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Synchronize the change handlers

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I'm pretty confident that this isn't actually required by the JavaFX
threading model, but it makes the code more obviously correct and
uncontended synchronization has a negligible cost when we're talking
about UI-level changes.
This commit is contained in:
Sarah Gerweck 2015-08-10 19:09:03 -07:00
parent 3f30eb32c2
commit 13e841d613
1 changed files with 11 additions and 4 deletions
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15
src/main/scala/org/gerweck/scalafx/util/observable.scala
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@ -8,6 +8,13 @@ import scalafx.beans.property._
import scalafx.beans.value._ import scalafx.beans.value._
trait ObservableImplicits { trait ObservableImplicits {
/* NOTE: (Sarah) I believe that the synchronization in these helpers is not
* _really_ required in the JavaFX threading model. However, the overhead of
* uncontended synchronization is relatively low, and typical UIs won't have
* enough change events for it to be a serious issue. (If you're updating
* a property in a tight loop, I expect you'll have bigger performance
* issues.)
*/
implicit val observableInstances = new Applicative[Observable] with Functor[Observable] with Monad[Observable] { implicit val observableInstances = new Applicative[Observable] with Functor[Observable] with Monad[Observable] {
/* Map can be derived from `ap`, but this adds less overhead. */ /* Map can be derived from `ap`, but this adds less overhead. */
override def map[A, B](a: Observable[A])(f: A => B): ObservableValue[B, B] = { override def map[A, B](a: Observable[A])(f: A => B): ObservableValue[B, B] = {
@ -18,7 +25,7 @@ trait ObservableImplicits {
val prop = ObjectProperty[B](originalValue) val prop = ObjectProperty[B](originalValue)
var prevValue = originalValue var prevValue = originalValue
def changeHandler = { def changeHandler = prop.synchronized {
val newVal = recalculate() val newVal = recalculate()
if (prevValue != newVal) { if (prevValue != newVal) {
prop.value = recalculate() prop.value = recalculate()
@ -44,7 +51,7 @@ trait ObservableImplicits {
var prevValue = originalValue var prevValue = originalValue
def changeHandler = { def changeHandler = prop.synchronized {
val newVal = recalculate() val newVal = recalculate()
if (prevValue != newVal) { if (prevValue != newVal) {
prop.value = newVal prop.value = newVal
@ -74,7 +81,7 @@ trait ObservableImplicits {
var prevValue = originalValue var prevValue = originalValue
def innerHandle() = { def innerHandle() = prop.synchronized {
val newVal = calc() val newVal = calc()
if (prevValue != newVal) { if (prevValue != newVal) {
prop.value = newVal prop.value = newVal
@ -84,7 +91,7 @@ trait ObservableImplicits {
var innerSub = oa() onChange innerHandle var innerSub = oa() onChange innerHandle
var prevOuter = oa() var prevOuter = oa()
def outerHandle() = { def outerHandle() = prop.synchronized {
val newOuter = oa() val newOuter = oa()
/* We need reference equality here: we're subscribing to a specific object. */ /* We need reference equality here: we're subscribing to a specific object. */
if (prevOuter ne newOuter) { if (prevOuter ne newOuter) {