersen at redhat.com
>>        <mailto:max.andersen at redhat.com>> wrote:
>>         >> > > > >> > Heya,
>>         >> > > > >> >
>>         >> > > > >> > Lincoln, I just saw your commits to hibernattools
>>        plugin at
>>        (
>> https://github.com/forge/plugin-hibernate-tools/commit/8b208b4a8e79dbb8a01d10d266ee81afd2cf7106
>> )
>>         >> > > > >> >
>>         >> > > > >> > Is shading of jars really the recommended
>>        approach for plugins in Forge ?
>>         >> > > > >> >
>>         >> > > > >> > How are you going to share/avoid collisions of
>>        libraries across plugins if they need to bundle via shading ?
>>         >> > > > >> >
>>         >> > > > >> > /max
>>         >> > > > >> > http://about.me/maxandersen
>>         >> > > > >> >
>>         >> > > > >> >
>>         >> > > > >> >
>>         >> > > > >> >
>>         >> > > > >> > _______________________________________________
>>         >> > > > >> > forge-dev mailing list
>>         >> > > > >> > forge-dev at lists.jboss.org
>>        <mailto:forge-dev at lists.jboss.org>
>>
>>         >> > > > >> > https://lists.jboss.org/mailman/listinfo/forge-dev
>>         >> > > > >> >
>>         >> > > > >> >
>>         >> > > > >> >
>>         >> > > > >> > --
>>         >> > > > >> > Lincoln Baxter, III
>>         >> > > > >> > http://ocpsoft.com
>>         >> > > > >> > http://scrumshark.com
>>         >> > > > >> > "Keep it Simple"
>>         >> > > > >>
>>         >> > > > >> /max
>>         >> > > > >> http://about.me/maxandersen
>>         >> > > > >>
>>         >> > > > >>
>>         >> > > > >>
>>         >> > > > >>
>>         >> > > > >>
>>         >> > > > >>
>>         >> > > > >> --
>>         >> > > > >> Lincoln Baxter, III
>>         >> > > > >> http://ocpsoft.com
>>         >> > > > >> http://scrumshark.com
>>         >> > > > >> "Keep it Simple"
>>         >> > > > >
>>         >> > > > >
>>         >> > > > >
>>         >> > > > > --
>>         >> > > > > Lincoln Baxter, III
>>         >> > > > > http://ocpsoft.com
>>         >> > > > > http://scrumshark.com
>>         >> > > > > "Keep it Simple"
>>         >> > > >
>>         >> > > > /max
>>         >> > > > http://about.me/maxandersen
>>         >> > > >
>>         >> > > >
>>         >> > > >
>>         >> > > >
>>         >> > > >
>>         >> > > >
>>         >> > > > --
>>         >> > > > Lincoln Baxter, III
>>         >> > > > http://ocpsoft.com
>>         >> > > > http://scrumshark.com
>>         >> > > > "Keep it Simple"
>>         >> > >
>>         >> > > /max
>>         >> > > http://about.me/maxandersen
>>         >> > >
>>         >> > >
>>         >> > >
>>         >> > >
>>         >> > >
>>         >> > >
>>         >> > > --
>>         >> > > Lincoln Baxter, III
>>         >> > > http://ocpsoft.com
>>         >> > > http://scrumshark.com
>>         >> > > "Keep it Simple"
>>         >> >
>>         >> > /max
>>         >> > http://about.me/maxandersen
>>         >> >
>>         >> >
>>         >> >
>>         >> >
>>         >> >
>>         >> >
>>         >> > --
>>         >> > Lincoln Baxter, III
>>         >> > http://ocpsoft.com
>>         >> > http://scrumshark.com
>>         >> > "Keep it Simple"
>>         >>
>>         >> /max
>>         >> http://about.me/maxandersen
>>         >>
>>         >>
>>         >>
>>         >>
>>         >>
>>         >>
>>         >> --
>>         >> Lincoln Baxter, III
>>         >> http://ocpsoft.com
>>         >> http://scrumshark.com
>>         >> "Keep it Simple"
>>         >
>>         >
>>         >
>>         > --
>>         > Lincoln Baxter, III
>>         > http://ocpsoft.com
>>         > http://scrumshark.com
>>         > "Keep it Simple"
>>         >
>>         > _______________________________________________
>>         > forge-dev mailing list
>>         > forge-dev at lists.jboss.org <mailto:forge-dev at lists.jboss.org>
>>
>>         > https://lists.jboss.org/mailman/listinfo/forge-dev
>>         >
>>         >
>>         > _______________________________________________
>>         > forge-dev mailing list
>>         > forge-dev at lists.jboss.org <mailto:forge-dev at lists.jboss.org>
>>
>>         > https://lists.jboss.org/mailman/listinfo/forge-dev
>>
>>        /max
>>        http://about.me/maxandersen
>>
>>
>>
>>
>>        _______________________________________________
>>        forge-dev mailing list
>>        forge-dev at lists.jboss.org <mailto:forge-dev at lists.jboss.org>
>>
>>        https://lists.jboss.org/mailman/listinfo/forge-dev
>>
>>
>>
>>    _______________________________________________
>>    forge-dev mailing list
>>    forge-dev at lists.jboss.org <mailto:forge-dev at lists.jboss.org>
>>
>>    https://lists.jboss.org/mailman/listinfo/forge-dev
>>
>>
>>
>>
>> --
>> Lincoln Baxter, III
>> http://ocpsoft.com
>> http://scrumshark.com
>> "Keep it Simple"
>>
>
>
> --
> - DML
>



-- 
Lincoln Baxter, III
http://ocpsoft.com
http://scrumshark.com
"Keep it Simple"
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