[jira] [Commented] (MNG-6575) make Dependency immutable

["Yann Dameron (JIRA)" <ji...@apache.org>]

    [ https://issues.apache.org/jira/browse/MNG-6575?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16766534#comment-16766534 ] 

Yann Dameron commented on MNG-6575:
-----------------------------------

Hi guys,

I'm new on Maven source code but make Dependency immutable looks like a massive change and like Robert I don't get how we can do that without impacting signatures, existing plugins, etc.

As I reported the memory issues, I tried to find a solution to evaluate the memory gain using wrappers.

I added a class which is responsible of caching all the Dependency objects

I created a DependencyWrapper class which extends Dependency and takes a Dependency object in the constructor (the original one, which comes from the cache).
This class overrides all methods. As long as modifiers are not called, all the getters redirect to the original dependency. 
As soon as a setter is called, original dependency is nullified and the DependencyWrapper class behaves like the Dependency one...

Finally, I modified the mdo to use this cache and wrappers.
 * BaseModel.setDependencies
 * DependencyManagement.setDependencies
 * ModelMerger.mergeModelBase_Dependencies
 * ModelMerger.mergeDependencyManagement_Dependencies

I know I missed some places, (for example if DependencyManagement.addDependency is called, the cache and wrappers will not be used) but it was a basic attempt to evaluate the memory gain and prevent API changes.

Doing that, the memory dump is reduced to 3.5Gb (8Gb with MNG-6571 fix, 12Gb with maven 3.6.0).

Do you think it's worth creating a patch for review and improvements ? I appreciate this approach could be a blocker so just let me know :)

> make Dependency immutable
> -------------------------
>
>                 Key: MNG-6575
>                 URL: https://issues.apache.org/jira/browse/MNG-6575
>             Project: Maven
>          Issue Type: Improvement
>          Components: Dependencies, Inheritance and Interpolation
>    Affects Versions: 3.6.0
>            Reporter: Hervé Boutemy
>            Priority: Major
>
> while working on Maven memory consumption issue MNG-6571, once VersionRange is made immutable, memory used was divided by 2: the next big expected win is to make Dependency immutable, which would probably once again divide memory by 2 because the vast majority of time, dependencies (be it in dependencyManagement or base dependencies) are inherited without any modification
> this will require to change [ModelMerger|https://maven.apache.org/ref/3.6.0/maven-model/apidocs/org/apache/maven/model/merge/ModelMerger.html] 's {{mergeDependency(Dependency target, Dependency source, boolean sourceDominant, Map<Object,Object> context)}} signature, since is not really an immutable friendly signature
> and also make [Dependency code|https://maven.apache.org/ref/3.6.0/maven-model/apidocs/org/apache/maven/model/Dependency.html] immutable (generated by Modello)



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