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<p>Hi Andy,</p>
<p>Those examples seem to be just timers, it would be hard to
construct the primitives like throttle and debounce with these, as
they don't take into account when the value last changed, or
whether or not is important that the value changed again (reset
timer or not). These timers would just run forever, while the
functionality I propose here would have no timers running when
things are stable. The timeout would also trigger precisily on the
first value change. Having a running timer is more like sampling,
not throttling or debouncing.<br>
</p>
<p>The functionality I'm proposing would be more along the lines of
#reduceSucessions in
<a class="moz-txt-link-freetext" href="https://github.com/TomasMikula/ReactFX/blob/master/reactfx/src/main/java/org/reactfx/EventStream.java">https://github.com/TomasMikula/ReactFX/blob/master/reactfx/src/main/java/org/reactfx/EventStream.java</a>
-- except that it would never support accumulation or combining of
values (that's something for streams, not for values).</p>
<p>--John</p>
<div class="moz-cite-prefix">On 03/04/2023 18:47, Andy Goryachev
wrote:<br>
</div>
<blockquote type="cite"
cite="mid:DM5PR1001MB2172DF5CB8DCC167B4191DE0E5929@DM5PR1001MB2172.namprd10.prod.outlook.com">
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<p class="MsoNormal"><span
style="font-size:11.0pt;font-family:"Courier New"">My
two cents: I think the functionality of debouncing should
better be solved by a separate facility, rather than added
to observables. An example would be a use case when
multiple observables trigger an expensive or delayed
computation or a UI update.<o:p></o:p></span></p>
<p class="MsoNormal"><span
style="font-size:11.0pt;font-family:"Courier New""><o:p> </o:p></span></p>
<p class="MsoNormal"><span
style="font-size:11.0pt;font-family:"Courier New"">Something
along the lines of<o:p></o:p></span></p>
<p class="MsoNormal"><span
style="font-size:11.0pt;font-family:"Courier New""><a
href="https://github.com/TomasMikula/ReactFX/blob/master/reactfx/src/main/java/org/reactfx/util/FxTimer.java"
moz-do-not-send="true" class="moz-txt-link-freetext">https://github.com/TomasMikula/ReactFX/blob/master/reactfx/src/main/java/org/reactfx/util/FxTimer.java</a><o:p></o:p></span></p>
<p class="MsoNormal"><span
style="font-size:11.0pt;font-family:"Courier New"">or
<o:p>
</o:p></span></p>
<p class="MsoNormal"><span
style="font-size:11.0pt;font-family:"Courier New""><a
href="https://github.com/andy-goryachev/FxEditor/blob/master/src/goryachev/fx/FxTimer.java"
moz-do-not-send="true" class="moz-txt-link-freetext">https://github.com/andy-goryachev/FxEditor/blob/master/src/goryachev/fx/FxTimer.java</a><o:p></o:p></span></p>
<p class="MsoNormal"><span
style="font-size:11.0pt;font-family:"Courier New""><o:p> </o:p></span></p>
<p class="MsoNormal"><span
style="font-size:11.0pt;font-family:"Courier New"">cheers,<o:p></o:p></span></p>
<p class="MsoNormal"><span
style="font-size:11.0pt;font-family:"Courier New"">-andy<o:p></o:p></span></p>
<p class="MsoNormal"><span
style="font-size:11.0pt;font-family:"Courier New""><o:p> </o:p></span></p>
<p class="MsoNormal"><span
style="font-size:11.0pt;font-family:"Courier New""><o:p> </o:p></span></p>
<p class="MsoNormal"><span
style="font-size:11.0pt;font-family:"Courier New""><o:p> </o:p></span></p>
<div style="border:none;border-top:solid #B5C4DF
1.0pt;padding:3.0pt 0in 0in 0in">
<p class="MsoNormal" style="margin-bottom:12.0pt"><b><span
style="font-size:12.0pt;color:black">From:
</span></b><span style="font-size:12.0pt;color:black">openjfx-dev
<a class="moz-txt-link-rfc2396E" href="mailto:openjfx-dev-retn@openjdk.org"><openjfx-dev-retn@openjdk.org></a> on behalf of Marius
Hanl <a class="moz-txt-link-rfc2396E" href="mailto:mariushanl@web.de"><mariushanl@web.de></a><br>
<b>Date: </b>Thursday, March 30, 2023 at 15:20<br>
<b>To: </b>John Hendrikx <a class="moz-txt-link-rfc2396E" href="mailto:john.hendrikx@gmail.com"><john.hendrikx@gmail.com></a><br>
<b>Cc: </b><a class="moz-txt-link-abbreviated" href="mailto:openjfx-dev@openjdk.org">openjfx-dev@openjdk.org</a>
<a class="moz-txt-link-rfc2396E" href="mailto:openjfx-dev@openjdk.org"><openjfx-dev@openjdk.org></a><br>
<b>Subject: </b>Aw: Gauging interest in bindings that can
delay changing their value (debounce/throttle)<o:p></o:p></span></p>
</div>
<div>
<div>
<p class="MsoNormal"><span
style="font-size:9.0pt;font-family:"Verdana",sans-serif">+
1 for this. Debouncing is a common functionality for
observables.<o:p></o:p></span></p>
</div>
<div>
<p class="MsoNormal"><span
style="font-size:9.0pt;font-family:"Verdana",sans-serif">One
of the common scenarios is obviously something like a
search filter functionality, where typing in characters
triggers an expensive calculation.<o:p></o:p></span></p>
</div>
<div>
<p class="MsoNormal"><span
style="font-size:9.0pt;font-family:"Verdana",sans-serif">Debouncing
solves the problem by doing that when nothing happened
for some time, which is typically met when the user
finished typing.<o:p></o:p></span></p>
</div>
<div>
<p class="MsoNormal"><span
style="font-size:9.0pt;font-family:"Verdana",sans-serif"> <o:p></o:p></span></p>
</div>
<div>
<p class="MsoNormal"><span
style="font-size:9.0pt;font-family:"Verdana",sans-serif">--
Marius<o:p></o:p></span></p>
</div>
<div>
<p class="MsoNormal"><span
style="font-size:9.0pt;font-family:"Verdana",sans-serif">
<o:p></o:p></span></p>
<div>
<p class="MsoNormal"><span
style="font-size:9.0pt;font-family:"Verdana",sans-serif">
<o:p></o:p></span></p>
<div style="border:none;border-left:solid #C3D9E5
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<div style="margin-bottom:7.5pt">
<p class="MsoNormal"><b><span
style="font-size:9.0pt;font-family:"Verdana",sans-serif">Gesendet:</span></b><span
style="font-size:9.0pt;font-family:"Verdana",sans-serif"> Donnerstag,
23. März 2023 um 18:09 Uhr<br>
<b>Von:</b> "John Hendrikx"
<a class="moz-txt-link-rfc2396E" href="mailto:john.hendrikx@gmail.com"><john.hendrikx@gmail.com></a><br>
<b>An:</b> <a class="moz-txt-link-abbreviated" href="mailto:openjfx-dev@openjdk.org">openjfx-dev@openjdk.org</a><br>
<b>Betreff:</b> Gauging interest in bindings that
can delay changing their value (debounce/throttle)<o:p></o:p></span></p>
</div>
<div name="quoted-content">
<p class="MsoNormal"><span
style="font-size:9.0pt;font-family:"Verdana",sans-serif">Hi
list,<br>
<br>
I've been working on a potential new API (and
proof of concept<br>
implementation) for adding a new type of fluent
binding which can delay<br>
changing their values, and I'm wondering how much
interest there is in<br>
such a thing.<br>
<br>
The main purpose of such an API is to prevent
being flooded with changes<br>
when properties change often, or to simply delay
certain actions until<br>
the user has settled on a selection or has stopped
typing.<br>
<br>
For this purpose I would like to introduce a
default method on<br>
`ObservableValue` with the signature:<br>
<br>
ObservableValue<T> throttle(Throttler
throttler);<br>
<br>
The parameter `Throttler` can be obtained via
static methods of a helper<br>
class named `FXThrottlers`. These provide various
pre-configured<br>
throttlers that work correctly with JavaFX's event
thread model. My<br>
current proof of concept provides:<br>
<br>
public static Throttler debounce(Duration
quietPeriod);<br>
public static Throttler
debounceTrailing(Duration quietPeriod);<br>
public static Throttler throttle(Duration
period);<br>
public static Throttler
throttleTrailing(Duration period);<br>
<br>
These are variations of similar concepts, and vary
mostly in when<br>
exactly they will allow value changes; debouncers
will wait for a period<br>
without any changes, while throttlers will
periodically allow changes.<br>
The trailing variants will not immediately emit
the first change but<br>
will wait for the period to elapse first; all
variants will eventually<br>
take on the value of the source observable.
Debouncing is typically<br>
used when you wish for an input to settle before
taking action (like<br>
typing in a search bar), while throttling is used
to give regular<br>
feedback but avoid doing so too often (like
feedback during window<br>
resizing).<br>
<br>
Usage example which updates a preview panel when
the user has finished<br>
(cursor) scrolling through a list view:<br>
<br>
ObjectProperty<T> selectedItem =<br>
listView.getSelectionModel().selectedItemProperty();<br>
<br>
selectedItem<br>
.throttle(FXThrottlers.debounceTrailing(Duration.ofMillis(500)))<br>
.addListener((obs, old, current) -> {<br>
if (current != null) {<br>
updatePreviewPanel(current);<br>
}<br>
});<br>
<br>
Implementation details:<br>
<br>
ObservableValue is part of javafx.base, and as
such can't use animations<br>
or call Platform::runLater. The ThrottledBinding
implementation has<br>
abstracted all of these out into the Throttler
class, and FXThrottlers<br>
(which would live in javafx.graphics) therefore
provides the necessary<br>
call backs to integrate property changes correctly
back onto the JavaFX<br>
event thread. The Throttler class also simplifies
testing; the test can<br>
provide its own timing source and background
scheduler. The Throttler<br>
interface has the following methods:<br>
<br>
/**<br>
* Schedules a command to run on an
unspecified thread after the time<br>
* given by {@code nanos} elapses.<br>
*<br>
* @param command a command to run, cannot be
{@code null}<br>
* @param nanos a time in nanoseconds<br>
*/<br>
void schedule(Runnable command, long nanos);<br>
<br>
/**<br>
* Provides the current time in nanoseconds.<br>
*<br>
* @return the current time in nanoseconds<br>
*/<br>
long nanoTime();<br>
<br>
/**<br>
* Runs the given command as soon as possible
on a thread specified<br>
by this<br>
* throttler for updating property values.<br>
*<br>
* @param command a command to run, cannot be
{@code null}<br>
*/<br>
void update(Runnable command);<br>
<br>
/**<br>
* Given the current elapsed time in the
current change window, and the<br>
* amount of time elapsed since the last
change was detected,<br>
determines<br>
* if and by how much the current change
window should be extended.<br>
*<br>
* @param elapsed nanoseconds elapsed since
the start of the<br>
current change window<br>
* @param elapsedSinceLastChange nanoseconds
elapsed since the last<br>
change<br>
* @return nanoseconds to extend the window
with<br>
*/<br>
long determineInterval(long elapsed, long
elapsedSinceLastChange);<br>
<br>
For testing purposes, the schedule and nanoTime
can be provided such<br>
that the throttle function can be tested
deterministically. For<br>
integrating with JavaFX, update is implemented as<br>
`Platform.runLater(command)`. The schedule and
nanoTime methods<br>
delegate to an Executor and System.nanoTime
respectively. When using<br>
properties without JavaFX, Throttler
implementations can be provided<br>
which run property updates on a scheduler thread
(just calling<br>
Runnable::run on the current thread) or via some
user provided executor.<br>
<br>
A sample test case looks like this (read with a
mono space font :-)):<br>
<br>
@Test<br>
void testThrottleLeadingAndTrailing() {<br>
// create Throttler with deterministic
behavior:<br>
Throttler throttler =<br>
create(Throttler.IntervalHandler.throttle(Duration.ofNanos(4));<br>
<br>
// create throttled observable:<br>
ObservableValue<String> binding =
source.throttle(throttler);<br>
<br>
assertChanges(<br>
binding,<br>
"--a-b--c---d-----e-------f-g-----------f-g-----",<br>
"--a---b---c---d---e------f---g---------f---g---"<br>
);<br>
<br>
assertInvalidations(<br>
binding,<br>
"--a-b--c---d-----e-------f-g-----------f-g-----",<br>
"--i---i---i---i---i------i---i---------i---i---"<br>
);<br>
}<br>
<br>
Thanks for reading, I look forward to your
feedback!<br>
<br>
--John<br>
<br>
<br>
<br>
<o:p></o:p></span></p>
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