On Fri, 10 Mar 2023 05:19:13 GMT, John Hendrikx <jhendr...@openjdk.org> wrote:
> Description copied from issue: > > There are up to two additional invalidations performed that really should be > avoided, causing downstream fluent bindings to be recomputed with the same > values. This is very confusing as these should only be called when there is > an actual change, and not called for the same value multiple times in a row. > > These two extra invalidations have two different causes, each causing an > additional invalidation to be triggered: > > 1) ObjectBinding's `isObserved` is delayed slightly. When you add a > listener, the listener is added internally and the binding is made valid; > this triggers some downstream activity which checks the `isObserved` status > to decide whether to start observation of properties -- unfortunately this > still returns `false` at that time. A work-around for this existed by > calling `getValue` again in `LazyObjectBinding` with a huge comment > explaining why this is needed. Although this works, it still means that a > downstream function like `map` is called an additional time while it should > really only be called once. > > The solution is to ensure `isObserved` returns `true` before the > `ExpressionHelper` is called. Already verified this solves the problem. > This also means the work-around in `LazyObjectBinding` is no longer needed, > which seems like a big win. > > 2) The second additional call originates from a different issue. When > `ConditionalBinding` (which implements the `when` construct) sees its > condition property changing, it always invalidates itself. This is however > only necessary if the current cached value (if it was valid) differs from the > current source value. To prevent an unnecessary invalidation, and the > resulting revalidation calls that this will trigger, a simple check to see if > the value actually changed before invalidating solves this problem. Looks good to me. modules/javafx.base/src/main/java/javafx/beans/binding/ObjectBinding.java line 66: > 64: private T value; > 65: private boolean valid = false; > 66: private boolean isObserved; Minor: "observed" might be more consistent with the field naming convention in this file. modules/javafx.base/src/test/java/test/javafx/beans/value/ObservableValueWhenTest.java line 1: > 1: package test.javafx.beans.value; This file is missing a copyright header. ------------- Marked as reviewed by mstrauss (Committer). PR Review: https://git.openjdk.org/jfx/pull/1056#pullrequestreview-1375304698 PR Review Comment: https://git.openjdk.org/jfx/pull/1056#discussion_r1160080910 PR Review Comment: https://git.openjdk.org/jfx/pull/1056#discussion_r1160079643
