RFR: 8290310: ChangeListener events are incorrect or misleading when a nested change occurs [v12]

[Michael Strauß]

On Mon, 10 Mar 2025 08:48:53 GMT, John Hendrikx <jhendrikx at openjdk.org> wrote:

>> This provides and uses a new implementation of `ExpressionHelper`, called `ListenerManager` with improved semantics.
>> 
>> See also #837 for a previous attempt which instead of triggering nested emissions immediately (like this PR and `ExpressionHelper`) would wait until the current emission finishes and then start a new (non-nested) emission.
>> 
>> # 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 overhe...
>
> John Hendrikx has updated the pull request incrementally with three additional commits since the last revision:
> 
>  - Small fixes from review comments
>  - Use switch expression where reasonable
>  - Update docs regarding NullPointerExceptions

modules/javafx.base/src/main/java/com/sun/javafx/binding/ListenerList.java line 174:

> 172:                  */
> 173: 
> 174:                 throw new StackOverflowError("non-converging value detected in value modifying listeners on " + observableValue + "; original value was: " + oldValue);

We shouldn't throw errors, even if that's what the old implementation would implicitly do (not that it matters, no sane application would ever try to catch a `StackOverflowError` as part of its normal control flow). I think a `RuntimeException` is in order.

Also maybe make the message a bit clearer:
`<observableValue> was changed during the invocation of multiple listeners, but the new values diverge [original value: <oldValue>]`

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

PR Review Comment: https://git.openjdk.org/jfx/pull/1081#discussion_r1986911609