On Mon, 17 Feb 2025 15:37:56 GMT, John Hendrikx <[email protected]> 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 fix for regression :)
Regarding vetoing, I noticed that only the first registered listener can veto
since it overrides any subsequent value set.
Suppose listener A changes the value to 5, B changes it to 6, C changes it to
7, and Z does nothing, then upon setting a value from 0 to 1 we will see:
A sees 0->1; sets to 5
A sees 1->5
B sees 0->5; sets to 6
A sees 5->6; sets to 5
A sees 6->5
C got 0->5; sets to 7
A sees 5->7; sets to 5
A sees 7->5
Z sees 0->5
Is this intended?
-------------
PR Comment: https://git.openjdk.org/jfx/pull/1081#issuecomment-2664306130
