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From "Aleksey Ignatenko (JIRA)" <j...@apache.org>
Subject [jira] Commented: (HARMONY-3462) [dlrvm] new j.l.Class tracing model
Date Wed, 21 Mar 2007 13:02:32 GMT

    [ https://issues.apache.org/jira/browse/HARMONY-3462?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel#action_12482747

Aleksey Ignatenko commented on HARMONY-3462:

Checked with GCv4.1 and GCv5.

Importent! - GCv5 specifics:
GCv5 does not implement gc_add_weak_root_set_entry function (used in vm_enumerate_weak_root_reference).
Therefore enumeration as weak reference is not available.
For the first sight it is not to be able to work with GCv5, But drlvm redirects gc_add_weak_root_set_entry
fucntion to default one which is gc_add_root_set_entry (as a result j.l.Classes are always
reachable - added to rootset as strong references + traced by GC via j.l.Classloader), therefore
GCv5 works fine with the patch, but class unloading is not implementable on it untill it supports
gc_add_weak_root_set_entry function.

> [dlrvm] new j.l.Class tracing model
> -----------------------------------
>                 Key: HARMONY-3462
>                 URL: https://issues.apache.org/jira/browse/HARMONY-3462
>             Project: Harmony
>          Issue Type: Improvement
>          Components: DRLVM
>            Reporter: Aleksey Ignatenko
>         Attachments: new_class_registry_v7.patch
> The jira introduces new model of j.l.Class referencing into drlvm.
> The current model is:
> all j.l.Classes (JLC) and j.l.Classloaders (JLCL) are enumerated as strong references
inside drlvm. It means that all JLC and JLCL are always reachable and we can not track any
referencing between classes and classloaders automatically by GC.
> The new model is required by clas unloading (independent of class unloading design).
Lets name term "class registry" as -  JLCL refers to its JLC and JLC refer to their defining
JLCL (phisically via valid references). This requirement comes from the statement that classloader
and all classes loaded by it are to be unloaded at once. e.g. Robin-Salikh approach requires
that only JLCL are enumerated then JLC are to be traced automatically by GC (via references
in appropriate JLCL - right now there is no direct reference to JLC in JLCL and vice versa).

> The patch new_class_registry_v7.patch introduces the direct references described above.
Also, it changes enumeration model: from now all JLC are traced via JLCL. JLC references are
enumerated as weak references now (to be updated by GC).
> Also destination of m_loadedClasses and m_reportedClasses has changed. For now m_loadedClasses
is responsible for weak enumeration of all loaded UserDefined j.l.Classes and m_reportedClasses
is responsible for enumeration of all bootstrap classes and userdefined classes (untill they
are added to class registry)

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