On Thu, 1 Sep 2022 13:10:49 GMT, John Hendrikx <jhendr...@openjdk.org> wrote:
>> modules/javafx.base/src/main/java/javafx/beans/value/ObservableValue.java
>> line 266:
>>
>>> 264: * {@code condition} evaluates to {@code true}. This allows this
>>> {@code ObservableValue}
>>> 265: * and the conditional {@code ObservableValue} to be garbage
>>> collected if neither is
>>> 266: * otherwise strongly referenced when {@code condition} becomes
>>> {@code false}.
>>
>> What happens if they are GC'd and the conditional becomes `true` later?
>
> Edit: I missed some nuance, below is the correct version.
>
> There are three objects involved here: the parent observable, the new
> observable and the conditional.
>
> What `when` should achieve is to make the new observable and conditional easy
> to garbage collect when the conditional is `false` (the parent observable is
> considered to be long lived so GC doesn't really apply there). The
> conditional and new observable refer to each other so they must have a
> similar life cycle.
>
>> What happens if they are GC'd and the conditional becomes `true` later?
>
> This can't happen, the conditional refers to the new observable, their life
> cycles are tied to each other.
>
> Strong references look like this when conditional is `true`:
>
> conditional <--> new observable <--> parent observable
>
> When it is `false`:
>
> conditional <--> new observable --> parent observable
>
> Conditional must have a similar life cycle as new observable if your purpose
> is to use `when` to break strong references to allow for GC.
If I have a (dumb) method
void someMethod(ObservableValue<String> longLivedProperty) {
ObservableValue<Boolean> condition = new SimpleBooleanProperty(true);
ObservableValue<String> whenProperty = longLivedProperty.when(condition)
}
then shouldn't `condition` and `whenProperty` be eligible for GC even when
`condition` holds `true`? If not, do I not get a memory leak because I can't
change `condition` to `false` to allow garbage collection?
-------------
PR: https://git.openjdk.org/jfx/pull/830
