style: Add refcount logging to servo_arc.

Differential Revision: https://phabricator.services.mozilla.com/D32173

components/servo_arc/Cargo.toml

@@ -12,6 +12,7 @@ path = "lib.rs"
 
 [features]
 servo = ["serde"]
+gecko = []
 
 [dependencies]
 nodrop = {version = "0.1.8"}

components/servo_arc/lib.rs

@@ -42,7 +42,7 @@ use std::fmt;
 use std::hash::{Hash, Hasher};
 use std::iter::{ExactSizeIterator, Iterator};
 use std::marker::PhantomData;
-use std::mem;
+use std::mem::{self, align_of, size_of};
 use std::ops::{Deref, DerefMut};
 use std::os::raw::c_void;
 use std::process;
@@ -115,7 +115,10 @@ pub struct Arc<T: ?Sized> {
 /// Once the mutation is finished, you can call `.shareable()` and get a regular `Arc`
 /// out of it.
 ///
-/// ```rust
+/// Ignore the doctest below there's no way to skip building with refcount
+/// logging during doc tests (see rust-lang/rust#45599).
+///
+/// ```rust,ignore
 /// # use servo_arc::UniqueArc;
 /// let data = [1, 2, 3, 4, 5];
 /// let mut x = UniqueArc::new(data);
@@ -169,18 +172,35 @@ impl<T> Arc<T> {
     /// Construct an `Arc<T>`
     #[inline]
     pub fn new(data: T) -> Self {
-        let x = Box::new(ArcInner {
+        let ptr = Box::into_raw(Box::new(ArcInner {
             count: atomic::AtomicUsize::new(1),
             data,
-        });
+        }));
+
+        #[cfg(all(feature = "gecko", debug_assertions))]
+        unsafe {
+            // FIXME(emilio): Would be so amazing to have
+            // std::intrinsics::type_name() around, so that we could also report
+            // a real size.
+            NS_LogCtor(ptr as *const _, b"ServoArc\0".as_ptr() as *const _, 8);
+        }
+
         unsafe {
             Arc {
-                p: ptr::NonNull::new_unchecked(Box::into_raw(x)),
+                p: ptr::NonNull::new_unchecked(ptr),
                 phantom: PhantomData,
             }
         }
     }
 
+    /// Construct an intentionally-leaked arc.
+    #[inline]
+    pub fn new_leaked(data: T) -> Self {
+        let arc = Self::new(data);
+        arc.mark_as_intentionally_leaked();
+        arc
+    }
+
     /// Convert the Arc<T> to a raw pointer, suitable for use across FFI
     ///
     /// Note: This returns a pointer to the data T, which is offset in the allocation.
@@ -290,9 +310,29 @@ impl<T: ?Sized> Arc<T> {
         unsafe { &*self.ptr() }
     }
 
-    // Non-inlined part of `drop`. Just invokes the destructor.
+    #[inline(always)]
+    fn record_drop(&self) {
+        #[cfg(all(feature = "gecko", debug_assertions))]
+        unsafe {
+            NS_LogDtor(self.ptr() as *const _, b"ServoArc\0".as_ptr() as *const _, 8);
+        }
+    }
+
+    /// Marks this `Arc` as intentionally leaked for the purposes of refcount
+    /// logging.
+    ///
+    /// It's a logic error to call this more than once, but it's not unsafe, as
+    /// it'd just report negative leaks.
+    #[inline(always)]
+    pub fn mark_as_intentionally_leaked(&self) {
+        self.record_drop();
+    }
+
+    // Non-inlined part of `drop`. Just invokes the destructor and calls the
+    // refcount logging machinery if enabled.
     #[inline(never)]
     unsafe fn drop_slow(&mut self) {
+        self.record_drop();
         let _ = Box::from_raw(self.ptr());
     }
 
@@ -308,6 +348,12 @@ impl<T: ?Sized> Arc<T> {
     }
 }
 
+#[cfg(all(feature = "gecko", debug_assertions))]
+extern "C" {
+    fn NS_LogCtor(aPtr: *const std::os::raw::c_void, aTypeName: *const std::os::raw::c_char, aSize: u32);
+    fn NS_LogDtor(aPtr: *const std::os::raw::c_void, aTypeName: *const std::os::raw::c_char, aSize: u32);
+}
+
 impl<T: ?Sized> Clone for Arc<T> {
     #[inline]
     fn clone(&self) -> Self {
@@ -612,7 +658,6 @@ impl<H, T> Arc<HeaderSlice<H, [T]>> {
         F: FnOnce(Layout) -> *mut u8,
         I: Iterator<Item = T> + ExactSizeIterator,
     {
-        use std::mem::{align_of, size_of};
         assert_ne!(size_of::<T>(), 0, "Need to think about ZST");
 
         let inner_align = align_of::<ArcInner<HeaderSlice<H, [T; 0]>>>();
@@ -700,6 +745,15 @@ impl<H, T> Arc<HeaderSlice<H, [T]>> {
             );
         }
 
+        #[cfg(all(feature = "gecko", debug_assertions))]
+        unsafe {
+            if !is_static {
+                // FIXME(emilio): Would be so amazing to have
+                // std::intrinsics::type_name() around.
+                NS_LogCtor(ptr as *const _, b"ServoArc\0".as_ptr() as *const _, 8)
+            }
+        }
+
         // Return the fat Arc.
         assert_eq!(
             size_of::<Self>(),

components/style/bloom.rs

@@ -19,7 +19,7 @@ thread_local! {
     /// such that they can be reused across style traversals. StyleBloom is responsible
     /// for ensuring that the bloom filter is zeroed when it is dropped.
     static BLOOM_KEY: Arc<AtomicRefCell<BloomFilter>> =
-              Arc::new(AtomicRefCell::new(BloomFilter::new()));
+        Arc::new_leaked(AtomicRefCell::new(BloomFilter::new()));
 }
 
 /// A struct that allows us to fast-reject deep descendant selectors avoiding

components/style/gecko/wrapper.rs

@@ -1736,7 +1736,7 @@ impl<'le> TElement for GeckoElement<'le> {
                     PropertyDeclaration::TextAlign(SpecifiedTextAlign::MozCenterOrInherit),
                     Importance::Normal,
                 );
-                let arc = Arc::new(global_style_data.shared_lock.wrap(pdb));
+                let arc = Arc::new_leaked(global_style_data.shared_lock.wrap(pdb));
                 ApplicableDeclarationBlock::from_declarations(arc, ServoCascadeLevel::PresHints)
             };
             static ref TABLE_COLOR_RULE: ApplicableDeclarationBlock = {
@@ -1745,7 +1745,7 @@ impl<'le> TElement for GeckoElement<'le> {
                     PropertyDeclaration::Color(SpecifiedColor(Color::InheritFromBodyQuirk.into())),
                     Importance::Normal,
                 );
-                let arc = Arc::new(global_style_data.shared_lock.wrap(pdb));
+                let arc = Arc::new_leaked(global_style_data.shared_lock.wrap(pdb));
                 ApplicableDeclarationBlock::from_declarations(arc, ServoCascadeLevel::PresHints)
             };
             static ref MATHML_LANG_RULE: ApplicableDeclarationBlock = {
@@ -1754,7 +1754,7 @@ impl<'le> TElement for GeckoElement<'le> {
                     PropertyDeclaration::XLang(SpecifiedLang(atom!("x-math"))),
                     Importance::Normal,
                 );
-                let arc = Arc::new(global_style_data.shared_lock.wrap(pdb));
+                let arc = Arc::new_leaked(global_style_data.shared_lock.wrap(pdb));
                 ApplicableDeclarationBlock::from_declarations(arc, ServoCascadeLevel::PresHints)
             };
             static ref SVG_TEXT_DISABLE_ZOOM_RULE: ApplicableDeclarationBlock = {
@@ -1763,7 +1763,7 @@ impl<'le> TElement for GeckoElement<'le> {
                     PropertyDeclaration::XTextZoom(SpecifiedZoom(false)),
                     Importance::Normal,
                 );
-                let arc = Arc::new(global_style_data.shared_lock.wrap(pdb));
+                let arc = Arc::new_leaked(global_style_data.shared_lock.wrap(pdb));
                 ApplicableDeclarationBlock::from_declarations(arc, ServoCascadeLevel::PresHints)
             };
         };

components/style/global_style_data.rs

@@ -125,7 +125,7 @@ lazy_static! {
     };
     /// Global style data
     pub static ref GLOBAL_STYLE_DATA: GlobalStyleData = GlobalStyleData {
-        shared_lock: SharedRwLock::new(),
+        shared_lock: SharedRwLock::new_leaked(),
         options: StyleSystemOptions::default(),
     };
 }

components/style/rule_tree/mod.rs

@@ -755,8 +755,7 @@ 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)]
+#[cfg(all(feature = "gecko", debug_assertions))]
 mod gecko_leak_checking {
     use super::RuleNode;
     use std::mem::size_of;
@@ -789,15 +788,13 @@ mod gecko_leak_checking {
 
 #[inline(always)]
 fn log_new(_ptr: *const RuleNode) {
-    #[cfg(feature = "gecko")]
-    #[cfg(debug_assertions)]
+    #[cfg(all(feature = "gecko", debug_assertions))]
     gecko_leak_checking::log_ctor(_ptr);
 }
 
 #[inline(always)]
 fn log_drop(_ptr: *const RuleNode) {
-    #[cfg(feature = "gecko")]
-    #[cfg(debug_assertions)]
+    #[cfg(all(feature = "gecko", debug_assertions))]
     gecko_leak_checking::log_dtor(_ptr);
 }
 

components/style/shared_lock.rs

@@ -71,6 +71,14 @@ impl SharedRwLock {
         }
     }
 
+    /// Create a new global shared lock (gecko).
+    #[cfg(feature = "gecko")]
+    pub fn new_leaked() -> Self {
+        SharedRwLock {
+            cell: Some(Arc::new_leaked(AtomicRefCell::new(SomethingZeroSizedButTyped))),
+        }
+    }
+
     /// Create a new read-only shared lock (gecko).
     #[cfg(feature = "gecko")]
     pub fn read_only() -> Self {

components/style/sharing/mod.rs

@@ -485,8 +485,12 @@ type SharingCache<E> = SharingCacheBase<StyleSharingCandidate<E>>;
 type TypelessSharingCache = SharingCacheBase<FakeCandidate>;
 type StoredSharingCache = Arc<AtomicRefCell<TypelessSharingCache>>;
 
-thread_local!(static SHARING_CACHE_KEY: StoredSharingCache =
-              Arc::new(AtomicRefCell::new(TypelessSharingCache::default())));
+thread_local! {
+    // TODO(emilio): Looks like a few of these should just be Rc<RefCell<>> or
+    // something. No need for atomics in the thread-local code.
+    static SHARING_CACHE_KEY: StoredSharingCache =
+        Arc::new_leaked(AtomicRefCell::new(TypelessSharingCache::default()));
+}
 
 /// An LRU cache of the last few nodes seen, so that we can aggressively try to
 /// reuse their styles.

components/style/values/computed/list.rs

@@ -10,7 +10,7 @@ pub use crate::values::specified::list::MozListReversed;
 pub use crate::values::specified::list::{QuotePair, Quotes};
 
 lazy_static! {
-    static ref INITIAL_QUOTES: crate::ArcSlice<QuotePair> = crate::ArcSlice::from_iter(
+    static ref INITIAL_QUOTES: crate::ArcSlice<QuotePair> = crate::ArcSlice::from_iter_leaked(
         vec![
             QuotePair {
                 opening: "\u{201c}".to_owned().into(),

components/style_traits/arc_slice.rs

@@ -40,7 +40,7 @@ impl<T> Deref for ArcSlice<T> {
 lazy_static! {
     // ThinArc doesn't support alignments greater than align_of::<u64>.
     static ref EMPTY_ARC_SLICE: ArcSlice<u64> = {
-        ArcSlice(ThinArc::from_header_and_iter(ARC_SLICE_CANARY, iter::empty()))
+        ArcSlice::from_iter_leaked(iter::empty())
     };
 }
 
@@ -74,6 +74,19 @@ impl<T> ArcSlice<T> {
         ArcSlice(ThinArc::from_header_and_iter(ARC_SLICE_CANARY, items))
     }
 
+    /// Creates an Arc for a slice using the given iterator to generate the
+    /// slice, and marks the arc as intentionally leaked from the refcount
+    /// logging point of view.
+    #[inline]
+    pub fn from_iter_leaked<I>(items: I) -> Self
+    where
+        I: Iterator<Item = T> + ExactSizeIterator,
+    {
+        let thin_arc = ThinArc::from_header_and_iter(ARC_SLICE_CANARY, items);
+        thin_arc.with_arc(|a| a.mark_as_intentionally_leaked());
+        ArcSlice(thin_arc)
+    }
+
     /// Creates a value that can be passed via FFI, and forgets this value
     /// altogether.
     #[inline]