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Date: Wed, 26 Jul 2017 16:57:49 +0200
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Subject: Don't add simple objects to GC's roots
From: nicolas.grekas@gmail.com (Nicolas Grekas)

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Hi,

I'm hitting more and more the GC threshold in projects I work on (the "10k
roots" one), leading to high CPU usage. Usually, the GC finds nothing to
clean, so this is just a waste of CPU.

By being super light and fast, objects are nice for many tasks, and the
trend is to use them all over the place, e.g. as nodes when parsing a PHP
AST.

There is a way to work around: just call gc_disable(). But this means
dealing with side effects of the engine in userland. Moreover, this also
means leaking memory, since meanwhile roots are not populated.

I was wondering: does it exist some light algorithm that could prevent
hitting the threshold that often?
E.g. in my previous example, AST nodes are created free of any circular
refs. Would it be possible to add them (and any objects really) to GC's
roots list *only* when userland does something that *might* create a
circular ref? (e.g. setting a property to a non scalar? or something more
clever?)

Just raising the topic, as unfortunately I wouldn't be able to do more.

Thanks for considering,
Nicolas

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