mirror of
https://github.com/servo/servo.git
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61877b7316
This patch adds measurement of Selectors within StyleRule. This requires exposing the pointer within ThinArc. The patch also adds measurement of the several CssRule variants, in order to measure nested CssRules (and PropertyDeclarationBlocks) within them: DocumentRule, MediaRule, PageRule, SupportsRule.
968 lines
32 KiB
Rust
968 lines
32 KiB
Rust
// Copyright 2012-2014 The Rust Project Developers. See the COPYRIGHT
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// file at the top-level directory of this distribution and at
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// http://rust-lang.org/COPYRIGHT.
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//
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// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
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// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
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// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
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// option. This file may not be copied, modified, or distributed
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// except according to those terms.
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//! Fork of Arc for Servo. This has the following advantages over std::Arc:
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//! * We don't waste storage on the weak reference count.
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//! * We don't do extra RMU operations to handle the possibility of weak references.
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//! * We can experiment with arena allocation (todo).
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//! * We can add methods to support our custom use cases [1].
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//! * We have support for dynamically-sized types (see from_header_and_iter).
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//! * We have support for thin arcs to unsized types (see ThinArc).
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//!
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//! [1] https://bugzilla.mozilla.org/show_bug.cgi?id=1360883
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// The semantics of Arc are alread documented in the Rust docs, so we don't
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// duplicate those here.
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#![allow(missing_docs)]
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extern crate nodrop;
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#[cfg(feature = "servo")] extern crate serde;
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extern crate stable_deref_trait;
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#[cfg(feature = "servo")]
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use heapsize::HeapSizeOf;
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use nodrop::NoDrop;
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#[cfg(feature = "servo")]
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use serde::{Deserialize, Serialize};
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use stable_deref_trait::{CloneStableDeref, StableDeref};
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use std::{isize, usize};
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use std::borrow;
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use std::cmp::Ordering;
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use std::convert::From;
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use std::fmt;
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use std::hash::{Hash, Hasher};
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use std::iter::{ExactSizeIterator, Iterator};
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use std::mem;
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use std::ops::{Deref, DerefMut};
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use std::os::raw::c_void;
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use std::process;
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use std::ptr;
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use std::slice;
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use std::sync::atomic;
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use std::sync::atomic::Ordering::{Acquire, Relaxed, Release};
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// Private macro to get the offset of a struct field in bytes from the address of the struct.
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macro_rules! offset_of {
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($container:path, $field:ident) => {{
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// Make sure the field actually exists. This line ensures that a compile-time error is
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// generated if $field is accessed through a Deref impl.
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let $container { $field: _, .. };
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// Create an (invalid) instance of the container and calculate the offset to its
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// field. Using a null pointer might be UB if `&(*(0 as *const T)).field` is interpreted to
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// be nullptr deref.
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let invalid: $container = ::std::mem::uninitialized();
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let offset = &invalid.$field as *const _ as usize - &invalid as *const _ as usize;
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// Do not run destructors on the made up invalid instance.
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::std::mem::forget(invalid);
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offset as isize
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}};
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}
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/// A soft limit on the amount of references that may be made to an `Arc`.
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///
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/// Going above this limit will abort your program (although not
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/// necessarily) at _exactly_ `MAX_REFCOUNT + 1` references.
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const MAX_REFCOUNT: usize = (isize::MAX) as usize;
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/// Wrapper type for pointers to get the non-zero optimization. When
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/// NonZero/Shared/Unique are stabilized, we should just use Shared
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/// here to get the same effect. Gankro is working on this in [1].
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///
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/// It's unfortunate that this needs to infect all the caller types
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/// with 'static. It would be nice to just use a &() and a PhantomData<T>
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/// instead, but then the compiler can't determine whether the &() should
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/// be thin or fat (which depends on whether or not T is sized). Given
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/// that this is all a temporary hack, this restriction is fine for now.
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///
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/// [1] https://github.com/rust-lang/rust/issues/27730
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pub struct NonZeroPtrMut<T: ?Sized + 'static>(&'static mut T);
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impl<T: ?Sized> NonZeroPtrMut<T> {
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pub fn new(ptr: *mut T) -> Self {
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assert!(!(ptr as *mut u8).is_null());
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NonZeroPtrMut(unsafe { mem::transmute(ptr) })
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}
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pub fn ptr(&self) -> *mut T {
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self.0 as *const T as *mut T
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}
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}
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impl<T: ?Sized + 'static> Clone for NonZeroPtrMut<T> {
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fn clone(&self) -> Self {
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NonZeroPtrMut::new(self.ptr())
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}
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}
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impl<T: ?Sized + 'static> fmt::Pointer for NonZeroPtrMut<T> {
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fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
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fmt::Pointer::fmt(&self.ptr(), f)
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}
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}
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impl<T: ?Sized + 'static> fmt::Debug for NonZeroPtrMut<T> {
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fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
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<Self as fmt::Pointer>::fmt(self, f)
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}
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}
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impl<T: ?Sized + 'static> PartialEq for NonZeroPtrMut<T> {
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fn eq(&self, other: &Self) -> bool {
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self.ptr() == other.ptr()
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}
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}
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impl<T: ?Sized + 'static> Eq for NonZeroPtrMut<T> {}
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pub struct Arc<T: ?Sized + 'static> {
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p: NonZeroPtrMut<ArcInner<T>>,
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}
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/// An Arc that is known to be uniquely owned
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///
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/// This lets us build arcs that we can mutate before
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/// freezing, without needing to change the allocation
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pub struct UniqueArc<T: ?Sized + 'static>(Arc<T>);
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impl<T> UniqueArc<T> {
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#[inline]
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/// Construct a new UniqueArc
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pub fn new(data: T) -> Self {
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UniqueArc(Arc::new(data))
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}
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#[inline]
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/// Convert to a shareable Arc<T> once we're done using it
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pub fn shareable(self) -> Arc<T> {
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self.0
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}
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}
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impl<T> Deref for UniqueArc<T> {
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type Target = T;
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fn deref(&self) -> &T {
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&*self.0
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}
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}
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impl<T> DerefMut for UniqueArc<T> {
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fn deref_mut(&mut self) -> &mut T {
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// We know this to be uniquely owned
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unsafe { &mut (*self.0.ptr()).data }
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}
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}
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unsafe impl<T: ?Sized + Sync + Send> Send for Arc<T> {}
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unsafe impl<T: ?Sized + Sync + Send> Sync for Arc<T> {}
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struct ArcInner<T: ?Sized> {
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count: atomic::AtomicUsize,
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data: T,
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}
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unsafe impl<T: ?Sized + Sync + Send> Send for ArcInner<T> {}
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unsafe impl<T: ?Sized + Sync + Send> Sync for ArcInner<T> {}
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impl<T> Arc<T> {
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#[inline]
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pub fn new(data: T) -> Self {
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let x = Box::new(ArcInner {
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count: atomic::AtomicUsize::new(1),
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data: data,
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});
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Arc { p: NonZeroPtrMut::new(Box::into_raw(x)) }
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}
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pub fn into_raw(this: Self) -> *const T {
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let ptr = unsafe { &((*this.ptr()).data) as *const _ };
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mem::forget(this);
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ptr
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}
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pub unsafe fn from_raw(ptr: *const T) -> Self {
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// To find the corresponding pointer to the `ArcInner` we need
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// to subtract the offset of the `data` field from the pointer.
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let ptr = (ptr as *const u8).offset(-offset_of!(ArcInner<T>, data));
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Arc {
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p: NonZeroPtrMut::new(ptr as *mut ArcInner<T>),
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}
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}
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/// Produce a pointer to the data that can be converted back
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/// to an arc
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pub fn borrow_arc<'a>(&'a self) -> ArcBorrow<'a, T> {
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ArcBorrow(&**self)
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}
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/// Temporarily converts |self| into a bonafide RawOffsetArc and exposes it to the
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/// provided callback. The refcount is not modified.
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#[inline(always)]
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pub fn with_raw_offset_arc<F, U>(&self, f: F) -> U
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where F: FnOnce(&RawOffsetArc<T>) -> U
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{
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// Synthesize transient Arc, which never touches the refcount of the ArcInner.
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let transient = unsafe { NoDrop::new(Arc::into_raw_offset(ptr::read(self))) };
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// Expose the transient Arc to the callback, which may clone it if it wants.
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let result = f(&transient);
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// Forget the transient Arc to leave the refcount untouched.
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mem::forget(transient);
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// Forward the result.
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result
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}
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/// Returns the address on the heap of the Arc itself -- not the T within it -- for memory
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/// reporting.
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pub fn heap_ptr(&self) -> *const c_void {
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self.p.ptr() as *const ArcInner<T> as *const c_void
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}
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}
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impl<T: ?Sized> Arc<T> {
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#[inline]
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fn inner(&self) -> &ArcInner<T> {
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// This unsafety is ok because while this arc is alive we're guaranteed
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// that the inner pointer is valid. Furthermore, we know that the
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// `ArcInner` structure itself is `Sync` because the inner data is
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// `Sync` as well, so we're ok loaning out an immutable pointer to these
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// contents.
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unsafe { &*self.ptr() }
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}
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// Non-inlined part of `drop`. Just invokes the destructor.
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#[inline(never)]
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unsafe fn drop_slow(&mut self) {
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let _ = Box::from_raw(self.ptr());
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}
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#[inline]
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pub fn ptr_eq(this: &Self, other: &Self) -> bool {
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this.ptr() == other.ptr()
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}
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fn ptr(&self) -> *mut ArcInner<T> {
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self.p.ptr()
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}
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}
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impl<T: ?Sized> Clone for Arc<T> {
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#[inline]
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fn clone(&self) -> Self {
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// Using a relaxed ordering is alright here, as knowledge of the
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// original reference prevents other threads from erroneously deleting
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// the object.
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//
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// As explained in the [Boost documentation][1], Increasing the
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// reference counter can always be done with memory_order_relaxed: New
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// references to an object can only be formed from an existing
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// reference, and passing an existing reference from one thread to
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// another must already provide any required synchronization.
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//
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// [1]: (www.boost.org/doc/libs/1_55_0/doc/html/atomic/usage_examples.html)
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let old_size = self.inner().count.fetch_add(1, Relaxed);
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// However we need to guard against massive refcounts in case someone
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// is `mem::forget`ing Arcs. If we don't do this the count can overflow
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// and users will use-after free. We racily saturate to `isize::MAX` on
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// the assumption that there aren't ~2 billion threads incrementing
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// the reference count at once. This branch will never be taken in
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// any realistic program.
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//
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// We abort because such a program is incredibly degenerate, and we
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// don't care to support it.
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if old_size > MAX_REFCOUNT {
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process::abort();
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}
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Arc { p: NonZeroPtrMut::new(self.ptr()) }
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}
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}
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impl<T: ?Sized> Deref for Arc<T> {
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type Target = T;
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#[inline]
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fn deref(&self) -> &T {
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&self.inner().data
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}
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}
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impl<T: Clone> Arc<T> {
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#[inline]
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pub fn make_mut(this: &mut Self) -> &mut T {
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if !this.is_unique() {
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// Another pointer exists; clone
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*this = Arc::new((**this).clone());
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}
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unsafe {
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// This unsafety is ok because we're guaranteed that the pointer
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// returned is the *only* pointer that will ever be returned to T. Our
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// reference count is guaranteed to be 1 at this point, and we required
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// the Arc itself to be `mut`, so we're returning the only possible
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// reference to the inner data.
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&mut (*this.ptr()).data
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}
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}
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}
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impl<T: ?Sized> Arc<T> {
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#[inline]
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pub fn get_mut(this: &mut Self) -> Option<&mut T> {
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if this.is_unique() {
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unsafe {
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// See make_mut() for documentation of the threadsafety here.
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Some(&mut (*this.ptr()).data)
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}
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} else {
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None
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}
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}
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#[inline]
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fn is_unique(&self) -> bool {
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// We can use Relaxed here, but the justification is a bit subtle.
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//
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// The reason to use Acquire would be to synchronize with other threads
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// that are modifying the refcount with Release, i.e. to ensure that
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// their writes to memory guarded by this refcount are flushed. However,
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// we know that threads only modify the contents of the Arc when they
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// observe the refcount to be 1, and no other thread could observe that
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// because we're holding one strong reference here.
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self.inner().count.load(Relaxed) == 1
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}
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}
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impl<T: ?Sized> Drop for Arc<T> {
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#[inline]
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fn drop(&mut self) {
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// Because `fetch_sub` is already atomic, we do not need to synchronize
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// with other threads unless we are going to delete the object.
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if self.inner().count.fetch_sub(1, Release) != 1 {
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return;
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}
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// FIXME(bholley): Use the updated comment when [2] is merged.
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//
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// This load is needed to prevent reordering of use of the data and
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// deletion of the data. Because it is marked `Release`, the decreasing
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// of the reference count synchronizes with this `Acquire` load. This
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// means that use of the data happens before decreasing the reference
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// count, which happens before this load, which happens before the
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// deletion of the data.
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//
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// As explained in the [Boost documentation][1],
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//
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// > It is important to enforce any possible access to the object in one
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// > thread (through an existing reference) to *happen before* deleting
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// > the object in a different thread. This is achieved by a "release"
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// > operation after dropping a reference (any access to the object
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// > through this reference must obviously happened before), and an
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// > "acquire" operation before deleting the object.
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//
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// [1]: (www.boost.org/doc/libs/1_55_0/doc/html/atomic/usage_examples.html)
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// [2]: https://github.com/rust-lang/rust/pull/41714
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self.inner().count.load(Acquire);
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unsafe {
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self.drop_slow();
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}
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}
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}
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impl<T: ?Sized + PartialEq> PartialEq for Arc<T> {
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fn eq(&self, other: &Arc<T>) -> bool {
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*(*self) == *(*other)
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}
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fn ne(&self, other: &Arc<T>) -> bool {
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*(*self) != *(*other)
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}
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}
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impl<T: ?Sized + PartialOrd> PartialOrd for Arc<T> {
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fn partial_cmp(&self, other: &Arc<T>) -> Option<Ordering> {
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(**self).partial_cmp(&**other)
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}
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fn lt(&self, other: &Arc<T>) -> bool {
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*(*self) < *(*other)
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}
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fn le(&self, other: &Arc<T>) -> bool {
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*(*self) <= *(*other)
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}
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fn gt(&self, other: &Arc<T>) -> bool {
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*(*self) > *(*other)
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}
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fn ge(&self, other: &Arc<T>) -> bool {
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*(*self) >= *(*other)
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}
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}
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impl<T: ?Sized + Ord> Ord for Arc<T> {
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fn cmp(&self, other: &Arc<T>) -> Ordering {
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(**self).cmp(&**other)
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}
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}
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impl<T: ?Sized + Eq> Eq for Arc<T> {}
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impl<T: ?Sized + fmt::Display> fmt::Display for Arc<T> {
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fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
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fmt::Display::fmt(&**self, f)
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}
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}
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impl<T: ?Sized + fmt::Debug> fmt::Debug for Arc<T> {
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fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
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fmt::Debug::fmt(&**self, f)
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}
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}
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impl<T: ?Sized> fmt::Pointer for Arc<T> {
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fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
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fmt::Pointer::fmt(&self.ptr(), f)
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}
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}
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impl<T: Default> Default for Arc<T> {
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fn default() -> Arc<T> {
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Arc::new(Default::default())
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}
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}
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impl<T: ?Sized + Hash> Hash for Arc<T> {
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fn hash<H: Hasher>(&self, state: &mut H) {
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(**self).hash(state)
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}
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}
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impl<T> From<T> for Arc<T> {
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fn from(t: T) -> Self {
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Arc::new(t)
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}
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}
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impl<T: ?Sized> borrow::Borrow<T> for Arc<T> {
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fn borrow(&self) -> &T {
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&**self
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}
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}
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impl<T: ?Sized> AsRef<T> for Arc<T> {
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fn as_ref(&self) -> &T {
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&**self
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}
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}
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unsafe impl<T: ?Sized> StableDeref for Arc<T> {}
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unsafe impl<T: ?Sized> CloneStableDeref for Arc<T> {}
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|
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// This is what the HeapSize crate does for regular arc, but is questionably
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// sound. See https://github.com/servo/heapsize/issues/37
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#[cfg(feature = "servo")]
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impl<T: HeapSizeOf> HeapSizeOf for Arc<T> {
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fn heap_size_of_children(&self) -> usize {
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(**self).heap_size_of_children()
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}
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}
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#[cfg(feature = "servo")]
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impl<'de, T: Deserialize<'de>> Deserialize<'de> for Arc<T>
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{
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fn deserialize<D>(deserializer: D) -> Result<Arc<T>, D::Error>
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where
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D: ::serde::de::Deserializer<'de>,
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{
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T::deserialize(deserializer).map(Arc::new)
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}
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}
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#[cfg(feature = "servo")]
|
|
impl<T: Serialize> Serialize for Arc<T>
|
|
{
|
|
fn serialize<S>(&self, serializer: S) -> Result<S::Ok, S::Error>
|
|
where
|
|
S: ::serde::ser::Serializer,
|
|
{
|
|
(**self).serialize(serializer)
|
|
}
|
|
}
|
|
|
|
/// Structure to allow Arc-managing some fixed-sized data and a variably-sized
|
|
/// slice in a single allocation.
|
|
#[derive(Debug, Eq, PartialEq, PartialOrd)]
|
|
pub struct HeaderSlice<H, T: ?Sized> {
|
|
/// The fixed-sized data.
|
|
pub header: H,
|
|
|
|
/// The dynamically-sized data.
|
|
pub slice: T,
|
|
}
|
|
|
|
#[inline(always)]
|
|
fn divide_rounding_up(dividend: usize, divisor: usize) -> usize {
|
|
(dividend + divisor - 1) / divisor
|
|
}
|
|
|
|
impl<H, T> Arc<HeaderSlice<H, [T]>> {
|
|
/// Creates an Arc for a HeaderSlice using the given header struct and
|
|
/// iterator to generate the slice. The resulting Arc will be fat.
|
|
#[inline]
|
|
pub fn from_header_and_iter<I>(header: H, mut items: I) -> Self
|
|
where I: Iterator<Item=T> + ExactSizeIterator
|
|
{
|
|
use ::std::mem::size_of;
|
|
assert!(size_of::<T>() != 0, "Need to think about ZST");
|
|
|
|
// Compute the required size for the allocation.
|
|
let num_items = items.len();
|
|
let size = {
|
|
// First, determine the alignment of a hypothetical pointer to a
|
|
// HeaderSlice.
|
|
let fake_slice_ptr_align: usize = mem::align_of::<ArcInner<HeaderSlice<H, [T; 1]>>>();
|
|
|
|
// Next, synthesize a totally garbage (but properly aligned) pointer
|
|
// to a sequence of T.
|
|
let fake_slice_ptr = fake_slice_ptr_align as *const T;
|
|
|
|
// Convert that sequence to a fat pointer. The address component of
|
|
// the fat pointer will be garbage, but the length will be correct.
|
|
let fake_slice = unsafe { slice::from_raw_parts(fake_slice_ptr, num_items) };
|
|
|
|
// Pretend the garbage address points to our allocation target (with
|
|
// a trailing sequence of T), rather than just a sequence of T.
|
|
let fake_ptr = fake_slice as *const [T] as *const ArcInner<HeaderSlice<H, [T]>>;
|
|
let fake_ref: &ArcInner<HeaderSlice<H, [T]>> = unsafe { &*fake_ptr };
|
|
|
|
// Use size_of_val, which will combine static information about the
|
|
// type with the length from the fat pointer. The garbage address
|
|
// will not be used.
|
|
mem::size_of_val(fake_ref)
|
|
};
|
|
|
|
let ptr: *mut ArcInner<HeaderSlice<H, [T]>>;
|
|
unsafe {
|
|
// Allocate the buffer. We use Vec because the underlying allocation
|
|
// machinery isn't available in stable Rust.
|
|
//
|
|
// To avoid alignment issues, we allocate words rather than bytes,
|
|
// rounding up to the nearest word size.
|
|
let buffer = if mem::align_of::<T>() <= mem::align_of::<usize>() {
|
|
Self::allocate_buffer::<usize>(size)
|
|
} else if mem::align_of::<T>() <= mem::align_of::<u64>() {
|
|
// On 32-bit platforms <T> may have 8 byte alignment while usize has 4 byte aligment.
|
|
// Use u64 to avoid over-alignment.
|
|
// This branch will compile away in optimized builds.
|
|
Self::allocate_buffer::<u64>(size)
|
|
} else {
|
|
panic!("Over-aligned type not handled");
|
|
};
|
|
|
|
// Synthesize the fat pointer. We do this by claiming we have a direct
|
|
// pointer to a [T], and then changing the type of the borrow. The key
|
|
// point here is that the length portion of the fat pointer applies
|
|
// only to the number of elements in the dynamically-sized portion of
|
|
// the type, so the value will be the same whether it points to a [T]
|
|
// or something else with a [T] as its last member.
|
|
let fake_slice: &mut [T] = slice::from_raw_parts_mut(buffer as *mut T, num_items);
|
|
ptr = fake_slice as *mut [T] as *mut ArcInner<HeaderSlice<H, [T]>>;
|
|
|
|
// Write the data.
|
|
//
|
|
// Note that any panics here (i.e. from the iterator) are safe, since
|
|
// we'll just leak the uninitialized memory.
|
|
ptr::write(&mut ((*ptr).count), atomic::AtomicUsize::new(1));
|
|
ptr::write(&mut ((*ptr).data.header), header);
|
|
let mut current: *mut T = &mut (*ptr).data.slice[0];
|
|
for _ in 0..num_items {
|
|
ptr::write(current, items.next().expect("ExactSizeIterator over-reported length"));
|
|
current = current.offset(1);
|
|
}
|
|
assert!(items.next().is_none(), "ExactSizeIterator under-reported length");
|
|
|
|
// We should have consumed the buffer exactly.
|
|
debug_assert!(current as *mut u8 == buffer.offset(size as isize));
|
|
}
|
|
|
|
// Return the fat Arc.
|
|
assert_eq!(size_of::<Self>(), size_of::<usize>() * 2, "The Arc will be fat");
|
|
Arc { p: NonZeroPtrMut::new(ptr) }
|
|
}
|
|
|
|
#[inline]
|
|
unsafe fn allocate_buffer<W>(size: usize) -> *mut u8 {
|
|
let words_to_allocate = divide_rounding_up(size, mem::size_of::<W>());
|
|
let mut vec = Vec::<W>::with_capacity(words_to_allocate);
|
|
vec.set_len(words_to_allocate);
|
|
Box::into_raw(vec.into_boxed_slice()) as *mut W as *mut u8
|
|
}
|
|
}
|
|
|
|
/// Header data with an inline length. Consumers that use HeaderWithLength as the
|
|
/// Header type in HeaderSlice can take advantage of ThinArc.
|
|
#[derive(Debug, Eq, PartialEq, PartialOrd)]
|
|
pub struct HeaderWithLength<H> {
|
|
/// The fixed-sized data.
|
|
pub header: H,
|
|
|
|
/// The slice length.
|
|
length: usize,
|
|
}
|
|
|
|
impl<H> HeaderWithLength<H> {
|
|
/// Creates a new HeaderWithLength.
|
|
pub fn new(header: H, length: usize) -> Self {
|
|
HeaderWithLength {
|
|
header: header,
|
|
length: length,
|
|
}
|
|
}
|
|
}
|
|
|
|
type HeaderSliceWithLength<H, T> = HeaderSlice<HeaderWithLength<H>, T>;
|
|
pub struct ThinArc<H: 'static, T: 'static> {
|
|
ptr: *mut ArcInner<HeaderSliceWithLength<H, [T; 1]>>,
|
|
}
|
|
|
|
unsafe impl<H: Sync + Send, T: Sync + Send> Send for ThinArc<H, T> {}
|
|
unsafe impl<H: Sync + Send, T: Sync + Send> Sync for ThinArc<H, T> {}
|
|
|
|
// Synthesize a fat pointer from a thin pointer.
|
|
//
|
|
// See the comment around the analogous operation in from_header_and_iter.
|
|
fn thin_to_thick<H, T>(thin: *mut ArcInner<HeaderSliceWithLength<H, [T; 1]>>)
|
|
-> *mut ArcInner<HeaderSliceWithLength<H, [T]>>
|
|
{
|
|
let len = unsafe { (*thin).data.header.length };
|
|
let fake_slice: *mut [T] = unsafe {
|
|
slice::from_raw_parts_mut(thin as *mut T, len)
|
|
};
|
|
|
|
fake_slice as *mut ArcInner<HeaderSliceWithLength<H, [T]>>
|
|
}
|
|
|
|
impl<H: 'static, T: 'static> ThinArc<H, T> {
|
|
/// Temporarily converts |self| into a bonafide Arc and exposes it to the
|
|
/// provided callback. The refcount is not modified.
|
|
#[inline(always)]
|
|
pub fn with_arc<F, U>(&self, f: F) -> U
|
|
where F: FnOnce(&Arc<HeaderSliceWithLength<H, [T]>>) -> U
|
|
{
|
|
// Synthesize transient Arc, which never touches the refcount of the ArcInner.
|
|
let transient = NoDrop::new(Arc {
|
|
p: NonZeroPtrMut::new(thin_to_thick(self.ptr))
|
|
});
|
|
|
|
// Expose the transient Arc to the callback, which may clone it if it wants.
|
|
let result = f(&transient);
|
|
|
|
// Forget the transient Arc to leave the refcount untouched.
|
|
// XXXManishearth this can be removed when unions stabilize,
|
|
// since then NoDrop becomes zero overhead
|
|
mem::forget(transient);
|
|
|
|
// Forward the result.
|
|
result
|
|
}
|
|
|
|
/// Returns the address on the heap of the ThinArc itself -- not the T
|
|
/// within it -- for memory reporting.
|
|
pub fn heap_ptr(&self) -> *const c_void {
|
|
self.ptr as *const ArcInner<T> as *const c_void
|
|
}
|
|
}
|
|
|
|
impl<H, T> Deref for ThinArc<H, T> {
|
|
type Target = HeaderSliceWithLength<H, [T]>;
|
|
fn deref(&self) -> &Self::Target {
|
|
unsafe { &(*thin_to_thick(self.ptr)).data }
|
|
}
|
|
}
|
|
|
|
impl<H: 'static, T: 'static> Clone for ThinArc<H, T> {
|
|
fn clone(&self) -> Self {
|
|
ThinArc::with_arc(self, |a| Arc::into_thin(a.clone()))
|
|
}
|
|
}
|
|
|
|
impl<H: 'static, T: 'static> Drop for ThinArc<H, T> {
|
|
fn drop(&mut self) {
|
|
let _ = Arc::from_thin(ThinArc { ptr: self.ptr });
|
|
}
|
|
}
|
|
|
|
impl<H: 'static, T: 'static> Arc<HeaderSliceWithLength<H, [T]>> {
|
|
/// Converts an Arc into a ThinArc. This consumes the Arc, so the refcount
|
|
/// is not modified.
|
|
pub fn into_thin(a: Self) -> ThinArc<H, T> {
|
|
assert!(a.header.length == a.slice.len(),
|
|
"Length needs to be correct for ThinArc to work");
|
|
let fat_ptr: *mut ArcInner<HeaderSliceWithLength<H, [T]>> = a.ptr();
|
|
mem::forget(a);
|
|
let thin_ptr = fat_ptr as *mut [usize] as *mut usize;
|
|
ThinArc {
|
|
ptr: thin_ptr as *mut ArcInner<HeaderSliceWithLength<H, [T; 1]>>
|
|
}
|
|
}
|
|
|
|
/// Converts a ThinArc into an Arc. This consumes the ThinArc, so the refcount
|
|
/// is not modified.
|
|
pub fn from_thin(a: ThinArc<H, T>) -> Self {
|
|
let ptr = thin_to_thick(a.ptr);
|
|
mem::forget(a);
|
|
Arc {
|
|
p: NonZeroPtrMut::new(ptr)
|
|
}
|
|
}
|
|
}
|
|
|
|
impl<H: PartialEq + 'static, T: PartialEq + 'static> PartialEq for ThinArc<H, T> {
|
|
fn eq(&self, other: &ThinArc<H, T>) -> bool {
|
|
ThinArc::with_arc(self, |a| {
|
|
ThinArc::with_arc(other, |b| {
|
|
*a == *b
|
|
})
|
|
})
|
|
}
|
|
}
|
|
|
|
impl<H: Eq + 'static, T: Eq + 'static> Eq for ThinArc<H, T> {}
|
|
|
|
/// An Arc, except it holds a pointer to the T instead of to the
|
|
/// entire ArcInner.
|
|
///
|
|
/// ```text
|
|
/// Arc<T> RawOffsetArc<T>
|
|
/// | |
|
|
/// v v
|
|
/// ---------------------
|
|
/// | RefCount | T (data) | [ArcInner<T>]
|
|
/// ---------------------
|
|
/// ```
|
|
///
|
|
/// This means that this is a direct pointer to
|
|
/// its contained data (and can be read from by both C++ and Rust),
|
|
/// but we can also convert it to a "regular" Arc<T> by removing the offset
|
|
#[derive(Eq)]
|
|
pub struct RawOffsetArc<T: 'static> {
|
|
ptr: NonZeroPtrMut<T>,
|
|
}
|
|
|
|
unsafe impl<T: 'static + Sync + Send> Send for RawOffsetArc<T> {}
|
|
unsafe impl<T: 'static + Sync + Send> Sync for RawOffsetArc<T> {}
|
|
|
|
impl<T: 'static> Deref for RawOffsetArc<T> {
|
|
type Target = T;
|
|
fn deref(&self) -> &Self::Target {
|
|
unsafe { &*self.ptr.ptr() }
|
|
}
|
|
}
|
|
|
|
impl<T: 'static> Clone for RawOffsetArc<T> {
|
|
fn clone(&self) -> Self {
|
|
Arc::into_raw_offset(self.clone_arc())
|
|
}
|
|
}
|
|
|
|
impl<T: 'static> Drop for RawOffsetArc<T> {
|
|
fn drop(&mut self) {
|
|
let _ = Arc::from_raw_offset(RawOffsetArc { ptr: self.ptr.clone() });
|
|
}
|
|
}
|
|
|
|
|
|
impl<T: fmt::Debug + 'static> fmt::Debug for RawOffsetArc<T> {
|
|
fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
|
|
fmt::Debug::fmt(&**self, f)
|
|
}
|
|
}
|
|
|
|
impl<T: PartialEq> PartialEq for RawOffsetArc<T> {
|
|
fn eq(&self, other: &RawOffsetArc<T>) -> bool {
|
|
*(*self) == *(*other)
|
|
}
|
|
|
|
fn ne(&self, other: &RawOffsetArc<T>) -> bool {
|
|
*(*self) != *(*other)
|
|
}
|
|
}
|
|
|
|
impl<T: 'static> RawOffsetArc<T> {
|
|
/// Temporarily converts |self| into a bonafide Arc and exposes it to the
|
|
/// provided callback. The refcount is not modified.
|
|
#[inline(always)]
|
|
pub fn with_arc<F, U>(&self, f: F) -> U
|
|
where F: FnOnce(&Arc<T>) -> U
|
|
{
|
|
// Synthesize transient Arc, which never touches the refcount of the ArcInner.
|
|
let transient = unsafe { NoDrop::new(Arc::from_raw(self.ptr.ptr())) };
|
|
|
|
// Expose the transient Arc to the callback, which may clone it if it wants.
|
|
let result = f(&transient);
|
|
|
|
// Forget the transient Arc to leave the refcount untouched.
|
|
// XXXManishearth this can be removed when unions stabilize,
|
|
// since then NoDrop becomes zero overhead
|
|
mem::forget(transient);
|
|
|
|
// Forward the result.
|
|
result
|
|
}
|
|
|
|
/// If uniquely owned, provide a mutable reference
|
|
/// Else create a copy, and mutate that
|
|
pub fn make_mut(&mut self) -> &mut T where T: Clone {
|
|
unsafe {
|
|
// extract the RawOffsetArc as an owned variable
|
|
let this = ptr::read(self);
|
|
// treat it as a real Arc
|
|
let mut arc = Arc::from_raw_offset(this);
|
|
// obtain the mutable reference. Cast away the lifetime
|
|
// This may mutate `arc`
|
|
let ret = Arc::make_mut(&mut arc) as *mut _;
|
|
// Store the possibly-mutated arc back inside, after converting
|
|
// it to a RawOffsetArc again
|
|
ptr::write(self, Arc::into_raw_offset(arc));
|
|
&mut *ret
|
|
}
|
|
}
|
|
|
|
/// Clone it as an Arc
|
|
pub fn clone_arc(&self) -> Arc<T> {
|
|
RawOffsetArc::with_arc(self, |a| a.clone())
|
|
}
|
|
|
|
/// Produce a pointer to the data that can be converted back
|
|
/// to an arc
|
|
pub fn borrow_arc<'a>(&'a self) -> ArcBorrow<'a, T> {
|
|
ArcBorrow(&**self)
|
|
}
|
|
}
|
|
|
|
impl<T: 'static> Arc<T> {
|
|
/// Converts an Arc into a RawOffsetArc. This consumes the Arc, so the refcount
|
|
/// is not modified.
|
|
#[inline]
|
|
pub fn into_raw_offset(a: Self) -> RawOffsetArc<T> {
|
|
RawOffsetArc {
|
|
ptr: NonZeroPtrMut::new(Arc::into_raw(a) as *mut T),
|
|
}
|
|
}
|
|
|
|
/// Converts a RawOffsetArc into an Arc. This consumes the RawOffsetArc, so the refcount
|
|
/// is not modified.
|
|
#[inline]
|
|
pub fn from_raw_offset(a: RawOffsetArc<T>) -> Self {
|
|
let ptr = a.ptr.ptr();
|
|
mem::forget(a);
|
|
unsafe { Arc::from_raw(ptr) }
|
|
}
|
|
}
|
|
|
|
/// A "borrowed Arc". This is a pointer to
|
|
/// a T that is known to have been allocated within an
|
|
/// Arc.
|
|
///
|
|
/// This is equivalent in guarantees to `&Arc<T>`, however it is
|
|
/// a bit more flexible. To obtain an `&Arc<T>` you must have
|
|
/// an Arc<T> instance somewhere pinned down until we're done with it.
|
|
///
|
|
/// However, Gecko hands us refcounted things as pointers to T directly,
|
|
/// so we have to conjure up a temporary Arc on the stack each time. The
|
|
/// same happens for when the object is managed by a RawOffsetArc.
|
|
///
|
|
/// ArcBorrow lets us deal with borrows of known-refcounted objects
|
|
/// without needing to worry about how they're actually stored.
|
|
#[derive(Eq, PartialEq)]
|
|
pub struct ArcBorrow<'a, T: 'a>(&'a T);
|
|
|
|
impl<'a, T> Copy for ArcBorrow<'a, T> {}
|
|
impl<'a, T> Clone for ArcBorrow<'a, T> {
|
|
fn clone(&self) -> Self {
|
|
*self
|
|
}
|
|
}
|
|
|
|
impl<'a, T> ArcBorrow<'a, T> {
|
|
pub fn clone_arc(&self) -> Arc<T> {
|
|
let arc = unsafe { Arc::from_raw(self.0) };
|
|
// addref it!
|
|
mem::forget(arc.clone());
|
|
arc
|
|
}
|
|
|
|
/// For constructing from a reference known to be Arc-backed,
|
|
/// e.g. if we obtain such a reference over FFI
|
|
pub unsafe fn from_ref(r: &'a T) -> Self {
|
|
ArcBorrow(r)
|
|
}
|
|
|
|
pub fn with_arc<F, U>(&self, f: F) -> U where F: FnOnce(&Arc<T>) -> U, T: 'static {
|
|
// Synthesize transient Arc, which never touches the refcount.
|
|
let transient = unsafe { NoDrop::new(Arc::from_raw(self.0)) };
|
|
|
|
// Expose the transient Arc to the callback, which may clone it if it wants.
|
|
let result = f(&transient);
|
|
|
|
// Forget the transient Arc to leave the refcount untouched.
|
|
// XXXManishearth this can be removed when unions stabilize,
|
|
// since then NoDrop becomes zero overhead
|
|
mem::forget(transient);
|
|
|
|
// Forward the result.
|
|
result
|
|
}
|
|
}
|
|
|
|
impl<'a, T> Deref for ArcBorrow<'a, T> {
|
|
type Target = T;
|
|
fn deref(&self) -> &T {
|
|
&*self.0
|
|
}
|
|
}
|
|
|
|
#[cfg(test)]
|
|
mod tests {
|
|
use std::clone::Clone;
|
|
use std::ops::Drop;
|
|
use std::sync::atomic;
|
|
use std::sync::atomic::Ordering::{Acquire, SeqCst};
|
|
use super::{Arc, HeaderWithLength, ThinArc};
|
|
|
|
#[derive(PartialEq)]
|
|
struct Canary(*mut atomic::AtomicUsize);
|
|
|
|
impl Drop for Canary {
|
|
fn drop(&mut self) {
|
|
unsafe { (*self.0).fetch_add(1, SeqCst); }
|
|
}
|
|
}
|
|
|
|
#[test]
|
|
fn slices_and_thin() {
|
|
let mut canary = atomic::AtomicUsize::new(0);
|
|
let c = Canary(&mut canary as *mut atomic::AtomicUsize);
|
|
let v = vec![5, 6];
|
|
let header = HeaderWithLength::new(c, v.len());
|
|
{
|
|
let x = Arc::into_thin(Arc::from_header_and_iter(header, v.into_iter()));
|
|
let y = ThinArc::with_arc(&x, |q| q.clone());
|
|
let _ = y.clone();
|
|
let _ = x == x;
|
|
Arc::from_thin(x.clone());
|
|
}
|
|
assert!(canary.load(Acquire) == 1);
|
|
}
|
|
}
|