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//! Thread-local garbage-collected boxes (The `Gc<T>` type). //! //! The `Gc<T>` type provides shared ownership of an immutable value. //! It is marked as non-sendable because the garbage collection only occurs //! thread-locally. #![cfg_attr(feature = "nightly", feature(coerce_unsized, unsize))] use crate::gc::{GcBox, GcBoxHeader}; use std::alloc::Layout; use std::cell::{Cell, UnsafeCell}; use std::cmp::Ordering; use std::fmt::{self, Debug, Display}; use std::hash::{Hash, Hasher}; use std::marker::PhantomData; use std::mem; use std::ops::{Deref, DerefMut}; use std::ptr::{self, NonNull}; use std::rc::Rc; #[cfg(feature = "nightly")] use std::marker::Unsize; #[cfg(feature = "nightly")] use std::ops::CoerceUnsized; mod gc; mod trace; #[cfg(feature = "derive")] pub use gc_derive::{Finalize, Trace}; // We re-export the Trace method, as well as some useful internal methods for // managing collections or configuring the garbage collector. pub use crate::gc::{finalizer_safe, force_collect}; pub use crate::trace::{Finalize, Trace}; //////// // Gc // //////// /// A garbage-collected pointer type over an immutable value. /// /// See the [module level documentation](./) for more details. pub struct Gc<T: Trace + ?Sized + 'static> { ptr_root: Cell<NonNull<GcBox<T>>>, marker: PhantomData<Rc<T>>, } #[cfg(feature = "nightly")] impl<T: Trace + ?Sized + Unsize<U>, U: Trace + ?Sized> CoerceUnsized<Gc<U>> for Gc<T> {} impl<T: Trace> Gc<T> { /// Constructs a new `Gc<T>` with the given value. /// /// # Collection /// /// This method could trigger a garbage collection. /// /// # Examples /// /// ``` /// use gc::Gc; /// /// let five = Gc::new(5); /// assert_eq!(*five, 5); /// ``` pub fn new(value: T) -> Self { assert!(mem::align_of::<GcBox<T>>() > 1); unsafe { // Allocate the memory for the object let ptr = GcBox::new(value); // When we create a Gc<T>, all pointers which have been moved to the // heap no longer need to be rooted, so we unroot them. (*ptr.as_ptr()).value().unroot(); let gc = Gc { ptr_root: Cell::new(NonNull::new_unchecked(ptr.as_ptr())), marker: PhantomData, }; gc.set_root(); gc } } } impl<T: Trace + ?Sized> Gc<T> { /// Returns `true` if the two `Gc`s point to the same allocation. pub fn ptr_eq(this: &Gc<T>, other: &Gc<T>) -> bool { GcBox::ptr_eq(this.inner(), other.inner()) } } /// Returns the given pointer with its root bit cleared. unsafe fn clear_root_bit<T: ?Sized + Trace>(ptr: NonNull<GcBox<T>>) -> NonNull<GcBox<T>> { let mut ptr = ptr.as_ptr(); *(&mut ptr as *mut _ as *mut usize) &= !1; // *(&mut ptr as *mut *const GcBox<T> as *mut usize) &= !1; NonNull::new_unchecked(ptr) } impl<T: Trace + ?Sized> Gc<T> { fn rooted(&self) -> bool { self.ptr_root.get().as_ptr() as *mut u8 as usize & 1 != 0 } unsafe fn set_root(&self) { let mut ptr = self.ptr_root.get().as_ptr(); *(&mut ptr as *mut *mut GcBox<T> as *mut usize) |= 1; self.ptr_root.set(NonNull::new_unchecked(ptr)); } unsafe fn clear_root(&self) { self.ptr_root.set(clear_root_bit(self.ptr_root.get())); } #[inline] fn inner(&self) -> &GcBox<T> { // If we are currently in the dropping phase of garbage collection, // it would be undefined behavior to dereference this pointer. // By opting into `Trace` you agree to not dereference this pointer // within your drop method, meaning that it should be safe. // // This assert exists just in case. assert!(finalizer_safe()); unsafe { &*clear_root_bit(self.ptr_root.get()).as_ptr() } } } impl<T: Trace + ?Sized> Gc<T> { /// Consumes the `Gc`, returning the wrapped pointer. /// /// To avoid a memory leak, the pointer must be converted back into a `Gc` /// using [`Gc::from_raw`][from_raw]. /// /// [from_raw]: struct.Gc.html#method.from_raw /// /// # Examples /// /// ``` /// use gc::Gc; /// /// let x = Gc::new(22); /// let x_ptr = Gc::into_raw(x); /// assert_eq!(unsafe { *x_ptr }, 22); /// ``` pub fn into_raw(this: Self) -> *const T { let ptr: *const T = &*this; mem::forget(this); ptr } /// Constructs an `Gc` from a raw pointer. /// /// The raw pointer must have been previously returned by a call to a /// [`Gc::into_raw`][into_raw]. /// /// This function is unsafe because improper use may lead to memory /// problems. For example, a use-after-free will occur if the function is /// called twice on the same raw pointer. /// /// [into_raw]: struct.Gc.html#method.into_raw /// /// # Examples /// /// ``` /// use gc::Gc; /// /// let x = Gc::new(22); /// let x_ptr = Gc::into_raw(x); /// /// unsafe { /// // Convert back to an `Gc` to prevent leak. /// let x = Gc::from_raw(x_ptr); /// assert_eq!(*x, 22); /// /// // Further calls to `Gc::from_raw(x_ptr)` would be memory unsafe. /// } /// /// // The memory can be freed at any time after `x` went out of scope above /// // (when the collector is run), which would result in `x_ptr` dangling! /// ``` pub unsafe fn from_raw(ptr: *const T) -> Self { // Find the offset of T in GcBox<T>. Note that Layout::extend // relies on GcBox being repr(C). let (_, offset) = Layout::new::<GcBoxHeader>() .extend(Layout::for_value::<T>(&*ptr)) .unwrap(); // Reverse the offset to find the original GcBox. let fake_ptr = ptr as *mut GcBox<T>; let rc_ptr = set_data_ptr(fake_ptr, (ptr as *mut u8).offset(-(offset as isize))); let gc = Gc { ptr_root: Cell::new(NonNull::new_unchecked(rc_ptr)), marker: PhantomData, }; gc.set_root(); gc } } impl<T: Trace + ?Sized> Finalize for Gc<T> {} unsafe impl<T: Trace + ?Sized> Trace for Gc<T> { #[inline] unsafe fn trace(&self) { self.inner().trace_inner(); } #[inline] unsafe fn root(&self) { assert!(!self.rooted(), "Can't double-root a Gc<T>"); // Try to get inner before modifying our state. Inner may be // inaccessible due to this method being invoked during the sweeping // phase, and we don't want to modify our state before panicking. self.inner().root_inner(); self.set_root(); } #[inline] unsafe fn unroot(&self) { assert!(self.rooted(), "Can't double-unroot a Gc<T>"); // Try to get inner before modifying our state. Inner may be // inaccessible due to this method being invoked during the sweeping // phase, and we don't want to modify our state before panicking. self.inner().unroot_inner(); self.clear_root(); } #[inline] fn finalize_glue(&self) { Finalize::finalize(self); } } impl<T: Trace + ?Sized> Clone for Gc<T> { #[inline] fn clone(&self) -> Self { unsafe { self.inner().root_inner(); let gc = Gc { ptr_root: Cell::new(self.ptr_root.get()), marker: PhantomData, }; gc.set_root(); gc } } } impl<T: Trace + ?Sized> Deref for Gc<T> { type Target = T; #[inline] fn deref(&self) -> &T { &self.inner().value() } } impl<T: Trace + ?Sized> Drop for Gc<T> { #[inline] fn drop(&mut self) { // If this pointer was a root, we should unroot it. if self.rooted() { unsafe { self.inner().unroot_inner(); } } } } impl<T: Trace + Default> Default for Gc<T> { #[inline] fn default() -> Self { Self::new(Default::default()) } } impl<T: Trace + ?Sized + PartialEq> PartialEq for Gc<T> { #[inline(always)] fn eq(&self, other: &Self) -> bool { **self == **other } } impl<T: Trace + ?Sized + Eq> Eq for Gc<T> {} impl<T: Trace + ?Sized + PartialOrd> PartialOrd for Gc<T> { #[inline(always)] fn partial_cmp(&self, other: &Self) -> Option<Ordering> { (**self).partial_cmp(&**other) } #[inline(always)] fn lt(&self, other: &Self) -> bool { **self < **other } #[inline(always)] fn le(&self, other: &Self) -> bool { **self <= **other } #[inline(always)] fn gt(&self, other: &Self) -> bool { **self > **other } #[inline(always)] fn ge(&self, other: &Self) -> bool { **self >= **other } } impl<T: Trace + ?Sized + Ord> Ord for Gc<T> { #[inline] fn cmp(&self, other: &Self) -> Ordering { (**self).cmp(&**other) } } impl<T: Trace + ?Sized + Hash> Hash for Gc<T> { fn hash<H: Hasher>(&self, state: &mut H) { (**self).hash(state); } } impl<T: Trace + ?Sized + Display> Display for Gc<T> { fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result { Display::fmt(&**self, f) } } impl<T: Trace + ?Sized + Debug> Debug for Gc<T> { fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result { Debug::fmt(&**self, f) } } impl<T: Trace + ?Sized> fmt::Pointer for Gc<T> { fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result { fmt::Pointer::fmt(&self.inner(), f) } } impl<T: Trace> From<T> for Gc<T> { fn from(t: T) -> Self { Self::new(t) } } impl<T: Trace + ?Sized> std::borrow::Borrow<T> for Gc<T> { fn borrow(&self) -> &T { &**self } } impl<T: Trace + ?Sized> std::convert::AsRef<T> for Gc<T> { fn as_ref(&self) -> &T { &**self } } //////////// // GcCell // //////////// /// The BorrowFlag used by GC is split into 2 parts. the upper 63 or 31 bits /// (depending on the architecture) are used to store the number of borrowed /// references to the type. The low bit is used to record the rootedness of the /// type. /// /// This means that GcCell can have, at maximum, half as many outstanding /// borrows as RefCell before panicking. I don't think that will be a problem. #[derive(Copy, Clone)] struct BorrowFlag(usize); #[derive(Copy, Clone, Debug, Eq, PartialEq)] enum BorrowState { Reading, Writing, Unused, } const ROOT: usize = 1; const WRITING: usize = !1; const UNUSED: usize = 0; /// The base borrowflag init is rooted, and has no outstanding borrows. const BORROWFLAG_INIT: BorrowFlag = BorrowFlag(1); impl BorrowFlag { fn borrowed(self) -> BorrowState { match self.0 & !ROOT { UNUSED => BorrowState::Unused, WRITING => BorrowState::Writing, _ => BorrowState::Reading, } } fn rooted(self) -> bool { match self.0 & ROOT { 0 => false, _ => true, } } fn set_writing(self) -> Self { // Set every bit other than the root bit, which is preserved BorrowFlag(self.0 | WRITING) } fn set_unused(self) -> Self { // Clear every bit other than the root bit, which is preserved BorrowFlag(self.0 & ROOT) } fn add_reading(self) -> Self { assert!(self.borrowed() != BorrowState::Writing); // Add 1 to the integer starting at the second binary digit. As our // borrowstate is not writing, we know that overflow cannot happen, so // this is equivalent to the following, more complicated, expression: // // BorrowFlag((self.0 & ROOT) | (((self.0 >> 1) + 1) << 1)) BorrowFlag(self.0 + 0b10) } fn sub_reading(self) -> Self { assert!(self.borrowed() == BorrowState::Reading); // Subtract 1 from the integer starting at the second binary digit. As // our borrowstate is not writing or unused, we know that overflow or // undeflow cannot happen, so this is equivalent to the following, more // complicated, expression: // // BorrowFlag((self.0 & ROOT) | (((self.0 >> 1) - 1) << 1)) BorrowFlag(self.0 - 0b10) } fn set_rooted(self, rooted: bool) -> Self { // Preserve the non-root bits BorrowFlag((self.0 & !ROOT) | (rooted as usize)) } } /// A mutable memory location with dynamically checked borrow rules /// that can be used inside of a garbage-collected pointer. /// /// This object is a `RefCell` that can be used inside of a `Gc<T>`. pub struct GcCell<T: ?Sized + 'static> { flags: Cell<BorrowFlag>, cell: UnsafeCell<T>, } impl<T: Trace> GcCell<T> { /// Creates a new `GcCell` containing `value`. #[inline] pub fn new(value: T) -> Self { GcCell { flags: Cell::new(BORROWFLAG_INIT), cell: UnsafeCell::new(value), } } /// Consumes the `GcCell`, returning the wrapped value. #[inline] pub fn into_inner(self) -> T { self.cell.into_inner() } } impl<T: Trace + ?Sized> GcCell<T> { /// Immutably borrows the wrapped value. /// /// The borrow lasts until the returned `GcCellRef` exits scope. /// Multiple immutable borrows can be taken out at the same time. /// /// # Panics /// /// Panics if the value is currently mutably borrowed. #[inline] pub fn borrow(&self) -> GcCellRef<'_, T> { match self.try_borrow() { Ok(value) => value, Err(e) => panic!("{}", e), } } /// Mutably borrows the wrapped value. /// /// The borrow lasts until the returned `GcCellRefMut` exits scope. /// The value cannot be borrowed while this borrow is active. /// /// # Panics /// /// Panics if the value is currently borrowed. #[inline] pub fn borrow_mut(&self) -> GcCellRefMut<'_, T> { match self.try_borrow_mut() { Ok(value) => value, Err(e) => panic!("{}", e), } } /// Immutably borrows the wrapped value, returning an error if the value is currently mutably /// borrowed. /// /// The borrow lasts until the returned `GcCellRef` exits scope. Multiple immutable borrows can be /// taken out at the same time. /// /// This is the non-panicking variant of [`borrow`](#method.borrow). /// /// # Examples /// /// ``` /// use gc::GcCell; /// /// let c = GcCell::new(5); /// /// { /// let m = c.borrow_mut(); /// assert!(c.try_borrow().is_err()); /// } /// /// { /// let m = c.borrow(); /// assert!(c.try_borrow().is_ok()); /// } /// ``` pub fn try_borrow(&self) -> Result<GcCellRef<'_, T>, BorrowError> { if self.flags.get().borrowed() == BorrowState::Writing { return Err(BorrowError); } self.flags.set(self.flags.get().add_reading()); // This will fail if the borrow count overflows, which shouldn't happen, // but let's be safe assert!(self.flags.get().borrowed() == BorrowState::Reading); unsafe { Ok(GcCellRef { flags: &self.flags, value: &*self.cell.get(), }) } } /// Mutably borrows the wrapped value, returning an error if the value is currently borrowed. /// /// The borrow lasts until the returned `GcCellRefMut` exits scope. /// The value cannot be borrowed while this borrow is active. /// /// This is the non-panicking variant of [`borrow_mut`](#method.borrow_mut). /// /// # Examples /// /// ``` /// use gc::GcCell; /// /// let c = GcCell::new(5); /// /// { /// let m = c.borrow(); /// assert!(c.try_borrow_mut().is_err()); /// } /// /// assert!(c.try_borrow_mut().is_ok()); /// ``` pub fn try_borrow_mut(&self) -> Result<GcCellRefMut<'_, T>, BorrowMutError> { if self.flags.get().borrowed() != BorrowState::Unused { return Err(BorrowMutError); } self.flags.set(self.flags.get().set_writing()); unsafe { // Force the val_ref's contents to be rooted for the duration of the // mutable borrow if !self.flags.get().rooted() { (*self.cell.get()).root(); } Ok(GcCellRefMut { gc_cell: self, value: &mut *self.cell.get(), }) } } } /// An error returned by [`GcCell::try_borrow`](struct.GcCell.html#method.try_borrow). #[derive(Debug, Clone, Copy, Eq, PartialEq, Ord, PartialOrd, Default, Hash)] pub struct BorrowError; impl std::fmt::Display for BorrowError { fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result { Display::fmt("GcCell<T> already mutably borrowed", f) } } /// An error returned by [`GcCell::try_borrow_mut`](struct.GcCell.html#method.try_borrow_mut). #[derive(Debug, Clone, Copy, Eq, PartialEq, Ord, PartialOrd, Default, Hash)] pub struct BorrowMutError; impl std::fmt::Display for BorrowMutError { fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result { Display::fmt("GcCell<T> already borrowed", f) } } impl<T: Trace + ?Sized> Finalize for GcCell<T> {} unsafe impl<T: Trace + ?Sized> Trace for GcCell<T> { #[inline] unsafe fn trace(&self) { match self.flags.get().borrowed() { BorrowState::Writing => (), _ => (*self.cell.get()).trace(), } } #[inline] unsafe fn root(&self) { assert!(!self.flags.get().rooted(), "Can't root a GcCell twice!"); self.flags.set(self.flags.get().set_rooted(true)); match self.flags.get().borrowed() { BorrowState::Writing => (), _ => (*self.cell.get()).root(), } } #[inline] unsafe fn unroot(&self) { assert!(self.flags.get().rooted(), "Can't unroot a GcCell twice!"); self.flags.set(self.flags.get().set_rooted(false)); match self.flags.get().borrowed() { BorrowState::Writing => (), _ => (*self.cell.get()).unroot(), } } #[inline] fn finalize_glue(&self) { Finalize::finalize(self); match self.flags.get().borrowed() { BorrowState::Writing => (), _ => unsafe { (*self.cell.get()).finalize_glue() }, } } } /// A wrapper type for an immutably borrowed value from a `GcCell<T>`. pub struct GcCellRef<'a, T: ?Sized + 'static> { flags: &'a Cell<BorrowFlag>, value: &'a T, } impl<'a, T: ?Sized> GcCellRef<'a, T> { /// Copies a `GcCellRef`. /// /// The `GcCell` is already immutably borrowed, so this cannot fail. /// /// This is an associated function that needs to be used as /// `GcCellRef::clone(...)`. A `Clone` implementation or a method /// would interfere with the use of `c.borrow().clone()` to clone /// the contents of a `GcCell`. #[inline] pub fn clone(orig: &GcCellRef<'a, T>) -> GcCellRef<'a, T> { orig.flags.set(orig.flags.get().add_reading()); GcCellRef { flags: orig.flags, value: orig.value, } } /// Makes a new `GcCellRef` from a component of the borrowed data. /// /// The `GcCell` is already immutably borrowed, so this cannot fail. /// /// This is an associated function that needs to be used as `GcCellRef::map(...)`. /// A method would interfere with methods of the same name on the contents /// of a `GcCellRef` used through `Deref`. /// /// # Examples /// /// ``` /// use gc::{GcCell, GcCellRef}; /// /// let c = GcCell::new((5, 'b')); /// let b1: GcCellRef<(u32, char)> = c.borrow(); /// let b2: GcCellRef<u32> = GcCellRef::map(b1, |t| &t.0); /// //assert_eq!(b2, 5); /// ``` #[inline] pub fn map<U, F>(orig: Self, f: F) -> GcCellRef<'a, U> where U: ?Sized, F: FnOnce(&T) -> &U, { let ret = GcCellRef { flags: orig.flags, value: f(orig.value), }; // We have to tell the compiler not to call the destructor of GcCellRef, // because it will update the borrow flags. std::mem::forget(orig); ret } /// Splits a `GcCellRef` into multiple `GcCellRef`s for different components of the borrowed data. /// /// The `GcCell` is already immutably borrowed, so this cannot fail. /// /// This is an associated function that needs to be used as GcCellRef::map_split(...). /// A method would interfere with methods of the same name on the contents of a `GcCellRef` used through `Deref`. /// /// # Examples /// /// ``` /// use gc::{GcCell, GcCellRef}; /// /// let cell = GcCell::new((1, 'c')); /// let borrow = cell.borrow(); /// let (first, second) = GcCellRef::map_split(borrow, |x| (&x.0, &x.1)); /// assert_eq!(*first, 1); /// assert_eq!(*second, 'c'); /// ``` #[inline] pub fn map_split<U, V, F>(orig: Self, f: F) -> (GcCellRef<'a, U>, GcCellRef<'a, V>) where U: ?Sized, V: ?Sized, F: FnOnce(&T) -> (&U, &V), { let (a, b) = f(orig.value); orig.flags.set(orig.flags.get().add_reading()); let ret = ( GcCellRef { flags: orig.flags, value: a, }, GcCellRef { flags: orig.flags, value: b, }, ); // We have to tell the compiler not to call the destructor of GcCellRef, // because it will update the borrow flags. std::mem::forget(orig); ret } } impl<'a, T: ?Sized> Deref for GcCellRef<'a, T> { type Target = T; #[inline] fn deref(&self) -> &T { self.value } } impl<'a, T: ?Sized> Drop for GcCellRef<'a, T> { fn drop(&mut self) { debug_assert!(self.flags.get().borrowed() == BorrowState::Reading); self.flags.set(self.flags.get().sub_reading()); } } impl<'a, T: ?Sized + Debug> Debug for GcCellRef<'a, T> { fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result { Debug::fmt(&**self, f) } } impl<'a, T: ?Sized + Display> Display for GcCellRef<'a, T> { fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result { Display::fmt(&**self, f) } } /// A wrapper type for a mutably borrowed value from a `GcCell<T>`. pub struct GcCellRefMut<'a, T: Trace + ?Sized + 'static, U: ?Sized = T> { gc_cell: &'a GcCell<T>, value: &'a mut U, } impl<'a, T: Trace + ?Sized, U: ?Sized> GcCellRefMut<'a, T, U> { /// Makes a new `GcCellRefMut` for a component of the borrowed data, e.g., an enum /// variant. /// /// The `GcCellRefMut` is already mutably borrowed, so this cannot fail. /// /// This is an associated function that needs to be used as /// `GcCellRefMut::map(...)`. A method would interfere with methods of the same /// name on the contents of a `GcCell` used through `Deref`. /// /// # Examples /// /// ``` /// use gc::{GcCell, GcCellRefMut}; /// /// let c = GcCell::new((5, 'b')); /// { /// let b1: GcCellRefMut<(u32, char)> = c.borrow_mut(); /// let mut b2: GcCellRefMut<(u32, char), u32> = GcCellRefMut::map(b1, |t| &mut t.0); /// assert_eq!(*b2, 5); /// *b2 = 42; /// } /// assert_eq!(*c.borrow(), (42, 'b')); /// ``` #[inline] pub fn map<V, F>(orig: Self, f: F) -> GcCellRefMut<'a, T, V> where V: ?Sized, F: FnOnce(&mut U) -> &mut V, { let value = unsafe { &mut *(orig.value as *mut U) }; let ret = GcCellRefMut { gc_cell: orig.gc_cell, value: f(value), }; // We have to tell the compiler not to call the destructor of GcCellRefMut, // because it will update the borrow flags. std::mem::forget(orig); ret } } impl<'a, T: Trace + ?Sized, U: ?Sized> Deref for GcCellRefMut<'a, T, U> { type Target = U; #[inline] fn deref(&self) -> &U { self.value } } impl<'a, T: Trace + ?Sized, U: ?Sized> DerefMut for GcCellRefMut<'a, T, U> { #[inline] fn deref_mut(&mut self) -> &mut U { self.value } } impl<'a, T: Trace + ?Sized, U: ?Sized> Drop for GcCellRefMut<'a, T, U> { #[inline] fn drop(&mut self) { debug_assert!(self.gc_cell.flags.get().borrowed() == BorrowState::Writing); // Restore the rooted state of the GcCell's contents to the state of the GcCell. // During the lifetime of the GcCellRefMut, the GcCell's contents are rooted. if !self.gc_cell.flags.get().rooted() { unsafe { (*self.gc_cell.cell.get()).unroot(); } } self.gc_cell .flags .set(self.gc_cell.flags.get().set_unused()); } } impl<'a, T: Trace + ?Sized, U: Debug + ?Sized> Debug for GcCellRefMut<'a, T, U> { fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result { Debug::fmt(&*(self.deref()), f) } } impl<'a, T: Trace + ?Sized, U: Display + ?Sized> Display for GcCellRefMut<'a, T, U> { fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result { Display::fmt(&**self, f) } } unsafe impl<T: ?Sized + Send> Send for GcCell<T> {} impl<T: Trace + Clone> Clone for GcCell<T> { #[inline] fn clone(&self) -> Self { Self::new(self.borrow().clone()) } } impl<T: Trace + Default> Default for GcCell<T> { #[inline] fn default() -> Self { Self::new(Default::default()) } } impl<T: Trace + ?Sized + PartialEq> PartialEq for GcCell<T> { #[inline(always)] fn eq(&self, other: &Self) -> bool { *self.borrow() == *other.borrow() } } impl<T: Trace + ?Sized + Eq> Eq for GcCell<T> {} impl<T: Trace + ?Sized + PartialOrd> PartialOrd for GcCell<T> { #[inline(always)] fn partial_cmp(&self, other: &Self) -> Option<Ordering> { (*self.borrow()).partial_cmp(&*other.borrow()) } #[inline(always)] fn lt(&self, other: &Self) -> bool { *self.borrow() < *other.borrow() } #[inline(always)] fn le(&self, other: &Self) -> bool { *self.borrow() <= *other.borrow() } #[inline(always)] fn gt(&self, other: &Self) -> bool { *self.borrow() > *other.borrow() } #[inline(always)] fn ge(&self, other: &Self) -> bool { *self.borrow() >= *other.borrow() } } impl<T: Trace + ?Sized + Ord> Ord for GcCell<T> { #[inline] fn cmp(&self, other: &GcCell<T>) -> Ordering { (*self.borrow()).cmp(&*other.borrow()) } } impl<T: Trace + ?Sized + Debug> Debug for GcCell<T> { fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result { match self.flags.get().borrowed() { BorrowState::Unused | BorrowState::Reading => f .debug_struct("GcCell") .field("value", &self.borrow()) .finish(), BorrowState::Writing => f .debug_struct("GcCell") .field("value", &"<borrowed>") .finish(), } } } // Sets the data pointer of a `?Sized` raw pointer. // // For a slice/trait object, this sets the `data` field and leaves the rest // unchanged. For a sized raw pointer, this simply sets the pointer. unsafe fn set_data_ptr<T: ?Sized, U>(mut ptr: *mut T, data: *mut U) -> *mut T { ptr::write(&mut ptr as *mut _ as *mut *mut u8, data as *mut u8); ptr }