RFR: 8290310: ChangeListener events are incorrect or misleading when a nested change occurs [v7]

[Nir Lisker]

On Wed, 5 Mar 2025 18:27:29 GMT, John Hendrikx <jhendrikx at openjdk.org> wrote:

>> This provides and uses a new implementation of `ExpressionHelper`, called `ListenerManager` with improved semantics.
>> 
>> # Behavior
>> 
>> |Listener...|ExpressionHelper|ListenerManager|
>> |---|---|---|
>> |Invocation Order|In order they were registered, invalidation listeners always before change listeners|(unchanged)|
>> |Removal during Notification|All listeners present when notification started are notified, but excluded for any nested changes|Listeners are removed immediately regardless of nesting|
>> |Addition during Notification|Only listeners present when notification started are notified, but included for any nested changes|New listeners are never called during the current notification regardless of nesting|
>> 
>> ## Nested notifications:
>> 
>> | |ExpressionHelper|ListenerManager|
>> |---|---|---|
>> |Type|Depth first (call stack increases for each nested level)|(same)|
>> |# of Calls|Listeners * Depth (using incorrect old values)|Collapses nested changes, skipping non-changes|
>> |Vetoing Possible?|No|Yes|
>> |Old Value correctness|Only for listeners called before listeners making nested changes|Always|
>> 
>> # Performance
>> 
>> |Listener|ExpressionHelper|ListenerManager|
>> |---|---|---|
>> |Addition|Array based, append in empty slot, resize as needed|(same)|
>> |Removal|Array based, shift array, resize as needed|(same)|
>> |Addition during notification|Array is copied, removing collected WeakListeners in the process|Appended when notification finishes|
>> |Removal during notification|As above|Entry is `null`ed (to avoid moving elements in array that is being iterated)|
>> |Notification completion with changes|-|Null entries (and collected WeakListeners) are removed|
>> |Notifying Invalidation Listeners|1 ns each|(same)|
>> |Notifying Change Listeners|1 ns each (*)|2-3 ns each|
>> 
>> (*) a simple for loop is close to optimal, but unfortunately does not provide correct old values
>> 
>> # Memory Use 
>> 
>> Does not include alignment, and assumes a 32-bit VM or one that is using compressed oops.
>> 
>> |Listener|ExpressionHelper|ListenerManager|OldValueCaching ListenerManager|
>> |---|---|---|---|
>> |No Listeners|none|none|none|
>> |Single InvalidationListener|16 bytes overhead|none|none|
>> |Single ChangeListener|20 bytes overhead|none|16 bytes overhead|
>> |Multiple listeners|57 + 4 per listener (excluding unused slots)|57 + 4 per listener (excluding unused slots)|61 + 4 per listener (excluding unused slots)|
>> 
>> # About nested changes
>> 
>> Nested changes are simply changes...
>
> John Hendrikx has updated the pull request incrementally with one additional commit since the last revision:
> 
>   Fix docs

I tested the new convergence check. If listener A and listener B fight over a value, it works, but if I add after then listener C that just prints what it sees without changing the value, it completes without an error.

Is it not possible to let the SOE be thrown naturally (by infinite recursion)?

> Note that the non-convergence detection logic is pretty smart, as the test case where multiple listeners are trying to agree upon a value that is divisible by 3, 5, 7 and 11 still works fine

And what about non-integer values, like custom objects or strings?

-------------

PR Comment: https://git.openjdk.org/jfx/pull/1081#issuecomment-2702676397