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Auto merge of #18386 - bholley:unchecked_cssom_get, r=upsuper

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Bypass the lock in get_property_value

This measurably improves performance - see https://bugzilla.mozilla.org/show_bug.cgi?id=1355599#c21

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This commit is contained in:
bors-servo 2017-09-05 23:20:55 -05:00 • committed by GitHub
commit e3568ba07a
2 changed files with 29 additions and 3 deletions
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7
components/style/shared_lock.rs
View file

@ -176,6 +176,13 @@ impl<T> Locked<T> {
}
}
/// Access the data for reading without verifying the lock. Use with caution.
#[cfg(feature = "gecko")]
pub unsafe fn read_unchecked<'a>(&'a self) -> &'a T {
let ptr = self.data.get();
&*ptr
}
/// Access the data for writing.
pub fn write_with<'a>(&'a self, guard: &'a mut SharedRwLockWriteGuard) -> &'a mut T {
assert!(self.same_lock_as(&guard.0),

25
ports/geckolib/glue.rs
View file

@ -1124,6 +1124,20 @@ fn read_locked_arc<T, R, F>(raw: &<Locked<T> as HasFFI>::FFIType, func: F) -> R
func(Locked::<T>::as_arc(&raw).read_with(&guard))
}
#[cfg(debug_assertions)]
unsafe fn read_locked_arc_unchecked<T, R, F>(raw: &<Locked<T> as HasFFI>::FFIType, func: F) -> R
where Locked<T>: HasArcFFI, F: FnOnce(&T) -> R
{
read_locked_arc(raw, func)
}
#[cfg(not(debug_assertions))]
unsafe fn read_locked_arc_unchecked<T, R, F>(raw: &<Locked<T> as HasFFI>::FFIType, func: F) -> R
where Locked<T>: HasArcFFI, F: FnOnce(&T) -> R
{
func(Locked::<T>::as_arc(&raw).read_unchecked())
}
fn write_locked_arc<T, R, F>(raw: &<Locked<T> as HasFFI>::FFIType, func: F) -> R
where Locked<T>: HasArcFFI, F: FnOnce(&mut T) -> R
{
@ -2263,9 +2277,14 @@ macro_rules! get_property_id_from_property {
fn get_property_value(declarations: RawServoDeclarationBlockBorrowed,
property_id: PropertyId, value: *mut nsAString) {
read_locked_arc(declarations, |decls: &PropertyDeclarationBlock| {
decls.property_value_to_css(&property_id, unsafe { value.as_mut().unwrap() }).unwrap();
})
// This callsite is hot enough that the lock acquisition shows up in profiles.
// Using an unchecked read here improves our performance by ~10% on the
// microbenchmark in bug 1355599.
unsafe {
read_locked_arc_unchecked(declarations, |decls: &PropertyDeclarationBlock| {
decls.property_value_to_css(&property_id, value.as_mut().unwrap()).unwrap();
})
}
}
#[no_mangle]