The previous implementation had some slightly questionable memory safety
properties (older versions of PyO3 didn't uphold the Rust aliasing rules
and would thus create multiple &mut references to #[pyclass] objects).
This explains why Backend has internal Mutex<T>s even though all of its
methods took &mut self.
The solution is to simply make all methods take &self, which luckily
doesn't pose too make issues -- most of the code inside Backend already
has sufficient locking. The only two things which needed to be
explicitly handled where:
1. "self.runtime" which was fairly easy to handle. All usages of
the Runtime only require an immutable reference to create a new
Handle, so we could switch to OnceCell which provides
lazy-initialisation semantics without needing a more heavy-handed
Mutex<tokio::runtime::Handle>.
2. "self.sync_abort" was simply wrapped in a Mutex<>, though some of the
odd semantics of sync_abort (not being able to handle multiple
processes synchronising at the same time) become pretty obvious with
this change (for now we just log a warning in that case). In
addition, switch to an RAII-style guard to make sure we don't forget
to clear the abort_handle.
As a result, we now no longer break Rust's aliasing rules and we can
build with newer versions of PyO3 which have runtime checks for these
things (and build on stable Rust).
Signed-off-by: Aleksa Sarai <cyphar@cyphar.com>
prost-build doesn't generate rustfmt-safe code, so we had to add it to
the ignore list for rustfmt on "make check". However, the ignore list
isn't supported by stable rustfmt, so we have to work around this some
other way -- in this case, just do "rustfmt" on the generated file in
"build.rs" (this way, formatting errors in checked-in source code are
still caught but generated code doesn't cause spurrious errors).
Signed-off-by: Aleksa Sarai <cyphar@cyphar.com>
Allows add-ons to easily override the theme, and allows us to apply
styling to elements outside of the normal document flow (like applying
the normal background colour to a position: fixed element).
