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//! Single-threaded reference-counting persistent pointers use std::panic::RefUnwindSafe; use std::panic::UnwindSafe; use crate::alloc::{MemPool, PmemUsage}; use crate::cell::VCell; use crate::clone::*; use crate::ptr::Ptr; use crate::stm::*; use crate::*; use std::cmp::Ordering; use std::hash::Hash; use std::hash::Hasher; use std::marker::PhantomData; use std::mem::MaybeUninit; use std::ops::Deref; use std::*; #[derive(Debug)] struct Counter { strong: usize, weak: usize, #[cfg(not(feature = "no_log_rc"))] has_log: u8, } pub struct PrcBox<T: ?Sized, A: MemPool> { counter: Counter, #[cfg(not(feature = "no_volatile_pointers"))] vlist: VCell<VWeakList, A>, dummy: [A; 0], value: T, } unsafe impl<T: ?Sized, A: MemPool> PSafe for PrcBox<T, A> {} unsafe impl<T: ?Sized, A: MemPool> TxInSafe for PrcBox<T, A> {} impl<T: ?Sized, A: MemPool> UnwindSafe for PrcBox<T, A> {} impl<T: ?Sized, A: MemPool> RefUnwindSafe for PrcBox<T, A> {} impl<T: ?Sized, A: MemPool> !VSafe for PrcBox<T, A> {} unsafe fn set_data_ptr<T: ?Sized, U>(mut ptr: *mut T, data: *mut U) -> *mut T { std::ptr::write(&mut ptr as *mut _ as *mut *mut u8, data as *mut u8); ptr } /// A single-thread reference-counting persistent pointer. 'Prc' stands for /// 'Persistent Reference Counted'. /// /// The main aspect of `Prc<T>` is that its counters are transactional which /// means that functions [`pclone`], [`downgrade`], and [`upgrade`] require a /// [`Journal`] to operate. In other words, you need to wrap them in a /// [`transaction`]. /// /// `Prc` uses reference counting to manage memory. Although it provides a fast /// solution for deallocation without scan, cyclic references yield a memory /// leak. At this point, we have not provided a static solution to detect cyclic /// references. However, following Rust's partial solution for that, you may use /// [`Weak`] references for reference cycles. /// /// References to data can be strong (using [`pclone`]), weak (using [`downgrade`]), /// or volatile weak (using [`volatile`]). The first two generate NV-to-NV /// pointers, while the last on is a V-to-NV pointer. Please see [`Weak`] and /// [`VWeak`] for more details on their implementation and safety. /// /// # Examples /// /// ``` /// # use crndm::alloc::*; /// # type P = Heap; /// use crndm::prc::Prc; /// use crndm::clone::PClone; /// /// # #[allow(unused)] /// P::transaction(|j| { /// let p = Prc::<i32,P>::new(1, j); /// /// // Create a new persistent strong reference /// let s = p.pclone(j); /// /// assert_eq!(*p, *s); /// assert_eq!(2, Prc::strong_count(&p)); /// assert_eq!(0, Prc::weak_count(&p)); /// /// // Create a new persistent weak reference /// let w = Prc::downgrade(&p, j); /// assert_eq!(2, Prc::strong_count(&p)); /// assert_eq!(1, Prc::weak_count(&p)); /// /// // Create a new volatile weak reference /// let v = Prc::volatile(&p); /// assert_eq!(2, Prc::strong_count(&p)); /// assert_eq!(1, Prc::weak_count(&p)); /// /// // Upgrade the persistent weak ref to a strong ref /// let ws = w.upgrade(j).unwrap(); /// assert_eq!(3, Prc::strong_count(&p)); /// assert_eq!(1, Prc::weak_count(&p)); /// /// // Upgrade the volatile weak ref to a strong ref /// let vs = w.upgrade(j).unwrap(); /// assert_eq!(4, Prc::strong_count(&p)); /// assert_eq!(1, Prc::weak_count(&p)); /// }).unwrap(); /// ``` /// /// [`pclone`]: #method.pclone /// [`downgrade`]: #method.downgrade /// [`volatile`]: #method.volatile /// [`upgrade`]: ./struct.Weak.html#method.upgrade /// [`Journal`]: ../stm/journal/struct.Journal.html /// [`transaction`]: ../stm/fn.transaction.html pub struct Prc<T: PSafe + ?Sized, A: MemPool> { ptr: Ptr<PrcBox<T, A>, A>, phantom: PhantomData<T>, } impl<T: ?Sized, A: MemPool> !TxOutSafe for Prc<T, A> {} impl<T: ?Sized, A: MemPool> !Send for Prc<T, A> {} impl<T: ?Sized, A: MemPool> !Sync for Prc<T, A> {} impl<T: ?Sized, A: MemPool> !VSafe for Prc<T, A> {} impl<T: PSafe, A: MemPool> Prc<T, A> { /// Constructs a new `Prc<T>`. /// /// It also creates a `DropOnFailure` log to make sure that if the program /// crashes, the allocation drops of recovery. /// /// # Examples /// /// ``` /// # use crndm::alloc::*; /// # type P = Heap; /// use crndm::prc::Prc; /// /// P::transaction(|j| { /// let five = Prc::new(5, j); /// }).unwrap(); /// ``` pub fn new(value: T, journal: &Journal<A>) -> Prc<T, A> { unsafe { let ptr = Ptr::new_unchecked(A::new( PrcBox::<T, A> { counter: Counter { strong: 1, weak: 1, #[cfg(not(feature = "no_log_rc"))] has_log: 0, }, #[cfg(not(feature = "no_volatile_pointers"))] vlist: VCell::new(VWeakList::default()), dummy: [], value, }, journal, )); Self::from_inner(ptr) } } /// Constructs a new `Prc` with uninitialized contents. /// /// A `DropOnFailure` log is taken for the allocation. /// /// # Examples /// /// ``` /// # use crndm::alloc::*; /// # type P = Heap; /// use crndm::prc::Prc; /// /// P::transaction(|j| { /// let mut five = Prc::<u32,Heap>::new_uninit(j); /// /// let five = unsafe { /// // Deferred initialization: /// Prc::get_mut_unchecked(&mut five).as_mut_ptr().write(5); /// /// five.assume_init() /// }; /// /// assert_eq!(*five, 5) /// }).unwrap(); /// ``` pub fn new_uninit(journal: &Journal<A>) -> Prc<MaybeUninit<T>, A> { unsafe { Prc::from_inner(Ptr::from_mut(A::new( PrcBox { counter: Counter { strong: 1, weak: 1, #[cfg(not(feature = "no_log_rc"))] has_log: 0, }, #[cfg(not(feature = "no_volatile_pointers"))] vlist: VCell::new(VWeakList::default()), dummy: [], value: MaybeUninit::<T>::uninit(), }, journal, ))) } } /// Constructs a new `Prc` with uninitialized contents, with the memory /// being filled with `0` bytes. /// /// See `MaybeUninit::zeroed` for examples of correct and incorrect usage of /// this method. /// /// # Examples /// /// ``` /// # use crndm::alloc::*; /// # type P = Heap; /// use crndm::prc::Prc; /// /// P::transaction(|j| { /// let zero = Prc::<i32,P>::new_zeroed(j); /// let zero = unsafe { zero.assume_init() }; /// /// assert_eq!(*zero, 0) /// }).unwrap(); /// ``` /// pub fn new_zeroed(journal: &Journal<A>) -> Prc<mem::MaybeUninit<T>, A> { unsafe { let mut uninit = Self::new_uninit(journal); std::ptr::write_bytes::<T>(Prc::get_mut_unchecked(&mut uninit).as_mut_ptr(), 0, 1); uninit } } /// Owns contents of `p` without cloning, leaving `p` untouched pub fn from(p: Prc<T, A>) -> Self { let res = Self::from_inner(p.ptr); mem::forget(p); res } } impl<T: PSafe + ?Sized, A: MemPool> Prc<T, A> { #[inline] fn from_inner(ptr: Ptr<PrcBox<T, A>, A>) -> Self { Prc { ptr, phantom: PhantomData, } } #[inline(always)] fn inner(&self) -> &PrcBox<T, A> { self.ptr.as_ref() } #[allow(clippy::missing_safety_doc)] unsafe fn from_ptr(ptr: *mut PrcBox<T, A>, j: &Journal<A>) -> Self { let off = A::off_unchecked(ptr); let res = Self::from_inner(Ptr::from_off_unchecked(off)); res.inc_strong(j); res } } impl<T: PSafe, A: MemPool> Prc<mem::MaybeUninit<T>, A> { /// Converts to `Rc<T>`. /// /// # Safety /// /// As with [`MaybeUninit::assume_init`], /// it is up to the caller to guarantee that the inner value /// really is in an initialized state. /// Calling this when the content is not yet fully initialized /// causes immediate undefined behavior. /// /// [`MaybeUninit::assume_init`]: ../../std/mem/union.MaybeUninit.html#method.assume_init /// /// # Examples /// /// ``` /// # use crndm::alloc::*; /// # type P = Heap; /// use crndm::prc::Prc; /// /// crndm::transaction(|j| { /// let mut five = Prc::<u32,P>::new_uninit(j); /// /// let five = unsafe { /// // Deferred initialization: /// Prc::get_mut_unchecked(&mut five).as_mut_ptr().write(5); /// /// five.assume_init() /// }; /// /// assert_eq!(*five, 5); /// }).unwrap(); /// ``` #[inline] pub unsafe fn assume_init(self) -> Prc<T, A> { Prc::from_inner(mem::ManuallyDrop::new(self).ptr.cast()) } } impl<T: PSafe, A: MemPool> Prc<MaybeUninit<T>, A> { #[inline] /// Returns a mutable reference into the given `Prc`, if there are /// no other `Prc` or `Weak` pointers to the same allocation. /// /// Returns `None` otherwise, because it is not safe to mutate a shared /// value. It only works for `Prc<MaybeUninit<T>>` to be able to defer the /// initialization. /// /// # Examples /// /// ``` /// # use crndm::alloc::*; /// # type P = Heap; /// use crndm::prc::Prc; /// /// P::transaction(|j| { /// let mut five = Prc::<u32,P>::new_uninit(j); /// /// let five = unsafe { /// // Deferred initialization: /// Prc::get_mut(&mut five).unwrap().as_mut_ptr().write(5); /// /// five.assume_init() /// }; /// /// assert_eq!(*five, 5) /// }).unwrap(); /// ``` pub fn get_mut(this: &mut Self) -> Option<&mut MaybeUninit<T>> { if Prc::is_unique(this) { unsafe { Some(Prc::get_mut_unchecked(this)) } } else { None } } #[inline] /// Returns a mutable reference into the given `Prc`, /// without any check. /// /// It only works for `Prc<MaybeUninit<T>>` to be able to defer the /// initialization. /// /// # Safety /// /// Any other `Prc` or `Weak` pointers to the same allocation must not be /// dereferenced for the duration of the returned borrow. /// This is trivially the case if no such pointers exist, /// for example immediately after `Rc::new`. /// /// # Examples /// /// ``` /// # use crndm::alloc::*; /// # type P = Heap; /// use crndm::prc::Prc; /// /// P::transaction(|j| { /// let mut five = Prc::<i32,P>::new_uninit(j); /// /// let five = unsafe { /// // Deferred initialization: /// Prc::get_mut_unchecked(&mut five).as_mut_ptr().write(5); /// /// five.assume_init() /// }; /// /// assert_eq!(*five, 5); /// }).unwrap(); /// ``` pub unsafe fn get_mut_unchecked(this: &mut Self) -> &mut MaybeUninit<T> { &mut this.ptr.value } } impl<T: PSafe + ?Sized, A: MemPool> Prc<T, A> { /// Creates a new `Weak` pointer to this allocation. /// /// # Examples /// /// ``` /// # use crndm::alloc::*; /// # type P = Heap; /// use crndm::prc::Prc; /// /// P::transaction(|j| { /// let five = Prc::new(5, j); /// let _weak_five = Prc::downgrade(&five, j); /// }).unwrap() /// ``` pub fn downgrade(this: &Self, journal: &Journal<A>) -> Weak<T, A> { this.inc_weak(journal); debug_assert!(!this.ptr.is_dangling()); Weak { ptr: this.ptr } } /// Creates a new `VWeak` pointer to this allocation. pub fn volatile(this: &Self) -> VWeak<T, A> { debug_assert!(!this.ptr.is_dangling()); VWeak::new(this) } #[inline] /// Gets the number of `Weak` pointers to this allocation. /// /// # Examples /// /// ``` /// # use crndm::alloc::*; /// # type P = Heap; /// use crndm::prc::Prc; /// /// P::transaction(|j| { /// let five = Prc::new(5, j); /// /// let _weak_five = Prc::downgrade(&five, j); /// assert_eq!(1, Prc::weak_count(&five)); /// }).unwrap() /// ``` pub fn weak_count(this: &Self) -> usize { this.weak() - 1 } #[inline] /// Gets the number of `Weak` pointers to this allocation. /// /// # Examples /// /// ``` /// # use crndm::alloc::*; /// # type P = Heap; /// use crndm::prc::Prc; /// use crndm::clone::PClone; /// /// P::transaction(|j| { /// let five = Prc::new(5, j); /// let _also_five = Prc::pclone(&five, j); /// assert_eq!(2, Prc::strong_count(&five)); /// }).unwrap(); /// ``` pub fn strong_count(this: &Self) -> usize { this.strong() } #[inline] fn is_unique(this: &Self) -> bool { Prc::weak_count(this) == 0 && Prc::strong_count(this) == 1 } #[inline] /// Returns `true` if the two `Prc`s point to the same allocation /// (in a vein similar to [`ptr::eq`]). /// /// # Examples /// /// ``` /// # use crndm::alloc::*; /// # type P = Heap; /// use crndm::prc::Prc; /// use crndm::clone::PClone; /// /// P::transaction(|j| { /// let five = Prc::new(5, j); /// let same_five = Prc::pclone(&five, j); /// let other_five = Prc::new(5, j); /// /// assert!(Prc::ptr_eq(&five, &same_five)); /// assert!(!Prc::ptr_eq(&five, &other_five)); /// }).unwrap(); /// ``` /// /// [`ptr::eq`]: std::ptr::eq pub fn ptr_eq(this: &Self, other: &Self) -> bool { this.ptr.off() == other.ptr.off() } } impl<T: PSafe, A: MemPool> PmemUsage for Prc<T, A> { default fn size_of() -> usize { Ptr::<PrcBox<T, A>, A>::size_of() } } impl<T: PSafe + PmemUsage + ?Sized, A: MemPool> PmemUsage for Prc<T, A> { fn size_of() -> usize { Ptr::<PrcBox<T, A>, A>::size_of() + T::size_of() } } impl<T: PSafe + ?Sized, A: MemPool> Deref for Prc<T, A> { type Target = T; #[inline(always)] fn deref(&self) -> &T { &self.inner().value } } unsafe impl<#[may_dangle] T: PSafe + ?Sized, A: MemPool> Drop for Prc<T, A> { /// Drops the `Prc` safely /// /// This will decrement the strong reference count. If the strong reference /// count reaches zero then the only other references (if any) are /// `Weak`, so we `drop` the inner value on commit using a `DropOnCommit` log. /// /// # Examples /// /// ``` /// # use crndm::alloc::*; /// # type P = Heap; /// use crndm::prc::Prc; /// use crndm::clone::PClone; /// /// struct Foo; /// /// impl Drop for Foo { /// fn drop(&mut self) { /// println!("dropped!"); /// } /// } /// /// P::transaction(|j| { /// let foo = Prc::new(Foo, j); /// let foo2 = Prc::pclone(&foo, j); /// /// drop(foo); // Doesn't print anything /// drop(foo2); // Prints "dropped!" /// }).unwrap(); /// ``` /// fn drop(&mut self) { unsafe { let journal = Journal::<A>::current(true).unwrap(); self.dec_strong(journal.0); if self.strong() == 0 { // TODO: Add "or it is unreachable from the root" // destroy the contained object std::ptr::drop_in_place(&mut self.ptr.as_mut().value); self.dec_weak(journal.0); if self.weak() == 0 { A::free(self.ptr.as_mut()); #[cfg(not(feature = "no_volatile_pointers"))] std::ptr::drop_in_place(&mut self.ptr.as_mut().vlist); } } } } } impl<T: PSafe + ?Sized, A: MemPool> PClone<A> for Prc<T, A> { #[inline] /// Creates a new strong reference to the object /// /// It increments the strong reference counter in a failure-atomic manner. /// When a transaction is aborted or power fails, every strong references /// to the object should be gone, and the counters should rollback to the /// consistent state before the transaction. /// /// # Examples /// /// ``` /// # use crndm::default::*; /// # type P = BuddyAlloc; /// let root = P::open::<Prc<i32>>("foo.pool", O_CF).unwrap(); /// /// let _ = P::transaction(|j| { /// let _n1 = root.pclone(j); /// let _n2 = root.pclone(j); /// let _n3 = root.pclone(j); /// assert_eq!(4, Prc::strong_count(&root)); /// panic!("abort") /// }); /// /// assert_eq!(1, Prc::strong_count(&root)); /// ``` fn pclone(&self, journal: &Journal<A>) -> Prc<T, A> { self.inc_strong(journal); Self::from_inner(self.ptr) } } impl<T: RootObj<A> + PSafe, A: MemPool> RootObj<A> for Prc<T, A> { #[inline] default fn init(journal: &Journal<A>) -> Prc<T, A> { Prc::new(T::init(journal), journal) } } impl<T: Default + PSafe + ?Sized, A: MemPool> RootObj<A> for Prc<T, A> { #[inline] default fn init(journal: &Journal<A>) -> Prc<T, A> { Prc::new(T::default(), journal) } } trait RcEqIdent<T: PartialEq + PSafe + ?Sized, A: MemPool> { fn eq(&self, other: &Prc<T, A>) -> bool; fn ne(&self, other: &Prc<T, A>) -> bool; } impl<T: PartialEq + PSafe + ?Sized, A: MemPool> RcEqIdent<T, A> for Prc<T, A> { #[inline] fn eq(&self, other: &Prc<T, A>) -> bool { **self == **other } #[inline] fn ne(&self, other: &Prc<T, A>) -> bool { **self != **other } } impl<T: PartialEq + PSafe + ?Sized, A: MemPool> PartialEq for Prc<T, A> { #[inline] fn eq(&self, other: &Prc<T, A>) -> bool { RcEqIdent::eq(self, other) } } impl<T: Eq + PSafe + ?Sized, A: MemPool> Eq for Prc<T, A> {} impl<T: PartialOrd + PSafe + ?Sized, A: MemPool> PartialOrd for Prc<T, A> { #[inline(always)] fn partial_cmp(&self, other: &Prc<T, A>) -> Option<Ordering> { (**self).partial_cmp(&**other) } #[inline(always)] fn lt(&self, other: &Prc<T, A>) -> bool { **self < **other } #[inline(always)] fn le(&self, other: &Prc<T, A>) -> bool { **self <= **other } #[inline(always)] fn gt(&self, other: &Prc<T, A>) -> bool { **self > **other } #[inline(always)] fn ge(&self, other: &Prc<T, A>) -> bool { **self >= **other } } impl<T: Ord + PSafe + ?Sized, A: MemPool> Ord for Prc<T, A> { #[inline] fn cmp(&self, other: &Prc<T, A>) -> Ordering { (**self).cmp(&**other) } } impl<T: Hash + PSafe + ?Sized, A: MemPool> Hash for Prc<T, A> { fn hash<H: Hasher>(&self, state: &mut H) { (**self).hash(state); } } impl<T: fmt::Display + PSafe + ?Sized, A: MemPool> fmt::Display for Prc<T, A> { fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result { fmt::Display::fmt(&**self, f) } } impl<T: fmt::Debug + PSafe + ?Sized, A: MemPool> fmt::Debug for Prc<T, A> { fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result { self.deref().fmt(f) } } impl<T: PSafe + ?Sized, A: MemPool> fmt::Pointer for Prc<T, A> { fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result { fmt::Pointer::fmt(&(&**self as *const T), f) } } /// `Weak` is a version of [`Prc`] that holds a non-owning reference to the /// managed allocation. The allocation is accessed by calling [`upgrade`] on the `Weak` /// pointer, which returns an [`Option`]`<`[`Prc`]`<T>>`. /// /// Since a `Weak` reference does not count towards ownership, it will not /// prevent the value stored in the allocation from being dropped, and `Weak` itself makes no /// guarantees about the value still being present. Thus it may return [`None`] /// when [`upgrade`]d. Note however that a `Weak` reference *does* prevent the allocation /// itself (the backing store) from being deallocated. /// /// A `Weak` pointer is useful for keeping a temporary reference to the allocation /// managed by [`Prc`] without preventing its inner value from being dropped. It is also used to /// prevent circular references between [`Prc`] pointers, since mutual owning references /// would never allow either [`Prc`] to be dropped. For example, a tree could /// have strong [`Prc`] pointers from parent nodes to children, and `Weak` /// pointers from children back to their parents. /// /// The typical way to obtain a `Weak` pointer is to call [`Prc::downgrade`]. /// /// [`Prc`]: struct.Prc.html /// [`Prc::downgrade`]: ./struct.Prc.html#method.downgrade /// [`upgrade`]: #method.upgrade /// [`Option`]: std::option::Option /// [`None`]: std::option::Option::None pub struct Weak<T: PSafe + ?Sized, A: MemPool> { ptr: Ptr<PrcBox<T, A>, A>, } impl<T: ?Sized, A: MemPool> !TxOutSafe for Weak<T, A> {} impl<T: ?Sized, A: MemPool> !Send for Weak<T, A> {} impl<T: ?Sized, A: MemPool> !Sync for Weak<T, A> {} impl<T: ?Sized, A: MemPool> !VSafe for Weak<T, A> {} impl<T: PSafe, A: MemPool> Weak<T, A> { pub fn as_raw(&self) -> *const T { match self.inner() { None => std::ptr::null(), Some(inner) => { let offset = data_offset_sized::<T, A>(); let ptr = inner as *const PrcBox<T, A>; // Note: while the pointer we create may already point to dropped value, the // allocation still lives (it must hold the weak point as long as we are alive). // Therefore, the offset is OK to do, it won't get out of the allocation. let ptr = unsafe { (ptr as *const u8).offset(offset) }; ptr as *const T } } } pub fn into_raw(self) -> *const T { let result = self.as_raw(); mem::forget(self); result } #[allow(clippy::missing_safety_doc)] pub unsafe fn from_raw(ptr: *const T) -> Self { if ptr.is_null() { Self::new() } else { // See Rc::from_raw for details let offset = data_offset::<T, A>(ptr); let fake_ptr = ptr as *mut PrcBox<T, A>; let ptr = set_data_ptr(fake_ptr, (ptr as *mut u8).offset(-offset)); Weak { ptr: Ptr::from_raw(ptr), } } } } impl<T: PSafe + ?Sized, A: MemPool> Weak<T, A> { /// Creates a new dangling weak pointer pub fn new() -> Weak<T, A> { Weak { ptr: Ptr::dangling(), } } pub fn upgrade(&self, journal: &Journal<A>) -> Option<Prc<T, A>> { let inner = self.inner()?; if inner.strong() == 0 { None } else { inner.inc_strong(journal); Some(Prc::from_inner(self.ptr)) } } pub fn strong_count(&self) -> usize { if let Some(inner) = self.inner() { inner.strong() } else { 0 } } pub fn weak_count(&self) -> Option<usize> { self.inner().map(|inner| { if inner.strong() > 0 { inner.weak() - 1 // subtract the implicit weak ptr } else { inner.weak() } }) } #[inline] fn inner(&self) -> Option<&PrcBox<T, A>> { if self.ptr.is_dangling() { None } else { Some(self.ptr.get_mut()) } } #[inline] pub fn ptr_eq(&self, other: &Self) -> bool { self.ptr == other.ptr } } impl<T: PSafe + ?Sized, A: MemPool> Drop for Weak<T, A> { fn drop(&mut self) { if let Some(inner) = self.inner() { let journal = Journal::<A>::current(true).unwrap(); inner.dec_weak(journal.0); if inner.weak() == 0 { unsafe { A::free(self.ptr.as_mut()); #[cfg(not(feature = "no_volatile_pointers"))] std::ptr::drop_in_place(&mut self.ptr.as_mut().vlist); } } } } } impl<T: PSafe + ?Sized, A: MemPool> PClone<A> for Weak<T, A> { #[inline] fn pclone(&self, journal: &Journal<A>) -> Weak<T, A> { if let Some(inner) = self.inner() { inner.inc_weak(journal) } Weak { ptr: self.ptr } } } impl<T: PSafe + fmt::Debug + ?Sized, A: MemPool> fmt::Debug for Weak<T, A> { fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result { write!(f, "(Weak)") } } impl<T: PSafe + ?Sized, A: MemPool> RootObj<A> for Weak<T, A> { fn init(_: &Journal<A>) -> Weak<T, A> { Weak::new() } } trait PrcBoxPtr<T: PSafe + ?Sized, A: MemPool> { #[allow(clippy::mut_from_ref)] fn count(&self) -> &mut Counter; #[inline] fn strong(&self) -> usize { self.count().strong } #[inline] #[cfg(not(feature = "no_log_rc"))] fn log_count(&self, journal: &Journal<A>) { let inner = self.count(); if inner.has_log == 0 { unsafe { inner.take_log(journal, Notifier::NonAtomic(Ptr::from_ref(&inner.has_log))); } } } #[inline] fn inc_strong(&self, _journal: &Journal<A>) { let inner = self.count(); let strong = inner.strong; if strong == 0 || strong == usize::max_value() { std::process::abort(); } #[cfg(not(feature = "no_log_rc"))] self.log_count(_journal); inner.strong += 1; } #[inline] fn dec_strong(&self, _journal: &Journal<A>) { #[cfg(not(feature = "no_log_rc"))] self.log_count(_journal); self.count().strong -= 1; } #[inline] fn weak(&self) -> usize { self.count().weak } #[inline] fn inc_weak(&self, _journal: &Journal<A>) { let weak = self.weak(); if weak == 0 || weak == usize::max_value() { std::process::abort(); } #[cfg(not(feature = "no_log_rc"))] self.log_count(_journal); self.count().weak += 1; } #[inline] fn dec_weak(&self, _journal: &Journal<A>) { #[cfg(not(feature = "no_log_rc"))] self.log_count(_journal); self.count().weak -= 1; } } impl<T: PSafe + ?Sized, A: MemPool> PrcBoxPtr<T, A> for Prc<T, A> { #[inline(always)] fn count(&self) -> &mut Counter { &mut self.ptr.get_mut().counter } } impl<T: PSafe + ?Sized, A: MemPool> PrcBoxPtr<T, A> for PrcBox<T, A> { #[inline(always)] fn count(&self) -> &mut Counter { unsafe { let ptr: *const Self = self; let ptr: *mut Self = ptr as *mut Self; let rcbox: &mut Self = &mut *ptr; &mut rcbox.counter } } } impl<T: PSafe + ?Sized, A: MemPool> borrow::Borrow<T> for Prc<T, A> { fn borrow(&self) -> &T { &self.inner().value } } impl<T: PSafe + ?Sized, A: MemPool> AsRef<T> for Prc<T, A> { fn as_ref(&self) -> &T { &self.inner().value } } impl<T: PSafe + ?Sized, A: MemPool> Unpin for Prc<T, A> {} unsafe fn data_offset<T: ?Sized, A: MemPool>(ptr: *const T) -> isize { data_offset_align::<A>(mem::align_of_val(&*ptr)) } fn data_offset_sized<T, A: MemPool>() -> isize { data_offset_align::<A>(mem::align_of::<T>()) } #[inline] fn data_offset_align<A: MemPool>(align: usize) -> isize { let layout = std::alloc::Layout::new::<PrcBox<(), A>>(); (layout.size() + layout.padding_needed_for(align)) as isize } pub fn ws<T: PSafe, A: MemPool>(ptr: &Prc<T, A>) -> (usize, usize) { let i = ptr.inner(); (i.strong(), i.weak()) } /// `VWeak` is a version of [`Prc`] that holds a non-owning reference to the /// managed allocation in the volatile heap. The allocation is accessed by /// calling [`upgrade`] on the `VWeak` pointer, which returns an /// [`Option`]`<`[`Prc`]`<T>>`. /// /// Since a `VWeak` reference does not count towards ownership, it will not /// prevent the value stored in the allocation from being dropped, and `VWeak` /// itself makes no guarantees about the value still being present. Thus it may /// return [`None`] when [`upgrade`]d. Note however that a `VWeak` reference, /// unlike [`Weak`], *does NOT* prevent the allocation itself (the backing /// store) from being deallocated. /// /// A `VWeak` pointer is useful for keeping a temporary reference to the /// persistent allocation managed by [`Prc`] without preventing its inner value /// from being dropped from ... It is also used to /// prevent circular references between [`Prc`] pointers, since mutual owning references /// would never allow either [`Prc`] to be dropped. For example, a tree could /// have strong [`Prc`] pointers from parent nodes to children, and `Weak` /// pointers from children back to their parents. /// /// The typical way to obtain a `VWeak` pointer is to call [`Prc::volatile`]. /// /// [`Prc`]: struct.Prc.html /// [`Weak`]: struct.Weak.html /// [`Prc::downgrade`]: ./struct.Prc.html#method.downgrade /// [`upgrade`]: #method.upgrade /// [`Option`]: std::option::Option /// [`None`]: std::option::Option::None pub struct VWeak<T: ?Sized, A: MemPool> { ptr: *const PrcBox<T, A>, valid: *mut VWeakValid, gen: u32, } impl<T: ?Sized, A: MemPool> !Send for VWeak<T, A> {} impl<T: ?Sized, A: MemPool> !Sync for VWeak<T, A> {} impl<T: ?Sized, A: MemPool> UnwindSafe for VWeak<T, A> {} impl<T: ?Sized, A: MemPool> RefUnwindSafe for VWeak<T, A> {} unsafe impl<T: ?Sized, A: MemPool> TxInSafe for VWeak<T, A> {} unsafe impl<T: ?Sized, A: MemPool> TxOutSafe for VWeak<T, A> {} unsafe impl<T: ?Sized, A: MemPool> PSafe for VWeak<T, A> {} impl<T: PSafe + ?Sized, A: MemPool> VWeak<T, A> { fn new(prc: &Prc<T, A>) -> VWeak<T, A> { let list = prc.ptr.vlist.as_mut(); VWeak { ptr: prc.ptr.as_ref(), valid: list.append(), gen: A::gen(), } } pub fn null() -> VWeak<T, A> where T: Sized { VWeak { ptr: std::ptr::null(), valid: std::ptr::null_mut(), gen: u32::MAX, } } pub fn upgrade(&self, journal: &Journal<A>) -> Option<Prc<T, A>> { let inner = self.inner()?; let strong = inner.counter.strong; if strong == 0 { None } else { unsafe { Some(Prc::from_ptr(self.ptr as *const _ as *mut _, journal)) } } } #[inline] fn inner(&self) -> Option<&PrcBox<T, A>> { unsafe { if self.gen != A::gen() { None } else if !(*self.valid).valid { None } else { Some(&*self.ptr) } } } } impl<T: PSafe + ?Sized, A: MemPool> Clone for VWeak<T, A> { fn clone(&self) -> Self { if self.gen == A::gen() { unsafe { if (*self.valid).valid { let list = (*self.ptr).vlist.as_mut(); return VWeak { ptr: self.ptr, valid: list.append(), gen: self.gen, }; } } } VWeak { ptr: self.ptr, valid: self.valid, gen: self.gen, } } } impl<T: ?Sized, A: MemPool> Drop for VWeak<T, A> { fn drop(&mut self) { unsafe { let this = &mut *self.valid; if self.gen == A::gen() { if !this.list.is_null() { let head = &mut (*this.list).head; if this.prev.is_null() { *head = this.next; } else { (*this.prev).next = this.next; } if !this.next.is_null() { (*this.next).prev = this.prev; } } } } } } struct VWeakValid { valid: bool, next: *mut VWeakValid, prev: *mut VWeakValid, list: *mut VWeakList, } struct VWeakList { head: *mut VWeakValid, } impl VWeakList { fn append(&mut self) -> *mut VWeakValid { let new = Box::into_raw(Box::new(VWeakValid { valid: true, next: self.head, prev: std::ptr::null_mut(), list: self as *mut Self, })); if !self.head.is_null() { unsafe { (*self.head).prev = new; } } self.head = new; new } } impl Default for VWeakList { fn default() -> Self { VWeakList { head: std::ptr::null_mut(), } } } impl Drop for VWeakList { fn drop(&mut self) { unsafe { let mut curr = self.head; while !curr.is_null() { (*curr).valid = false; (*curr).list = std::ptr::null_mut(); curr = (*curr).next; } } } }