On Mon, 10 Mar 2025 08:48:53 GMT, John Hendrikx <[email protected]> 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
