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https://issues.apache.org/jira/browse/FLINK-21419?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17301408#comment-17301408
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Kezhu Wang commented on FLINK-21419:
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Glad to see, we all lean to fail concurrent free by default, at least in dev. I
guess core dump is most notable and destructive failure:(. I tried to throw
exception in my local env, it does not work at least for FLINK-21728 as many
exceptions are just swallowed in closing phase. I think we could write some
code to print stack traces if concurrent free detected just like [~xintongsong]
has do in FLINK-21728.
{quote}the original purpose of using GC cleaner was to rely on both explicit
segment free and GC for releasing the memory, while make sure the memory is
released only once.
{quote}
I actually tracked this story a bit in weekend. This changed in
FLINK-14894(superseded by FLINK-15758 later) where there is a conclusion at
that time:
{quote}The conclusion at the moment is that release unsafe memory, while
potentially having link on it in Java code, is dangerous.
{quote}
The fact does not changed.
I list existing options here:
* Rely on manually free and safety net for leaking detection. We are currently
going this way. It is also adopted before FLINK-14894. It might be dangerous if
there are mistakes in free timing.
* Totally rely on gc to reclaim native memory. It is adopted in FLINK-15758.
This is the safest version but the reclaiming is not as instant as manual
counterpart.
I like #1, but the diagnosis/fix to potential mistake could be time consuming.
I wonder wether we could combine the two by introducing an option to switch
between. So that if bad things happen in #1, users could circumvent it through
#2 for a while.
If we are going solely #1, I also think {{finalize}} should match our target.
> Remove GC cleaner mechanism for unsafe memory segments
> ------------------------------------------------------
>
> Key: FLINK-21419
> URL: https://issues.apache.org/jira/browse/FLINK-21419
> Project: Flink
> Issue Type: Sub-task
> Components: Runtime / Coordination
> Reporter: Xintong Song
> Assignee: Nicholas Jiang
> Priority: Major
> Labels: pull-request-available
> Fix For: 1.13.0
>
>
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