/* 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 http://mozilla.org/MPL/2.0/. */
#![allow(unsafe_code)]
//! The rule tree.
use applicable_declarations::ApplicableDeclarationList;
#[cfg(feature = "gecko")]
use gecko::selector_parser::PseudoElement;
#[cfg(feature = "gecko")]
use malloc_size_of::{MallocSizeOf, MallocSizeOfOps};
use properties::{Importance, LonghandIdSet, PropertyDeclarationBlock};
use servo_arc::{Arc, ArcBorrow, NonZeroPtrMut};
use shared_lock::{Locked, StylesheetGuards, SharedRwLockReadGuard};
use smallvec::SmallVec;
use std::io::{self, Write};
use std::mem;
use std::ptr;
use std::sync::atomic::{AtomicPtr, AtomicUsize, Ordering};
use stylesheets::StyleRule;
use thread_state;
/// The rule tree, the structure servo uses to preserve the results of selector
/// matching.
///
/// This is organized as a tree of rules. When a node matches a set of rules,
/// they're inserted in order in the tree, starting with the less specific one.
///
/// When a rule is inserted in the tree, other elements may share the path up to
/// a given rule. If that's the case, we don't duplicate child nodes, but share
/// them.
///
/// When the rule node refcount drops to zero, it doesn't get freed. It gets
/// instead put into a free list, and it is potentially GC'd after a while in a
/// single-threaded fashion.
///
/// That way, a rule node that represents a likely-to-match-again rule (like a
/// :hover rule) can be reused if we haven't GC'd it yet.
///
/// See the discussion at https://github.com/servo/servo/pull/15562 and the IRC
/// logs at http://logs.glob.uno/?c=mozilla%23servo&s=3+Apr+2017&e=3+Apr+2017
/// logs from http://logs.glob.uno/?c=mozilla%23servo&s=3+Apr+2017&e=3+Apr+2017#c644094
/// to se a discussion about the different memory orderings used here.
#[derive(Debug)]
#[cfg_attr(feature = "servo", derive(MallocSizeOf))]
pub struct RuleTree {
root: StrongRuleNode,
}
impl Drop for RuleTree {
fn drop(&mut self) {
// GC the rule tree.
unsafe { self.gc(); }
// After the GC, the free list should be empty.
debug_assert_eq!(self.root.get().next_free.load(Ordering::Relaxed), FREE_LIST_SENTINEL);
// Remove the sentinel. This indicates that GCs will no longer occur.
// Any further drops of StrongRuleNodes must occur on the main thread,
// and will trigger synchronous dropping of the Rule nodes.
self.root.get().next_free.store(ptr::null_mut(), Ordering::Relaxed);
}
}
#[cfg(feature = "gecko")]
impl MallocSizeOf for RuleTree {
fn size_of(&self, ops: &mut MallocSizeOfOps) -> usize {
let mut n = unsafe { ops.malloc_size_of(self.root.ptr()) };
n += self.root.get().size_of(ops);
n
}
}
/// A style source for the rule node. It can either be a CSS style rule or a
/// declaration block.
///
/// Note that, even though the declaration block from inside the style rule
/// could be enough to implement the rule tree, keeping the whole rule provides
/// more debuggability, and also the ability of show those selectors to
/// devtools.
#[derive(Clone, Debug)]
pub enum StyleSource {
/// A style rule stable pointer.
Style(Arc<Locked<StyleRule>>),
/// A declaration block stable pointer.
Declarations(Arc<Locked<PropertyDeclarationBlock>>),
/// Indicates no style source. Used to save an Option wrapper around the stylesource in
/// RuleNode
None,
}
impl PartialEq for StyleSource {
fn eq(&self, other: &Self) -> bool {
self.ptr_equals(other)
}
}
impl StyleSource {
#[inline]
fn ptr_equals(&self, other: &Self) -> bool {
use self::StyleSource::*;
match (self, other) {
(&Style(ref one), &Style(ref other)) => Arc::ptr_eq(one, other),
(&Declarations(ref one), &Declarations(ref other)) => Arc::ptr_eq(one, other),
(&None, _) | (_, &None) => panic!("Should not check for equality between null StyleSource objects"),
_ => false,
}
}
fn dump<W: Write>(&self, guard: &SharedRwLockReadGuard, writer: &mut W) {
use self::StyleSource::*;
if let Style(ref rule) = *self {
let rule = rule.read_with(guard);
let _ = write!(writer, "{:?}", rule.selectors);
}
let _ = write!(writer, " -> {:?}", self.read(guard).declarations());
}
/// Read the style source guard, and obtain thus read access to the
/// underlying property declaration block.
#[inline]
pub fn read<'a>(&'a self, guard: &'a SharedRwLockReadGuard) -> &'a PropertyDeclarationBlock {
let block = match *self {
StyleSource::Style(ref rule) => &rule.read_with(guard).block,
StyleSource::Declarations(ref block) => block,
StyleSource::None => panic!("Cannot call read on StyleSource::None"),
};
block.read_with(guard)
}
/// Indicates if this StyleSource has a value
pub fn is_some(&self) -> bool {
match *self {
StyleSource::None => false,
_ => true,
}
}
}
/// This value exists here so a node that pushes itself to the list can know
/// that is in the free list by looking at is next pointer, and comparing it
/// with null.
///
/// The root node doesn't have a null pointer in the free list, but this value.
const FREE_LIST_SENTINEL: *mut RuleNode = 0x01 as *mut RuleNode;
/// A second sentinel value for the free list, indicating that it's locked (i.e.
/// another thread is currently adding an entry). We spin if we find this value.
const FREE_LIST_LOCKED: *mut RuleNode = 0x02 as *mut RuleNode;
impl RuleTree {
/// Construct a new rule tree.
pub fn new() -> Self {
RuleTree {
root: StrongRuleNode::new(Box::new(RuleNode::root())),
}
}
/// Get the root rule node.
pub fn root(&self) -> &StrongRuleNode {
&self.root
}
fn dump<W: Write>(&self, guards: &StylesheetGuards, writer: &mut W) {
let _ = writeln!(writer, " + RuleTree");
self.root.get().dump(guards, writer, 0);
}
/// Dump the rule tree to stdout.
pub fn dump_stdout(&self, guards: &StylesheetGuards) {
let mut stdout = io::stdout();
self.dump(guards, &mut stdout);
}
/// Inserts the given rules, that must be in proper order by specifity, and
/// returns the corresponding rule node representing the last inserted one.
///
/// !important rules are detected and inserted into the appropriate position
/// in the rule tree. This allows selector matching to ignore importance,
/// while still maintaining the appropriate cascade order in the rule tree.
pub fn insert_ordered_rules_with_important<'a, I>(
&self,
iter: I,
guards: &StylesheetGuards
) -> StrongRuleNode
where
I: Iterator<Item=(StyleSource, CascadeLevel)>,
{
use self::CascadeLevel::*;
let mut current = self.root.clone();
let mut last_level = current.get().level;
let mut found_important = false;
let mut important_style_attr = None;
let mut important_author = SmallVec::<[StyleSource; 4]>::new();
let mut important_user = SmallVec::<[StyleSource; 4]>::new();
let mut important_ua = SmallVec::<[StyleSource; 4]>::new();
let mut transition = None;
for (source, level) in iter {
debug_assert!(last_level <= level, "Not really ordered");
debug_assert!(!level.is_important(), "Important levels handled internally");
let any_important = {
let pdb = source.read(level.guard(guards));
pdb.any_important()
};
if any_important {
found_important = true;
match level {
AuthorNormal => important_author.push(source.clone()),
UANormal => important_ua.push(source.clone()),
UserNormal => important_user.push(source.clone()),
StyleAttributeNormal => {
debug_assert!(important_style_attr.is_none());
important_style_attr = Some(source.clone());
},
_ => {},
};
}
// We don't optimize out empty rules, even though we could.
//
// Inspector relies on every rule being inserted in the normal level
// at least once, in order to return the rules with the correct
// specificity order.
//
// TODO(emilio): If we want to apply these optimizations without
// breaking inspector's expectations, we'd need to run
// selector-matching again at the inspector's request. That may or
// may not be a better trade-off.
if matches!(level, Transitions) && found_important {
// There can be at most one transition, and it will come at
// the end of the iterator. Stash it and apply it after
// !important rules.
debug_assert!(transition.is_none());
transition = Some(source);
} else {
current = current.ensure_child(self.root.downgrade(), source, level);
}
last_level = level;
}
// Early-return in the common case of no !important declarations.
if !found_important {
return current;
}
//
// Insert important declarations, in order of increasing importance,
// followed by any transition rule.
//
for source in important_author.drain() {
current = current.ensure_child(self.root.downgrade(), source, AuthorImportant);
}
if let Some(source) = important_style_attr {
current = current.ensure_child(self.root.downgrade(), source, StyleAttributeImportant);
}
for source in important_user.drain() {
current = current.ensure_child(self.root.downgrade(), source, UserImportant);
}
for source in important_ua.drain() {
current = current.ensure_child(self.root.downgrade(), source, UAImportant);
}
if let Some(source) = transition {
current = current.ensure_child(self.root.downgrade(), source, Transitions);
}
current
}
/// Given a list of applicable declarations, insert the rules and return the
/// corresponding rule node.
pub fn compute_rule_node(
&self,
applicable_declarations: &mut ApplicableDeclarationList,
guards: &StylesheetGuards
) -> StrongRuleNode {
let rules = applicable_declarations.drain().map(|d| d.order_and_level());
let rule_node = self.insert_ordered_rules_with_important(rules, guards);
rule_node
}
/// Insert the given rules, that must be in proper order by specifity, and
/// return the corresponding rule node representing the last inserted one.
pub fn insert_ordered_rules<'a, I>(&self, iter: I) -> StrongRuleNode
where I: Iterator<Item=(StyleSource, CascadeLevel)>,
{
self.insert_ordered_rules_from(self.root.clone(), iter)
}
fn insert_ordered_rules_from<'a, I>(&self,
from: StrongRuleNode,
iter: I) -> StrongRuleNode
where I: Iterator<Item=(StyleSource, CascadeLevel)>,
{
let mut current = from;
let mut last_level = current.get().level;
for (source, level) in iter {
debug_assert!(last_level <= level, "Not really ordered");
current = current.ensure_child(self.root.downgrade(), source, level);
last_level = level;
}
current
}
/// This can only be called when no other threads is accessing this tree.
pub unsafe fn gc(&self) {
self.root.gc();
}
/// This can only be called when no other threads is accessing this tree.
pub unsafe fn maybe_gc(&self) {
self.root.maybe_gc();
}
/// Replaces a rule in a given level (if present) for another rule.
///
/// Returns the resulting node that represents the new path, or None if
/// the old path is still valid.
pub fn update_rule_at_level(&self,
level: CascadeLevel,
pdb: Option<ArcBorrow<Locked<PropertyDeclarationBlock>>>,
path: &StrongRuleNode,
guards: &StylesheetGuards,
important_rules_changed: &mut bool)
-> Option<StrongRuleNode> {
debug_assert!(level.is_unique_per_element());
// TODO(emilio): Being smarter with lifetimes we could avoid a bit of
// the refcount churn.
let mut current = path.clone();
*important_rules_changed = false;
// First walk up until the first less-or-equally specific rule.
let mut children = SmallVec::<[_; 10]>::new();
while current.get().level > level {
children.push((current.get().source.clone(), current.get().level));
current = current.parent().unwrap().clone();
}
// Then remove the one at the level we want to replace, if any.
//
// NOTE: Here we assume that only one rule can be at the level we're
// replacing.
//
// This is certainly true for HTML style attribute rules, animations and
// transitions, but could not be so for SMIL animations, which we'd need
// to special-case (isn't hard, it's just about removing the `if` and
// special cases, and replacing them for a `while` loop, avoiding the
// optimizations).
if current.get().level == level {
*important_rules_changed |= level.is_important();
if let Some(pdb) = pdb {
// If the only rule at the level we're replacing is exactly the
// same as `pdb`, we're done, and `path` is still valid.
//
// TODO(emilio): Another potential optimization is the one where
// we can just replace the rule at that level for `pdb`, and
// then we don't need to re-create the children, and `path` is
// also equally valid. This is less likely, and would require an
// in-place mutation of the source, which is, at best, fiddly,
// so let's skip it for now.
let is_here_already = match ¤t.get().source {
&StyleSource::Declarations(ref already_here) => {
pdb.with_arc(|arc| Arc::ptr_eq(arc, already_here))
},
_ => unreachable!("Replacing non-declarations style?"),
};
if is_here_already {
debug!("Picking the fast path in rule replacement");
return None;
}
}
current = current.parent().unwrap().clone();
}
debug_assert!(current.get().level != level,
"Multiple rules should've been replaced?");
// Insert the rule if it's relevant at this level in the cascade.
//
// These optimizations are likely to be important, because the levels
// where replacements apply (style and animations) tend to trigger
// pretty bad styling cases already.
if let Some(pdb) = pdb {
if level.is_important() {
if pdb.read_with(level.guard(guards)).any_important() {
current = current.ensure_child(self.root.downgrade(),
StyleSource::Declarations(pdb.clone_arc()),
level);
}
} else {
if pdb.read_with(level.guard(guards)).any_normal() {
current = current.ensure_child(self.root.downgrade(),
StyleSource::Declarations(pdb.clone_arc()),
level);
}
}
}
// Now the rule is in the relevant place, push the children as
// necessary.
let rule =
self.insert_ordered_rules_from(current, children.drain().rev());
Some(rule)
}
/// Returns new rule nodes without Transitions level rule.
pub fn remove_transition_rule_if_applicable(&self, path: &StrongRuleNode) -> StrongRuleNode {
// Return a clone if there is no transition level.
if path.cascade_level() != CascadeLevel::Transitions {
return path.clone();
}
path.parent().unwrap().clone()
}
/// Returns new rule node without rules from declarative animations.
pub fn remove_animation_rules(&self, path: &StrongRuleNode) -> StrongRuleNode {
// Return a clone if there are no animation rules.
if !path.has_animation_or_transition_rules() {
return path.clone();
}
let iter = path.self_and_ancestors().take_while(
|node| node.cascade_level() >= CascadeLevel::SMILOverride);
let mut last = path;
let mut children = SmallVec::<[_; 10]>::new();
for node in iter {
if !node.cascade_level().is_animation() {
children.push((node.get().source.clone(), node.cascade_level()));
}
last = node;
}
let rule = self.insert_ordered_rules_from(last.parent().unwrap().clone(), children.drain().rev());
rule
}
/// Returns new rule node by adding animation rules at transition level.
/// The additional rules must be appropriate for the transition
/// level of the cascade, which is the highest level of the cascade.
/// (This is the case for one current caller, the cover rule used
/// for CSS transitions.)
pub fn add_animation_rules_at_transition_level(
&self,
path: &StrongRuleNode,
pdb: Arc<Locked<PropertyDeclarationBlock>>,
guards: &StylesheetGuards,
) -> StrongRuleNode {
let mut dummy = false;
self.update_rule_at_level(CascadeLevel::Transitions,
Some(pdb.borrow_arc()),
path,
guards,
&mut dummy).expect("Should return a valid rule node")
}
}
/// The number of RuleNodes added to the free list before we will consider
/// doing a GC when calling maybe_gc(). (The value is copied from Gecko,
/// where it likely did not result from a rigorous performance analysis.)
const RULE_TREE_GC_INTERVAL: usize = 300;
/// The cascade level these rules are relevant at, as per[1][2][3].
///
/// Presentational hints for SVG and HTML are in the "author-level
/// zero-specificity" level, that is, right after user rules, and before author
/// rules.
///
/// The order of variants declared here is significant, and must be in
/// _ascending_ order of precedence.
///
/// [1]: https://drafts.csswg.org/css-cascade/#cascade-origin
/// [2]: https://drafts.csswg.org/css-cascade/#preshint
/// [3]: https://html.spec.whatwg.org/multipage/#presentational-hints
#[repr(u8)]
#[derive(Clone, Copy, Debug, Eq, PartialEq, PartialOrd)]
#[cfg_attr(feature = "servo", derive(MallocSizeOf))]
pub enum CascadeLevel {
/// Normal User-Agent rules.
UANormal = 0,
/// User normal rules.
UserNormal,
/// Presentational hints.
PresHints,
/// Author normal rules.
AuthorNormal,
/// Style attribute normal rules.
StyleAttributeNormal,
/// SVG SMIL animations.
SMILOverride,
/// CSS animations and script-generated animations.
Animations,
/// Author-supplied important rules.
AuthorImportant,
/// Style attribute important rules.
StyleAttributeImportant,
/// User important rules.
UserImportant,
/// User-agent important rules.
UAImportant,
/// Transitions
///
/// NB: If this changes from being last, change from_byte below.
Transitions,
}
impl CascadeLevel {
/// Converts a raw byte to a CascadeLevel.
pub unsafe fn from_byte(byte: u8) -> Self {
debug_assert!(byte <= CascadeLevel::Transitions as u8);
mem::transmute(byte)
}
/// Select a lock guard for this level
pub fn guard<'a>(&self, guards: &'a StylesheetGuards<'a>) -> &'a SharedRwLockReadGuard<'a> {
match *self {
CascadeLevel::UANormal |
CascadeLevel::UserNormal |
CascadeLevel::UserImportant |
CascadeLevel::UAImportant => guards.ua_or_user,
_ => guards.author,
}
}
/// Returns whether this cascade level is unique per element, in which case
/// we can replace the path in the cascade without fear.
pub fn is_unique_per_element(&self) -> bool {
match *self {
CascadeLevel::Transitions |
CascadeLevel::Animations |
CascadeLevel::SMILOverride |
CascadeLevel::StyleAttributeNormal |
CascadeLevel::StyleAttributeImportant => true,
_ => false,
}
}
/// Returns whether this cascade level represents important rules of some
/// sort.
#[inline]
pub fn is_important(&self) -> bool {
match *self {
CascadeLevel::AuthorImportant |
CascadeLevel::StyleAttributeImportant |
CascadeLevel::UserImportant |
CascadeLevel::UAImportant => true,
_ => false,
}
}
/// Returns the importance relevant for this rule. Pretty similar to
/// `is_important`.
#[inline]
pub fn importance(&self) -> Importance {
if self.is_important() {
Importance::Important
} else {
Importance::Normal
}
}
/// Returns whether this cascade level represents an animation rules.
#[inline]
pub fn is_animation(&self) -> bool {
match *self {
CascadeLevel::SMILOverride |
CascadeLevel::Animations |
CascadeLevel::Transitions => true,
_ => false,
}
}
}
// The root node never has siblings, but needs a free count. We use the same
// storage for both to save memory.
struct PrevSiblingOrFreeCount(AtomicPtr<RuleNode>);
impl PrevSiblingOrFreeCount {
fn new() -> Self {
PrevSiblingOrFreeCount(AtomicPtr::new(ptr::null_mut()))
}
unsafe fn as_prev_sibling(&self) -> &AtomicPtr<RuleNode> {
&self.0
}
unsafe fn as_free_count(&self) -> &AtomicUsize {
mem::transmute(&self.0)
}
}
/// A node in the rule tree.
pub struct RuleNode {
/// The root node. Only the root has no root pointer, for obvious reasons.
root: Option<WeakRuleNode>,
/// The parent rule node. Only the root has no parent.
parent: Option<StrongRuleNode>,
/// The actual style source, either coming from a selector in a StyleRule,
/// or a raw property declaration block (like the style attribute).
source: StyleSource,
/// The cascade level this rule is positioned at.
level: CascadeLevel,
refcount: AtomicUsize,
first_child: AtomicPtr<RuleNode>,
next_sibling: AtomicPtr<RuleNode>,
/// Previous sibling pointer for all non-root nodes.
///
/// For the root, stores the of RuleNodes we have added to the free list
/// since the last GC. (We don't update this if we rescue a RuleNode from
/// the free list. It's just used as a heuristic to decide when to run GC.)
prev_sibling_or_free_count: PrevSiblingOrFreeCount,
/// The next item in the rule tree free list, that starts on the root node.
///
/// When this is set to null, that means that the rule tree has been torn
/// down, and GCs will no longer occur. When this happens, StrongRuleNodes
/// may only be dropped on the main thread, and teardown happens
/// synchronously.
next_free: AtomicPtr<RuleNode>,
}
unsafe impl Sync for RuleTree {}
unsafe impl Send for RuleTree {}
// On Gecko builds, hook into the leak checking machinery.
#[cfg(feature = "gecko")]
#[cfg(debug_assertions)]
mod gecko_leak_checking {
use std::mem::size_of;
use std::os::raw::{c_char, c_void};
use super::RuleNode;
extern "C" {
pub fn NS_LogCtor(aPtr: *const c_void, aTypeName: *const c_char, aSize: u32);
pub fn NS_LogDtor(aPtr: *const c_void, aTypeName: *const c_char, aSize: u32);
}
static NAME: &'static [u8] = b"RuleNode\0";
/// Logs the creation of a heap-allocated object to Gecko's leak-checking machinery.
pub fn log_ctor(ptr: *const RuleNode) {
let s = NAME as *const [u8] as *const u8 as *const c_char;
unsafe {
NS_LogCtor(ptr as *const c_void, s, size_of::<RuleNode>() as u32);
}
}
/// Logs the destruction of a heap-allocated object to Gecko's leak-checking machinery.
pub fn log_dtor(ptr: *const RuleNode) {
let s = NAME as *const [u8] as *const u8 as *const c_char;
unsafe {
NS_LogDtor(ptr as *const c_void, s, size_of::<RuleNode>() as u32);
}
}
}
#[inline(always)]
fn log_new(_ptr: *const RuleNode) {
#[cfg(feature = "gecko")]
#[cfg(debug_assertions)]
gecko_leak_checking::log_ctor(_ptr);
}
#[inline(always)]
fn log_drop(_ptr: *const RuleNode) {
#[cfg(feature = "gecko")]
#[cfg(debug_assertions)]
gecko_leak_checking::log_dtor(_ptr);
}
impl RuleNode {
fn new(root: WeakRuleNode,
parent: StrongRuleNode,
source: StyleSource,
level: CascadeLevel) -> Self {
debug_assert!(root.upgrade().parent().is_none());
RuleNode {
root: Some(root),
parent: Some(parent),
source: source,
level: level,
refcount: AtomicUsize::new(1),
first_child: AtomicPtr::new(ptr::null_mut()),
next_sibling: AtomicPtr::new(ptr::null_mut()),
prev_sibling_or_free_count: PrevSiblingOrFreeCount::new(),
next_free: AtomicPtr::new(ptr::null_mut()),
}
}
fn root() -> Self {
RuleNode {
root: None,
parent: None,
source: StyleSource::None,
level: CascadeLevel::UANormal,
refcount: AtomicUsize::new(1),
first_child: AtomicPtr::new(ptr::null_mut()),
next_sibling: AtomicPtr::new(ptr::null_mut()),
prev_sibling_or_free_count: PrevSiblingOrFreeCount::new(),
next_free: AtomicPtr::new(FREE_LIST_SENTINEL),
}
}
fn is_root(&self) -> bool {
self.parent.is_none()
}
fn next_sibling(&self) -> Option<WeakRuleNode> {
// We use acquire semantics here to ensure proper synchronization while
// inserting in the child list.
let ptr = self.next_sibling.load(Ordering::Acquire);
if ptr.is_null() {
None
} else {
Some(WeakRuleNode::from_ptr(ptr))
}
}
fn prev_sibling(&self) -> &AtomicPtr<RuleNode> {
debug_assert!(!self.is_root());
unsafe { self.prev_sibling_or_free_count.as_prev_sibling() }
}
fn free_count(&self) -> &AtomicUsize {
debug_assert!(self.is_root());
unsafe { self.prev_sibling_or_free_count.as_free_count() }
}
/// Remove this rule node from the child list.
///
/// This method doesn't use proper synchronization, and it's expected to be
/// called in a single-threaded fashion, thus the unsafety.
///
/// This is expected to be called before freeing the node from the free
/// list.
unsafe fn remove_from_child_list(&self) {
debug!("Remove from child list: {:?}, parent: {:?}",
self as *const RuleNode, self.parent.as_ref().map(|p| p.ptr()));
// NB: The other siblings we use in this function can also be dead, so
// we can't use `get` here, since it asserts.
let prev_sibling =
self.prev_sibling().swap(ptr::null_mut(), Ordering::Relaxed);
let next_sibling =
self.next_sibling.swap(ptr::null_mut(), Ordering::Relaxed);
// Store the `next` pointer as appropriate, either in the previous
// sibling, or in the parent otherwise.
if prev_sibling.is_null() {
let parent = self.parent.as_ref().unwrap();
parent.get().first_child.store(next_sibling, Ordering::Relaxed);
} else {
let previous = &*prev_sibling;
previous.next_sibling.store(next_sibling, Ordering::Relaxed);
}
// Store the previous sibling pointer in the next sibling if present,
// otherwise we're done.
if !next_sibling.is_null() {
let next = &*next_sibling;
next.prev_sibling().store(prev_sibling, Ordering::Relaxed);
}
}
fn dump<W: Write>(&self, guards: &StylesheetGuards, writer: &mut W, indent: usize) {
const INDENT_INCREMENT: usize = 4;
for _ in 0..indent {
let _ = write!(writer, " ");
}
let _ = writeln!(writer, " - {:?} (ref: {:?}, parent: {:?})",
self as *const _, self.refcount.load(Ordering::Relaxed),
self.parent.as_ref().map(|p| p.ptr()));
for _ in 0..indent {
let _ = write!(writer, " ");
}
if self.source.is_some() {
self.source.dump(self.level.guard(guards), writer);
} else {
if indent != 0 {
warn!("How has this happened?");
}
let _ = write!(writer, "(root)");
}
let _ = write!(writer, "\n");
for child in self.iter_children() {
child.upgrade().get().dump(guards, writer, indent + INDENT_INCREMENT);
}
}
fn iter_children(&self) -> RuleChildrenListIter {
// See next_sibling to see why we need Acquire semantics here.
let first_child = self.first_child.load(Ordering::Acquire);
RuleChildrenListIter {
current: if first_child.is_null() {
None
} else {
Some(WeakRuleNode::from_ptr(first_child))
}
}
}
}
#[cfg(feature = "gecko")]
impl MallocSizeOf for RuleNode {
fn size_of(&self, ops: &mut MallocSizeOfOps) -> usize {
let mut n = 0;
for child in self.iter_children() {
n += unsafe { ops.malloc_size_of(child.ptr()) };
n += unsafe { (*child.ptr()).size_of(ops) };
}
n
}
}
// FIXME: use std::ptr::NonNull when Firefox requires Rust 1.25+
#[derive(Clone)]
struct WeakRuleNode {
p: NonZeroPtrMut<RuleNode>,
}
/// A strong reference to a rule node.
#[derive(Debug, Eq, Hash, PartialEq)]
pub struct StrongRuleNode {
p: NonZeroPtrMut<RuleNode>,
}
#[cfg(feature = "servo")]
malloc_size_of_is_0!(StrongRuleNode);
impl StrongRuleNode {
fn new(n: Box<RuleNode>) -> Self {
debug_assert_eq!(n.parent.is_none(), !n.source.is_some());
let ptr = Box::into_raw(n);
log_new(ptr);
debug!("Creating rule node: {:p}", ptr);
StrongRuleNode::from_ptr(ptr)
}
fn from_ptr(ptr: *mut RuleNode) -> Self {
StrongRuleNode {
p: NonZeroPtrMut::new(ptr)
}
}
fn downgrade(&self) -> WeakRuleNode {
WeakRuleNode::from_ptr(self.ptr())
}
/// Get the parent rule node of this rule node.
pub fn parent(&self) -> Option<&StrongRuleNode> {
self.get().parent.as_ref()
}
fn ensure_child(
&self,
root: WeakRuleNode,
source: StyleSource,
level: CascadeLevel
) -> StrongRuleNode {
let mut last = None;
// NB: This is an iterator over _weak_ nodes.
//
// It's fine though, because nothing can make us GC while this happens,
// and this happens to be hot.
//
// TODO(emilio): We could actually make this even less hot returning a
// WeakRuleNode, and implementing this on WeakRuleNode itself...
for child in self.get().iter_children() {
let child_node = unsafe { &*child.ptr() };
if child_node.level == level &&
child_node.source.ptr_equals(&source) {
return child.upgrade();
}
last = Some(child);
}
let mut node = Box::new(RuleNode::new(root,
self.clone(),
source.clone(),
level));
let new_ptr: *mut RuleNode = &mut *node;
loop {
let next;
{
let last_node = last.as_ref().map(|l| unsafe { &*l.ptr() });
let next_sibling_ptr = match last_node {
Some(ref l) => &l.next_sibling,
None => &self.get().first_child,
};
// We use `AqcRel` semantics to ensure the initializing writes
// in `node` are visible after the swap succeeds.
let existing =
next_sibling_ptr.compare_and_swap(ptr::null_mut(),
new_ptr,
Ordering::AcqRel);
if existing.is_null() {
// Now we know we're in the correct position in the child
// list, we can set the back pointer, knowing that this will
// only be accessed again in a single-threaded manner when
// we're sweeping possibly dead nodes.
if let Some(ref l) = last {
node.prev_sibling().store(l.ptr(), Ordering::Relaxed);
}
return StrongRuleNode::new(node);
}
// Existing is not null: some thread inserted a child node since
// we accessed `last`.
next = WeakRuleNode::from_ptr(existing);
if unsafe { &*next.ptr() }.source.ptr_equals(&source) {
// That node happens to be for the same style source, use
// that, and let node fall out of scope.
return next.upgrade();
}
}
// Try again inserting after the new last child.
last = Some(next);
}
}
/// Raw pointer to the RuleNode
pub fn ptr(&self) -> *mut RuleNode {
self.p.ptr()
}
fn get(&self) -> &RuleNode {
if cfg!(debug_assertions) {
let node = unsafe { &*self.ptr() };
assert!(node.refcount.load(Ordering::Relaxed) > 0);
}
unsafe { &*self.ptr() }
}
/// Get the style source corresponding to this rule node. May return `None`
/// if it's the root node, which means that the node hasn't matched any
/// rules.
pub fn style_source(&self) -> &StyleSource {
&self.get().source
}
/// The cascade level for this node
pub fn cascade_level(&self) -> CascadeLevel {
self.get().level
}
/// Get the importance that this rule node represents.
pub fn importance(&self) -> Importance {
self.get().level.importance()
}
/// Get an iterator for this rule node and its ancestors.
pub fn self_and_ancestors(&self) -> SelfAndAncestors {
SelfAndAncestors {
current: Some(self)
}
}
/// Returns whether this node has any child, only intended for testing
/// purposes, and called on a single-threaded fashion only.
pub unsafe fn has_children_for_testing(&self) -> bool {
!self.get().first_child.load(Ordering::Relaxed).is_null()
}
unsafe fn pop_from_free_list(&self) -> Option<WeakRuleNode> {
// NB: This can run from the root node destructor, so we can't use
// `get()`, since it asserts the refcount is bigger than zero.
let me = &*self.ptr();
debug_assert!(me.is_root());
// FIXME(#14213): Apparently the layout data can be gone from script.
//
// That's... suspicious, but it's fine if it happens for the rule tree
// case, so just don't crash in the case we're doing the final GC in
// script.
debug_assert!(!thread_state::get().is_worker() &&
(thread_state::get().is_layout() ||
thread_state::get().is_script()));
let current = me.next_free.load(Ordering::Relaxed);
if current == FREE_LIST_SENTINEL {
return None;
}
debug_assert!(!current.is_null(),
"Multiple threads are operating on the free list at the \
same time?");
debug_assert!(current != self.ptr(),
"How did the root end up in the free list?");
let next = (*current).next_free.swap(ptr::null_mut(), Ordering::Relaxed);
debug_assert!(!next.is_null(),
"How did a null pointer end up in the free list?");
me.next_free.store(next, Ordering::Relaxed);
debug!("Popping from free list: cur: {:?}, next: {:?}", current, next);
Some(WeakRuleNode::from_ptr(current))
}
unsafe fn assert_free_list_has_no_duplicates_or_null(&self) {
assert!(cfg!(debug_assertions), "This is an expensive check!");
use hash::FnvHashSet;
let me = &*self.ptr();
assert!(me.is_root());
let mut current = self.ptr();
let mut seen = FnvHashSet::default();
while current != FREE_LIST_SENTINEL {
let next = (*current).next_free.load(Ordering::Relaxed);
assert!(!next.is_null());
assert!(!seen.contains(&next));
seen.insert(next);
current = next;
}
}
unsafe fn gc(&self) {
if cfg!(debug_assertions) {
self.assert_free_list_has_no_duplicates_or_null();
}
// NB: This can run from the root node destructor, so we can't use
// `get()`, since it asserts the refcount is bigger than zero.
let me = &*self.ptr();
debug_assert!(me.is_root(), "Can't call GC on a non-root node!");
while let Some(weak) = self.pop_from_free_list() {
let node = &*weak.ptr();
if node.refcount.load(Ordering::Relaxed) != 0 {
// Nothing to do, the node is still alive.
continue;
}
debug!("GC'ing {:?}", weak.ptr());
node.remove_from_child_list();
log_drop(weak.ptr());
let _ = Box::from_raw(weak.ptr());
}
me.free_count().store(0, Ordering::Relaxed);
debug_assert_eq!(me.next_free.load(Ordering::Relaxed), FREE_LIST_SENTINEL);
}
unsafe fn maybe_gc(&self) {
debug_assert!(self.get().is_root(), "Can't call GC on a non-root node!");
if self.get().free_count().load(Ordering::Relaxed) > RULE_TREE_GC_INTERVAL {
self.gc();
}
}
/// Implementation of `nsRuleNode::HasAuthorSpecifiedRules` for Servo rule
/// nodes.
///
/// Returns true if any properties specified by `rule_type_mask` was set by
/// an author rule.
#[cfg(feature = "gecko")]
pub fn has_author_specified_rules<E>(
&self,
mut element: E,
mut pseudo: Option<PseudoElement>,
guards: &StylesheetGuards,
rule_type_mask: u32,
author_colors_allowed: bool,
) -> bool
where
E: ::dom::TElement
{
use gecko_bindings::structs::NS_AUTHOR_SPECIFIED_BACKGROUND;
use gecko_bindings::structs::NS_AUTHOR_SPECIFIED_BORDER;
use gecko_bindings::structs::NS_AUTHOR_SPECIFIED_PADDING;
use properties::{CSSWideKeyword, LonghandId, LonghandIdSet};
use properties::{PropertyDeclaration, PropertyDeclarationId};
use std::borrow::Cow;
use values::specified::Color;
// Reset properties:
const BACKGROUND_PROPS: &'static [LonghandId] = &[
LonghandId::BackgroundColor,
LonghandId::BackgroundImage,
];
const BORDER_PROPS: &'static [LonghandId] = &[
LonghandId::BorderTopColor,
LonghandId::BorderTopStyle,
LonghandId::BorderTopWidth,
LonghandId::BorderRightColor,
LonghandId::BorderRightStyle,
LonghandId::BorderRightWidth,
LonghandId::BorderBottomColor,
LonghandId::BorderBottomStyle,
LonghandId::BorderBottomWidth,
LonghandId::BorderLeftColor,
LonghandId::BorderLeftStyle,
LonghandId::BorderLeftWidth,
LonghandId::BorderTopLeftRadius,
LonghandId::BorderTopRightRadius,
LonghandId::BorderBottomRightRadius,
LonghandId::BorderBottomLeftRadius,
LonghandId::BorderInlineStartColor,
LonghandId::BorderInlineStartStyle,
LonghandId::BorderInlineStartWidth,
LonghandId::BorderInlineEndColor,
LonghandId::BorderInlineEndStyle,
LonghandId::BorderInlineEndWidth,
LonghandId::BorderBlockStartColor,
LonghandId::BorderBlockStartStyle,
LonghandId::BorderBlockStartWidth,
LonghandId::BorderBlockEndColor,
LonghandId::BorderBlockEndStyle,
LonghandId::BorderBlockEndWidth,
];
const PADDING_PROPS: &'static [LonghandId] = &[
LonghandId::PaddingTop,
LonghandId::PaddingRight,
LonghandId::PaddingBottom,
LonghandId::PaddingLeft,
LonghandId::PaddingInlineStart,
LonghandId::PaddingInlineEnd,
LonghandId::PaddingBlockStart,
LonghandId::PaddingBlockEnd,
];
// Set of properties that we are currently interested in.
let mut properties = LonghandIdSet::new();
if rule_type_mask & NS_AUTHOR_SPECIFIED_BACKGROUND != 0 {
for id in BACKGROUND_PROPS {
properties.insert(*id);
}
}
if rule_type_mask & NS_AUTHOR_SPECIFIED_BORDER != 0 {
for id in BORDER_PROPS {
properties.insert(*id);
}
}
if rule_type_mask & NS_AUTHOR_SPECIFIED_PADDING != 0 {
for id in PADDING_PROPS {
properties.insert(*id);
}
}
// If author colors are not allowed, only claim to have author-specified
// rules if we're looking at a non-color property or if we're looking at
// the background color and it's set to transparent.
const IGNORED_WHEN_COLORS_DISABLED: &'static [LonghandId] = &[
LonghandId::BackgroundImage,
LonghandId::BorderTopColor,
LonghandId::BorderRightColor,
LonghandId::BorderBottomColor,
LonghandId::BorderLeftColor,
LonghandId::BorderInlineStartColor,
LonghandId::BorderInlineEndColor,
LonghandId::BorderBlockStartColor,
LonghandId::BorderBlockEndColor,
];
if !author_colors_allowed {
for id in IGNORED_WHEN_COLORS_DISABLED {
properties.remove(*id);
}
}
let mut element_rule_node = Cow::Borrowed(self);
loop {
// We need to be careful not to count styles covered up by
// user-important or UA-important declarations. But we do want to
// catch explicit inherit styling in those and check our parent
// element to see whether we have user styling for those properties.
// Note that we don't care here about inheritance due to lack of a
// specified value, since all the properties we care about are reset
// properties.
let mut inherited_properties = LonghandIdSet::new();
let mut have_explicit_ua_inherit = false;
for node in element_rule_node.self_and_ancestors() {
let source = node.style_source();
let declarations = if source.is_some() {
source.read(node.cascade_level().guard(guards)).declaration_importance_iter()
} else {
continue
};
// Iterate over declarations of the longhands we care about.
let node_importance = node.importance();
let longhands = declarations.rev()
.filter_map(|(declaration, importance)| {
if importance != node_importance { return None }
match declaration.id() {
PropertyDeclarationId::Longhand(id) => {
Some((id, declaration))
}
_ => None
}
});
match node.cascade_level() {
// Non-author rules:
CascadeLevel::UANormal |
CascadeLevel::UAImportant |
CascadeLevel::UserNormal |
CascadeLevel::UserImportant => {
for (id, declaration) in longhands {
if properties.contains(id) {
// This property was set by a non-author rule.
// Stop looking for it in this element's rule
// nodes.
properties.remove(id);
// However, if it is inherited, then it might be
// inherited from an author rule from an
// ancestor element's rule nodes.
if declaration.get_css_wide_keyword() == Some(CSSWideKeyword::Inherit) {
have_explicit_ua_inherit = true;
inherited_properties.insert(id);
}
}
}
}
// Author rules:
CascadeLevel::PresHints |
CascadeLevel::AuthorNormal |
CascadeLevel::StyleAttributeNormal |
CascadeLevel::SMILOverride |
CascadeLevel::Animations |
CascadeLevel::AuthorImportant |
CascadeLevel::StyleAttributeImportant |
CascadeLevel::Transitions => {
for (id, declaration) in longhands {
if properties.contains(id) {
if !author_colors_allowed {
if let PropertyDeclaration::BackgroundColor(ref color) = *declaration {
return *color == Color::transparent()
}
}
return true
}
}
}
}
}
if !have_explicit_ua_inherit { break }
// Continue to the parent element and search for the inherited properties.
if let Some(pseudo) = pseudo.take() {
if pseudo.inherits_from_default_values() {
break;
}
} else {
element = match element.inheritance_parent() {
Some(parent) => parent,
None => break
};
let parent_data = element.mutate_data().unwrap();
let parent_rule_node = parent_data.styles.primary().rules().clone();
element_rule_node = Cow::Owned(parent_rule_node);
}
properties = inherited_properties;
}
false
}
/// Returns true if there is either animation or transition level rule.
pub fn has_animation_or_transition_rules(&self) -> bool {
self.self_and_ancestors()
.take_while(|node| node.cascade_level() >= CascadeLevel::SMILOverride)
.any(|node| node.cascade_level().is_animation())
}
/// Get a set of properties whose CascadeLevel are higher than Animations
/// but not equal to Transitions.
///
/// If there are any custom properties, we set the boolean value of the
/// returned tuple to true.
pub fn get_properties_overriding_animations(&self,
guards: &StylesheetGuards)
-> (LonghandIdSet, bool) {
use properties::PropertyDeclarationId;
// We want to iterate over cascade levels that override the animations
// level, i.e. !important levels and the transitions level.
//
// However, we actually want to skip the transitions level because
// although it is higher in the cascade than animations, when both
// transitions and animations are present for a given element and
// property, transitions are suppressed so that they don't actually
// override animations.
let iter =
self.self_and_ancestors()
.skip_while(|node| node.cascade_level() == CascadeLevel::Transitions)
.take_while(|node| node.cascade_level() > CascadeLevel::Animations);
let mut result = (LonghandIdSet::new(), false);
for node in iter {
let style = node.style_source();
for (decl, important) in style.read(node.cascade_level().guard(guards))
.declaration_importance_iter() {
// Although we are only iterating over cascade levels that
// override animations, in a given property declaration block we
// can have a mixture of !important and non-!important
// declarations but only the !important declarations actually
// override animations.
if important.important() {
match decl.id() {
PropertyDeclarationId::Longhand(id) => result.0.insert(id),
PropertyDeclarationId::Custom(_) => result.1 = true
}
}
}
}
result
}
/// Returns PropertyDeclarationBlock for this node.
/// This function must be called only for animation level node.
fn get_animation_style(&self) -> &Arc<Locked<PropertyDeclarationBlock>> {
debug_assert!(self.cascade_level().is_animation(),
"The cascade level should be an animation level");
match *self.style_source() {
StyleSource::Declarations(ref block) => block,
StyleSource::Style(_) => unreachable!("animating style should not be a style rule"),
StyleSource::None => unreachable!("animating style should not be none"),
}
}
/// Returns SMIL override declaration block if exists.
pub fn get_smil_animation_rule(&self) -> Option<&Arc<Locked<PropertyDeclarationBlock>>> {
if cfg!(feature = "servo") {
// Servo has no knowledge of a SMIL rule, so just avoid looking for it.
return None;
}
self.self_and_ancestors()
.take_while(|node| node.cascade_level() >= CascadeLevel::SMILOverride)
.find(|node| node.cascade_level() == CascadeLevel::SMILOverride)
.map(|node| node.get_animation_style())
}
}
/// An iterator over a rule node and its ancestors.
#[derive(Clone)]
pub struct SelfAndAncestors<'a> {
current: Option<&'a StrongRuleNode>,
}
impl<'a> Iterator for SelfAndAncestors<'a> {
type Item = &'a StrongRuleNode;
fn next(&mut self) -> Option<Self::Item> {
self.current.map(|node| {
self.current = node.parent();
node
})
}
}
impl Clone for StrongRuleNode {
fn clone(&self) -> Self {
debug!("{:?}: {:?}+", self.ptr(), self.get().refcount.load(Ordering::Relaxed));
debug_assert!(self.get().refcount.load(Ordering::Relaxed) > 0);
self.get().refcount.fetch_add(1, Ordering::Relaxed);
StrongRuleNode::from_ptr(self.ptr())
}
}
impl Drop for StrongRuleNode {
fn drop(&mut self) {
let node = unsafe { &*self.ptr() };
debug!("{:?}: {:?}-", self.ptr(), node.refcount.load(Ordering::Relaxed));
debug!("Dropping node: {:?}, root: {:?}, parent: {:?}",
self.ptr(),
node.root.as_ref().map(|r| r.ptr()),
node.parent.as_ref().map(|p| p.ptr()));
let should_drop = {
debug_assert!(node.refcount.load(Ordering::Relaxed) > 0);
node.refcount.fetch_sub(1, Ordering::Relaxed) == 1
};
if !should_drop {
return
}
debug_assert_eq!(node.first_child.load(Ordering::Acquire),
ptr::null_mut());
if node.parent.is_none() {
debug!("Dropping root node!");
// The free list should be null by this point
debug_assert!(node.next_free.load(Ordering::Relaxed).is_null());
log_drop(self.ptr());
let _ = unsafe { Box::from_raw(self.ptr()) };
return;
}
let root = unsafe { &*node.root.as_ref().unwrap().ptr() };
let free_list = &root.next_free;
let mut old_head = free_list.load(Ordering::Relaxed);
// If the free list is null, that means that the rule tree has been
// formally torn down, and the last standard GC has already occurred.
// We require that any callers using the rule tree at this point are
// on the main thread only, which lets us trigger a synchronous GC
// here to avoid leaking anything. We use the GC machinery, rather
// than just dropping directly, so that we benefit from the iterative
// destruction and don't trigger unbounded recursion during drop. See
// [1] and the associated crashtest.
//
// [1] https://bugzilla.mozilla.org/show_bug.cgi?id=439184
if old_head.is_null() {
debug_assert!(!thread_state::get().is_worker() &&
(thread_state::get().is_layout() ||
thread_state::get().is_script()));
// Add the node as the sole entry in the free list.
debug_assert!(node.next_free.load(Ordering::Relaxed).is_null());
node.next_free.store(FREE_LIST_SENTINEL, Ordering::Relaxed);
free_list.store(node as *const _ as *mut _, Ordering::Relaxed);
// Invoke the GC.
//
// Note that we need hold a strong reference to the root so that it
// doesn't go away during the GC (which would happen if we're freeing
// the last external reference into the rule tree). This is nicely
// enforced by having the gc() method live on StrongRuleNode rather than
// RuleNode.
let strong_root: StrongRuleNode = node.root.as_ref().unwrap().upgrade();
unsafe { strong_root.gc(); }
// Leave the free list null, like we found it, such that additional
// drops for straggling rule nodes will take this same codepath.
debug_assert_eq!(root.next_free.load(Ordering::Relaxed),
FREE_LIST_SENTINEL);
root.next_free.store(ptr::null_mut(), Ordering::Relaxed);
// Return. If strong_root is the last strong reference to the root,
// this re-enter StrongRuleNode::drop, and take the root-dropping
// path earlier in this function.
return;
}
// We're sure we're already in the free list, don't spinloop if we're.
// Note that this is just a fast path, so it doesn't need to have an
// strong memory ordering.
if node.next_free.load(Ordering::Relaxed) != ptr::null_mut() {
return;
}
// Ensure we "lock" the free list head swapping it with FREE_LIST_LOCKED.
//
// Note that we use Acquire/Release semantics for the free list
// synchronization, in order to guarantee that the next_free
// reads/writes we do below are properly visible from multiple threads
// racing.
loop {
match free_list.compare_exchange_weak(old_head,
FREE_LIST_LOCKED,
Ordering::Acquire,
Ordering::Relaxed) {
Ok(..) => {
if old_head != FREE_LIST_LOCKED {
break;
}
},
Err(new) => old_head = new,
}
}
// If other thread has raced with use while using the same rule node,
// just store the old head again, we're done.
//
// Note that we can use relaxed operations for loading since we're
// effectively locking the free list with Acquire/Release semantics, and
// the memory ordering is already guaranteed by that locking/unlocking.
if node.next_free.load(Ordering::Relaxed) != ptr::null_mut() {
free_list.store(old_head, Ordering::Release);
return;
}
// Else store the old head as the next pointer, and store ourselves as
// the new head of the free list.
//
// This can be relaxed since this pointer won't be read until GC.
node.next_free.store(old_head, Ordering::Relaxed);
// Increment the free count. This doesn't need to be an RMU atomic
// operation, because the free list is "locked".
let old_free_count = root.free_count().load(Ordering::Relaxed);
root.free_count().store(old_free_count + 1, Ordering::Relaxed);
// This can be release because of the locking of the free list, that
// ensures that all the other nodes racing with this one are using
// `Acquire`.
free_list.store(self.ptr(), Ordering::Release);
}
}
impl<'a> From<&'a StrongRuleNode> for WeakRuleNode {
fn from(node: &'a StrongRuleNode) -> Self {
WeakRuleNode::from_ptr(node.ptr())
}
}
impl WeakRuleNode {
fn upgrade(&self) -> StrongRuleNode {
debug!("Upgrading weak node: {:p}", self.ptr());
let node = unsafe { &*self.ptr() };
node.refcount.fetch_add(1, Ordering::Relaxed);
StrongRuleNode::from_ptr(self.ptr())
}
fn from_ptr(ptr: *mut RuleNode) -> Self {
WeakRuleNode {
p: NonZeroPtrMut::new(ptr)
}
}
fn ptr(&self) -> *mut RuleNode {
self.p.ptr()
}
}
struct RuleChildrenListIter {
current: Option<WeakRuleNode>,
}
impl Iterator for RuleChildrenListIter {
type Item = WeakRuleNode;
fn next(&mut self) -> Option<Self::Item> {
self.current.take().map(|current| {
self.current = unsafe { &*current.ptr() }.next_sibling();
current
})
}
}