Wouldn't it be better to implement this check in assert to avoid any
impact in production?
No. Using an assert in a case like this is an anti-pattern. A call to
assert in a library such as JavaFX is only appropriate for checking an
invariant in internal logic. If we are going to go down this route of
doing a thread check when mutating properties of "live" nodes, we will
throw the same IllegalStateException that is currently thrown by some
methods on Stage and Scene.
As for the proposal itself, adding this check is an interesting idea. We
considered doing this back in the JDK 7 (JavaFX 2) time frame, but
decided not to pursue it then. I think the idea is worth further
discussion. I would limit any thread checking to setting the property.
It would be too restrictive (and largely unnecessary) to prevent reading
a property from the application thread.
The things to consider would be:
1. What is the performance hit of doing this check on the setting of
every property?
2. What is the effect on bound properties?
3. How intrusive is it in the code?
4. Should we add a property to enable / disable the thread check,
possibly a three- or four-valued property (allow|warn|debug?|deny), as
was recently done in JEP 471 for sun.misc.Unsafe memory access methods.
If so, what should the default be?
My quick take is that if this can be done in a minimally intrusive
manner with low overhead, we should consider pursing this. As for 4, my
preference would be to add a three- or four-valued system property to
control the check, with "warn" as the default initially, changing the
default to "disallow" in a subsequent version. This would, of course,
require a lot of testing.
-- Kevin
On 8/4/2024 8:40 PM, quizynox wrote:
Hello,
Wouldn't it be better to implement this check in assert to avoid any
impact in production?
пн, 5 авг. 2024 г. в 03:30, John Hendrikx <john.hendr...@gmail.com>:
Hi list,
I know of quite some bugs and users that have been bitten by the
threading model used by JavaFX. Basically, anything directly or
indirectly linked to an active Scene must be accessed on the FX
thread.
However, as FX also allows manipulating nodes and properties before
they're displayed, there can be no "hard" check everywhere to
ensure we
are on the FX thread (specifically, in properties).
Now, I think this situation is annoying, as a simple mistake where a
Platform.runLater wrapper was forgotten usually results in programs
operating mostly flawlessly, but then fail in mysterious and
random and
hard to reproduce ways. The blame is often put on FX as the
resulting
exceptions will almost never show the user code which was the actual
culprit. It can result in FX being perceived as unstable or buggy.
So I've been thinking if there isn't something we can do to detect
these
bugs originating from user code much earlier, similar to the
`ConcurrentModificationException` the collection classes do when
accessed in nested or concurrent contexts.
I think it may be possible to have properties check whether
they're part
of an active scene without too much of an performance impact,
possibly
even behind a switch. It would work like this:
Properties involved with Nodes will have an associated bean instance
(`getBean`). This is an object, but we could check here if this
instance implements an interface:
if (getBean() instanceof MayBePartOfSceneGraph x) {
if (x.isPartOfActiveScene() && !isOnFxThread()) {
throw new IllegalStateException("Property must
only be
used from the FX Application Thread");
}
}
This check could be done on every set of the property, and
potentially
on every get as well. It should be relatively cheap, but will expose
problematic code patterns at a much earlier stage. There's a chance
that this will "break" some programs that seemed to be behaving
correctly as well, so we may want to put it behind a switch until
such
programs (or libraries) can be fixed.
What do you all think?
--John
(*) Names of methods/interfaces are only used for illustration
purposes,
we can think of good names if this moves forward.
