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Ruby <2.7now uses WeakMap too, which prevents memory leaks. #8341

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merged 1 commit into from Feb 25, 2021

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Ruby <2.7 does not allow non-finalizable objects to be WeakMap
keys: https://bugs.ruby-lang.org/issues/16035

We work around this by using a secondary map for Ruby <2.7 which
maps the non-finalizable integer to a distinct object.

For now we accept that the entries in the secondary map wil never
be collected. If this becomes a problem we can perform a GC pass
every so often that looks at the contents of the object cache to
decide what can be deleted from the secondary map.

This also changes the way that object pinning works. We pin objects
when they are frozen so they do not forget their frozen state.
Now we implement this with a simple array in Arena, instead of
making it part of the object cache.

Fixes: #8337

Ruby <2.7 does not allow non-finalizable objects to be WeakMap
keys: https://bugs.ruby-lang.org/issues/16035

We work around this by using a secondary map for Ruby <2.7 which
maps the non-finalizable integer to a distinct object.

For now we accept that the entries in the secondary map wil never
be collected.  If this becomes a problem we can perform a GC pass
every so often that looks at the contents of the object cache to
decide what can be deleted from the secondary map.
@haberman
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haberman commented Feb 25, 2021

Besides not leaking memory any more, this PR also runs the unit tests faster for Ruby 2.5. So I expect improved performance for Rubies prior to 2.7.

@haberman haberman merged commit 80ec787 into protocolbuffers:3.15.x Feb 25, 2021
This was referenced Mar 12, 2021
@haberman haberman deleted the ruby-2.5-gc branch April 20, 2021 18:43
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3 participants