This cascaded into a lot more work than expected. However, in general,
if one clones a `WidgetInstance` and shares it between two windows, it
should now work. Widget authors must ensure that when they cache
information, they do so with either a `WidgetCacheKey` or use a
`WindowLocal<T>` if per-window state is desired.
This is demonstrated in the debug-window example, where the counter of
open windows is next to a clone of the same button from the main window
that opens a new window.
While this was a workaround for a docs.rs issue (Px/Lp are not
linked), I decided having the shorter import path would look better in
the examples.
It probably wasn't necessary to update all of the references in the
internal code, but I decided it was worth the consistency.
Closes#91
There's some details to still figure out, which are in new issues:
- #109: When opening a window, no handle is returned that gives access to the
window from the opener. Technically this can all be wired up manually,
with exception of requeesting the window close.
- #107: How can a window close itself? Once we have a handle type, we still
need a mechanism to allow a button on a window request that the window
closes gracefully. The examples that currently close the window
call exit instad.
This sounds like a regression, but it was masking a "race condition".
DynamicGuard runs the change callbacks on drop in a background thread.
Validations was using the guard to not have to lock twice.
This led to an issue where the invalid count might be non-zero due to
the callbacks not being invoked, preventing the closure from being
invoked even though there are no validation errors.
Introducing compare_swap gives a higher-level API for Validations to
use, and it also ensures the callbacks are able to be run in the current
thread.
