servo: Merge #17701 - reuse the bloom filter and style sharing cache …

…across traversals (from bholley:reuse_allocations); r=emilio

https://bugzilla.mozilla.org/show_bug.cgi?id=1380198

Source-Repo: https://github.com/servo/servo
Source-Revision: ebfc8f585834948f9b7564ffe382a6e266edf738

servo/components/layout/Cargo.toml

@@ -26,7 +26,7 @@ log = "0.3.5"
 msg = {path = "../msg"}
 net_traits = {path = "../net_traits"}
 ordered-float = "0.4"
-parking_lot = "0.3.3"
+parking_lot = "0.4"
 profile_traits = {path = "../profile_traits"}
 range = {path = "../range"}
 rayon = "0.8"

servo/components/layout_thread/Cargo.toml

@@ -23,7 +23,7 @@ lazy_static = "0.2"
 log = "0.3.5"
 msg = {path = "../msg"}
 net_traits = {path = "../net_traits"}
-parking_lot = {version = "0.3.3", features = ["nightly"]}
+parking_lot = {version = "0.4", features = ["nightly"]}
 profile_traits = {path = "../profile_traits"}
 rayon = "0.8"
 script = {path = "../script"}

servo/components/script/Cargo.toml

@@ -65,7 +65,7 @@ net_traits = {path = "../net_traits"}
 num-traits = "0.1.32"
 offscreen_gl_context = { version = "0.11", features = ["serde"] }
 open = "1.1.1"
-parking_lot = "0.3"
+parking_lot = "0.4"
 phf = "0.7.18"
 profile_traits = {path = "../profile_traits"}
 range = {path = "../range"}

servo/components/servo_arc/Cargo.toml

@@ -14,5 +14,6 @@ servo = ["serde", "heapsize"]
 
 [dependencies]
 heapsize = {version = "0.4.0", optional = true}
-serde = {version = "1.0", optional = true}
 nodrop = {version = "0.1.8"}
+serde = {version = "1.0", optional = true}
+stable_deref_trait = "1.0.0"

servo/components/servo_arc/lib.rs

@@ -22,14 +22,16 @@
 // duplicate those here.
 #![allow(missing_docs)]
 
-#[cfg(feature = "servo")] extern crate serde;
 extern crate nodrop;
+#[cfg(feature = "servo")] extern crate serde;
+extern crate stable_deref_trait;
 
 #[cfg(feature = "servo")]
 use heapsize::HeapSizeOf;
 use nodrop::NoDrop;
 #[cfg(feature = "servo")]
 use serde::{Deserialize, Serialize};
+use stable_deref_trait::{CloneStableDeref, StableDeref};
 use std::{isize, usize};
 use std::borrow;
 use std::cmp::Ordering;
@@ -432,6 +434,9 @@ impl<T: ?Sized> AsRef<T> for Arc<T> {
     }
 }
 
+unsafe impl<T: ?Sized> StableDeref for Arc<T> {}
+unsafe impl<T: ?Sized> CloneStableDeref for Arc<T> {}
+
 // This is what the HeapSize crate does for regular arc, but is questionably
 // sound. See https://github.com/servo/heapsize/issues/37
 #[cfg(feature = "servo")]

servo/components/style/Cargo.toml

@@ -54,7 +54,8 @@ num_cpus = {version = "1.1.0", optional = true}
 num-integer = "0.1.32"
 num-traits = "0.1.32"
 ordered-float = "0.4"
-parking_lot = "0.3.3"
+owning_ref = "0.3.3"
+parking_lot = "0.4"
 pdqsort = "0.1.0"
 precomputed-hash = "0.1"
 rayon = "0.8"

servo/components/style/bloom.rs

@@ -7,9 +7,18 @@
 
 #![deny(missing_docs)]
 
+use atomic_refcell::{AtomicRefMut, AtomicRefCell};
 use dom::{SendElement, TElement};
+use owning_ref::OwningHandle;
 use selectors::bloom::BloomFilter;
 use smallvec::SmallVec;
+use stylearc::Arc;
+
+/// Bloom filters are large allocations, so we store them in thread-local storage
+/// such that they can be reused across style traversals. StyleBloom is responsible
+/// for ensuring that the bloom filter is zeroed when it is dropped.
+thread_local!(static BLOOM_KEY: Arc<AtomicRefCell<BloomFilter>> =
+              Arc::new(AtomicRefCell::new(BloomFilter::new())));
 
 /// A struct that allows us to fast-reject deep descendant selectors avoiding
 /// selector-matching.
@@ -43,8 +52,11 @@ use smallvec::SmallVec;
 ///    immutable during a restyle.
 ///
 pub struct StyleBloom<E: TElement> {
-    /// The bloom filter per se.
-    filter: Box<BloomFilter>,
+    /// A handle to the bloom filter from the thread upon which this StyleBloom
+    /// was created. We use AtomicRefCell so that this is all |Send|, which allows
+    /// StyleBloom to live in ThreadLocalStyleContext, which is dropped from the
+    /// parent thread.
+    filter: OwningHandle<Arc<AtomicRefCell<BloomFilter>>, AtomicRefMut<'static, BloomFilter>>,
 
     /// The stack of elements that this bloom filter contains, along with the
     /// number of hashes pushed for each element.
@@ -101,11 +113,23 @@ fn each_relevant_element_hash<E, F>(element: E, mut f: F)
     });
 }
 
+impl<E: TElement> Drop for StyleBloom<E> {
+    fn drop(&mut self) {
+        // Leave the reusable bloom filter in a zeroed state.
+        self.clear();
+    }
+}
+
 impl<E: TElement> StyleBloom<E> {
-    /// Create an empty `StyleBloom`.
+    /// Create an empty `StyleBloom`. Because StyleBloom acquires the thread-
+    /// local filter buffer, creating multiple live StyleBloom instances at
+    /// the same time on the same thread will panic.
     pub fn new() -> Self {
+        let bloom_arc = BLOOM_KEY.with(|b| b.clone());
+        let filter = OwningHandle::new_with_fn(bloom_arc, |x| unsafe { x.as_ref() }.unwrap().borrow_mut());
+        debug_assert!(filter.is_zeroed(), "Forgot to zero the bloom filter last time");
         StyleBloom {
-            filter: Box::new(BloomFilter::new()),
+            filter: filter,
             elements: Default::default(),
             pushed_hashes: Default::default(),
         }

servo/components/style/lib.rs

@@ -67,6 +67,7 @@ pub extern crate nsstring_vendor as nsstring;
 extern crate num_integer;
 extern crate num_traits;
 extern crate ordered_float;
+extern crate owning_ref;
 extern crate parking_lot;
 extern crate pdqsort;
 #[cfg(feature = "gecko")] extern crate precomputed_hash;