@nullOut annotation #10959
@nullOut annotation #10959
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😎🆒 |
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I don't understand Seth's emojis so ❤️ and 🚀. |
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I took another look at
scala> val ll: LazyList[Int] = 1 #:: 2 #:: 3 #:: ll
val ll: LazyList[Int] = LazyList(<not computed>)
scala> ll.mkString
val res0: String = 123<cycle>Even though that could be considered an inconsistency, it seems desired (scala/collection-strawman#550, scala/bug#8680). Cycle detection uses the 2x/1x iterator idea (Floyd's Algorithm). So for a very long non-cyclic LazyList, the slow pointer points to the middle of the list when the fast one reaches the end. So at least half of the list cannot be GC'd. I don't see how we could fix it. |
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@-ing @NthPortal and @scala/collections |
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Hello, optimizer! |
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`this: @nullOut` or `local: @nullOut` sets the local variable slot to `null` after loading the value on the stack. Mixin forwarders, static mixin accessors and bridges set the receiver local to `null` if the target method is annotated `@nullOut`, for example. Co-authored-by: Stefan Zeiger <[email protected]>
Needs a restarr to work! The forwarder / alias `IterableOnceOps./:` uses `@nullOut` to clear the `this` reference before calling `foldLeft`. The annotation is also on the method itself to ensure mixin forwarders (generated in the subclass) and the static mixin accessor (generated in the trait) null out the receiver before invoking `/:`. After removing `LazyList.foldLeft`, it inherits the implementation from LinearSeqOps. That method again uses `@nullOut` twice, once to clear `this` when it's no longer needed, and once on the method for the generated accessors. I think we should *not* use `@nullOut` everywhere in the standard library, only on methods that cannot be overridden in LazyList, like `/:`. `@nullOut` works correctly on `mkString` too, but unfortunately the `addString` override in LazyList prevents GC of processed elements due to cycle detection.
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Includes changes from #10937.
Continuation of #7990.
this: @nullOutorlocal: @nullOutsets the local variable slot tonullafter loading the value on the stack.Mixin forwarders, static mixin accessors and bridges set the receiver
local to
nullif the target method is annotated@nullOut.As a test, use
@nullOutfor the forwarder / aliasIterableOnceOps./:.It uses
@nullOutto clearthe
thisreference before callingfoldLeft. The annotation isalso on the method itself to ensure mixin forwarders (generated in
the subclass) and the static mixin accessor (generated in the trait)
null out the receiver before invoking
/:.After removing
LazyList.foldLeft, it inherits the implementationfrom LinearSeqOps. That method again uses
@nullOuttwice, onceto clear
thiswhen it's no longer needed, and once on the methodfor the generated accessors.
I think we should not use
@nullOuteverywhere in the standardlibrary, only on methods that cannot be overridden in LazyList.
So, for final methods like
/:ormkString.