Mark arrays as collectable at runtime #9979
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Arrays are now marked with GC_NOT_COLLECTABLE by default. Only objects and references can actually contribute to a cycle. Once an object or reference is added to the array the GC_NOT_COLLECTABLE flag is removed. This patch does never re-add the flag when the potentially cyclic element is removed. This would be possible but would require tracking the number of potentially elements on override/remove.
iluuu1994
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I tried benchmarking with Valgrind as well as with Symfony Demo /
Symfony Demo /de/blog/:
PHPStan |
| static zend_always_inline bool gc_ht_check_collectable(HashTable *ht) { | ||
| return (GC_FLAGS(ht) & (GC_PERSISTENT|GC_NOT_COLLECTABLE)) == GC_NOT_COLLECTABLE; | ||
| } |
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The name of the function is confusing. It doesn't tell what kind of check we do (positive or negative). I would propose to change it into gc_ht_is_not_collectable() or may be better into gc_ht_is_collectable() with corresponding condition changes.
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It looks like the current implementation doesn't make significant effect. Some apps become a bit faster others are slower. I think we should postpone this and think about non-collectable objects first. After disabling creation of dynamic object properties (they are deprecated in PHP-8.2) we may determine non-collectable classes just analysing their properties. Then it would make sense to adopt Also the GC algorithm might be improved. See the related ideas described at http://www.eng.usf.edu/~chang5/papers/12/RC_chang_12.pdf |
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@dstogov Thank you for taking the time to review this. That works for me, let's postpone this and see if it works better in combination with non-collectable objects, which won't require flagging at runtime. |
Arrays in this PR are marked with GC_NOT_COLLECTABLE by default. In arrays, only objects and references can actually contribute to a cycle because cycles with just arrays are impossible to create from userland. Once an object or reference is added to the array the GC_NOT_COLLECTABLE flag is removed. This patch does not re-add the flag when the potentially cyclic element is removed. This would be possible but would require tracking the number of elements on override/remove.
Benchmarks are yet to be done. This touches several hot-paths so we'll need to make sure it's worth it. JIT also needs an adjustment in one of the handlers which I'll look into. @dstogov I'd be very glad to hear your general thoughts before continuing to avoid working on something potentially non-feasible.
Btw, something similar might be possible for objects once dynamic properties gets fully removed.
When:
then the object of the given class doesn't need to be added to the gc buffer. The two could also be combined, meaning non-cyclic classes added to arrays can't make the arrays cyclic.