style: Add Gecko profiler labels for when the style threads are doing work.

Differential Revision: https://phabricator.services.mozilla.com/D30869

components/style/gecko/mod.rs

@@ -13,6 +13,8 @@ pub mod conversions;
 pub mod data;
 pub mod media_features;
 pub mod media_queries;
+#[cfg(feature = "gecko_profiler")]
+pub mod profiler;
 pub mod pseudo_element;
 pub mod restyle_damage;
 pub mod rules;

components/style/gecko/profiler.rs

@@ -0,0 +1,76 @@
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at https://mozilla.org/MPL/2.0/. */
+
+//! Gecko profiler support.
+//!
+//! Use the `profiler_label!` macro from macros.rs.
+
+use crate::gecko_bindings::structs;
+
+/// A label describing a category of work that style threads can perform.
+pub enum ProfilerLabel {
+    /// Style computation.
+    Style,
+    /// Style sheet parsing.
+    Parse,
+}
+
+/// RAII object that constructs and destroys a C++ AutoProfilerLabel object
+/// pointed to be the specified reference.
+#[cfg(feature = "gecko_profiler")]
+pub struct AutoProfilerLabel<'a>(&'a mut structs::AutoProfilerLabel);
+
+#[cfg(feature = "gecko_profiler")]
+impl<'a> AutoProfilerLabel<'a> {
+    /// Creates a new AutoProfilerLabel with the specified label type.
+    ///
+    /// unsafe since the caller must ensure that `label` is allocated on the
+    /// stack.
+    #[inline]
+    pub unsafe fn new(
+        label: &mut structs::AutoProfilerLabel,
+        label_type: ProfilerLabel,
+    ) -> AutoProfilerLabel {
+        let category_pair = match label_type {
+            ProfilerLabel::Style => structs::JS::ProfilingCategoryPair_LAYOUT_StyleComputation,
+            ProfilerLabel::Parse => structs::JS::ProfilingCategoryPair_LAYOUT_CSSParsing,
+        };
+        structs::Gecko_Construct_AutoProfilerLabel(label, category_pair);
+        AutoProfilerLabel(label)
+    }
+}
+
+#[cfg(feature = "gecko_profiler")]
+impl<'a> Drop for AutoProfilerLabel<'a> {
+    #[inline]
+    fn drop(&mut self) {
+        unsafe {
+            structs::Gecko_Destroy_AutoProfilerLabel(self.0);
+        }
+    }
+}
+
+/// Whether the Gecko profiler is currently active.
+///
+/// This implementation must be kept in sync with
+/// `mozilla::profiler::detail::RacyFeatures::IsActive`.
+#[cfg(feature = "gecko_profiler")]
+#[inline]
+pub fn profiler_is_active() -> bool {
+    use self::structs::profiler::detail;
+    use std::mem;
+    use std::sync::atomic::{AtomicU32, Ordering};
+
+    let active_and_features: &AtomicU32 = unsafe {
+        mem::transmute(&detail::RacyFeatures_sActiveAndFeatures)
+    };
+    (active_and_features.load(Ordering::Relaxed) & detail::RacyFeatures_Active) != 0
+}
+
+/// Always false when the Gecko profiler is disabled.
+#[cfg(not(feature = "gecko_profiler"))]
+#[inline]
+pub fn profiler_is_active() -> bool {
+    false
+}