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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::clone::Clone as StdClone; 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::sync::atomic::{self, AtomicBool, AtomicUsize, Ordering::*}; use std::*; const MAX_REFCOUNT: usize = (isize::MAX) as usize; #[derive(Debug)] struct Counter { strong: AtomicUsize, weak: AtomicUsize, #[cfg(not(feature = "no_log_rc"))] has_log: u8, } unsafe impl PSafe for Counter {} /// The [`Parc`]'s inner data type /// /// It contains the atomic counters, a list of volatile references, and the /// actual value. /// /// [`Parc`]: # pub struct ParcInner<T: ?Sized, A: MemPool> { counter: Counter, #[cfg(not(feature = "no_volatile_pointers"))] vlist: VCell<VWeakList, A>, marker: PhantomData<A>, value: T, } unsafe impl<T: PSafe + ?Sized, A: MemPool> PSafe for ParcInner<T, A> {} impl<T: ?Sized, A: MemPool> !VSafe for ParcInner<T, A> {} unsafe fn set_data_ptr<T, 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 thread-safe reference-counting persistent pointer. 'Parc' stands for /// 'Persistent Atomically Reference Counted'. /// /// The main aspect of `Parc<T>` is that its atomic counters are also /// transactional to provide failure atomicity which means that functions /// [`pclone`], [`downgrade`], and [`upgrade`] require a [`Journal`] to operate. /// In other words, you need to wrap them in a [`transaction`]. The counters are /// atomic, so it is safe to share it in multiple threads. /// /// Unlike [`Arc`], `Parc` does not implement [`Send`] to prevent memory leak. /// The reason is that if a `Parc` is created in a transaction without being /// reachable from the root object, and moves to a thread, due to being RAII, /// its drop function gets called in the other thread outside the original /// transaction. Therefore, it destroys allocation consistency and leaves the /// `Parc` unreachable in the memory if a crash happens between the original /// transaction is done and the drop function is called. /// /// To allow sharing, `Parc` provides a safe mechanism to cross the thread /// boundaries. When you need to share it, you can obtain a [`VWeak`] /// object by calling [`volatile()`] function. The [`VWeak`] object is both /// [`Sync`] and [`Send`] and acts like a volatile reference. Calling /// [`VWeak`]`::`[`upgrade()`] gives access to data by creating a new reference /// of type `Parc` inside the other thread, if the referent is still available. /// Calling [`volatile()`] is dynamically prohibited to be inside a transaction. /// Therefore, the `Parc` should be already reachable from the root object and /// packed outside a transaction. /// /// # Examples /// /// ``` /// use crndm::default::*; /// use std::thread; /// /// type P = BuddyAlloc; /// /// let p = P::open::<Parc<i32>>("foo.pool", O_CF).unwrap(); /// let v = p.volatile(); /// let mut threads = vec![]; /// /// for i in 0..10 { /// let p = v.clone(); /// threads.push(thread::spawn(move || { /// transaction(|j| { /// if let Some(p) = p.upgrade(j) { /// println!("access {} from thread {}", *p, i); /// } /// }).unwrap(); /// })); /// } /// /// for t in threads { /// t.join().unwrap(); /// } /// ``` /// /// # Mutability /// /// `Parc` doesn't provide mutable reference to the inner value. To allow /// interior mutability, you may use `Parc<`[`Mutex`]`<T,P>,P>` (or in short, /// `Parc<`[`PMutex`]`<T>>` using aliased types). /// /// ``` /// use crndm::default::*; /// use std::thread; /// /// type P = BuddyAlloc; /// /// let p = P::open::<Parc<PMutex<i32>>>("foo.pool", O_CF).unwrap(); /// let v = p.volatile(); /// let mut threads = vec![]; /// /// for i in 0..10 { /// let p = v.clone(); /// threads.push(thread::spawn(move || { /// transaction(|j| { /// if let Some(p) = p.upgrade(j) { /// let mut p = p.lock(j); /// *p += 1; /// println!("thread {} makes it {}", i, *p); /// } /// }).unwrap(); /// })); /// } /// /// for t in threads { /// t.join().unwrap(); /// } /// /// let res = transaction(|j| { /// *p.lock(j) /// }).unwrap(); /// /// assert_eq!(res, 10); /// ``` /// /// [`downgrade`]: #method.downgrade /// [`upgrade`]: ./struct.Weak.html#method.upgrade /// [`Journal`]: ../stm/journal/struct.Journal.html /// [`transaction`]: ../stm/fn.transaction.html /// [`Arc`]: std::sync::Arc /// [`Mutex`]: ./struct.Mutex.html /// [`PMutex`]: ../alloc/default/type.PMutex.html /// [`pclone`]: #impl-PClone /// [`volatile()`]: #method.volatile /// [`upgrade()`]: ./struct.VWeak.html#method.upgrade pub struct Parc<T: PSafe + ?Sized, A: MemPool> { ptr: Ptr<ParcInner<T, A>, A>, phantom: PhantomData<T>, } impl<T: ?Sized, A: MemPool> !TxOutSafe for Parc<T, A> {} impl<T: ?Sized, A: MemPool> !Send for Parc<T, A> {} impl<T: ?Sized, A: MemPool> !VSafe for Parc<T, A> {} impl<T: PSafe + ?Sized, A: MemPool> UnwindSafe for Parc<T, A> {} impl<T: PSafe + ?Sized, A: MemPool> RefUnwindSafe for Parc<T, A> {} unsafe impl<T: PSafe + ?Sized, A: MemPool> TxInSafe for Parc<T, A> {} impl<T: PSafe, A: MemPool> Parc<T, A> { /// Constructs a new `Parc<T>`. /// /// # Examples /// /// ``` /// # use crndm::alloc::*; /// use crndm::sync::Parc; /// /// Heap::transaction(|j| { /// let five = Parc::new(5, j); /// }).unwrap(); /// ``` pub fn new(value: T, journal: &Journal<A>) -> Parc<T, A> { unsafe { let ptr = Ptr::new_unchecked(A::new( ParcInner::<T, A> { counter: Counter { strong: AtomicUsize::new(1), weak: AtomicUsize::new(1), #[cfg(not(feature = "no_log_rc"))] has_log: 0, }, #[cfg(not(feature = "no_volatile_pointers"))] vlist: VCell::new(VWeakList::default()), marker: PhantomData, value, }, journal, )); Self::from_inner(ptr) } } /// Constructs a new `Parc` with uninitialized contents. /// /// # Examples /// /// ``` /// use crndm::alloc::*; /// use crndm::sync::Parc; /// /// crndm::transaction(|j| { /// let mut five = Parc::<u32,Heap>::new_uninit(j); /// /// let five = unsafe { /// // Deferred initialization: /// Parc::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>) -> Parc<MaybeUninit<T>, A> { unsafe { Parc::from_inner(Ptr::from_mut(A::new( ParcInner { counter: Counter { strong: AtomicUsize::new(1), weak: AtomicUsize::new(1), #[cfg(not(feature = "no_log_rc"))] has_log: 0, }, #[cfg(not(feature = "no_volatile_pointers"))] vlist: VCell::new(VWeakList::default()), marker: PhantomData, value: MaybeUninit::<T>::uninit(), }, journal, ))) } } /// Constructs a new `Parc` 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::*; /// use crndm::sync::Parc; /// /// Heap::transaction(|j| { /// let zero = Parc::<u32,Heap>::new_zeroed(j); /// let zero = unsafe { zero.assume_init() }; /// /// assert_eq!(*zero, 0) /// }).unwrap(); /// ``` /// pub fn new_zeroed(journal: &Journal<A>) -> Parc<mem::MaybeUninit<T>, A> { unsafe { let mut uninit = Self::new_uninit(journal); std::ptr::write_bytes::<T>(Parc::get_mut_unchecked(&mut uninit).as_mut_ptr(), 0, 1); uninit } } } impl<T: PSafe + ?Sized, A: MemPool> Parc<T, A> { #[inline] fn from_inner(ptr: Ptr<ParcInner<T, A>, A>) -> Self { Parc { ptr, phantom: PhantomData, } } #[inline(always)] fn inner(&self) -> &ParcInner<T, A> { self.ptr.as_ref() } #[allow(clippy::missing_safety_doc)] unsafe fn from_ptr(ptr: *mut ParcInner<T, A>, j: &Journal<A>) -> Self { let off = A::off_unchecked(ptr); let res = Self::from_inner(Ptr::from_off_unchecked(off)); #[cfg(not(feature = "no_log_rc"))] res.log_count(j); res.inner().counter.strong.fetch_add(1, Relaxed); res } #[inline(never)] unsafe fn drop_slow(&mut self) { // Destroy the data at this time, even though we may not free the box // allocation itself (there may still be weak pointers lying around). std::ptr::drop_in_place(&mut self.ptr.as_mut().value); if self.inner().counter.weak.fetch_sub(1, Release) == 1 { atomic::fence(Acquire); A::free(self.ptr.as_mut()); #[cfg(not(feature = "no_volatile_pointers"))] std::ptr::drop_in_place(self.ptr.as_mut().vlist.as_mut()); } } } impl<T: PSafe, A: MemPool> Parc<mem::MaybeUninit<T>, A> { /// Converts to `Parc<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::MaybeUninit#method.assume_init /// /// # Examples /// /// ``` /// use crndm::alloc::*; /// use crndm::sync::Parc; /// /// crndm::transaction(|j| { /// let mut five = Parc::<u32,Heap>::new_uninit(j); /// /// let five = unsafe { /// // Deferred initialization: /// Parc::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) -> Parc<T, A> { Parc::from_inner(mem::ManuallyDrop::new(self).ptr.cast()) } } impl<T: PSafe, A: MemPool> Parc<MaybeUninit<T>, A> { #[inline] /// Returns a mutable reference into the given `Parc`, if there are /// no other [`Parc`] or [`Weak`] pointers to the same allocation. /// /// Returns `None` otherwise, because it is not safe to mutate a shared /// value. It only works for `Parc<MaybeUninit<T>>` to be able to defer the /// initialization. /// /// # Examples /// /// ``` /// use crndm::alloc::*; /// use crndm::sync::Parc; /// /// crndm::transaction(|j| { /// let mut five = Parc::<u32,Heap>::new_uninit(j); /// /// let five = unsafe { /// // Deferred initialization: /// Parc::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 Parc::is_unique(this) { unsafe { Some(Parc::get_mut_unchecked(this)) } } else { None } } #[inline] /// Returns a mutable reference into the given `Parc`, without any check. /// /// It only works for `Parc<MaybeUninit<T>>` to be able to defer the /// initialization. /// /// # Safety /// /// Any other [`Parc`] 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 [`Parc::new`]. /// /// # Examples /// /// ``` /// use crndm::alloc::*; /// use crndm::sync::Parc; /// /// crndm::transaction(|j| { /// let mut five = Parc::<u32,Heap>::new_uninit(j); /// /// let five = unsafe { /// // Deferred initialization: /// Parc::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> Parc<T, A> { /// Creates a new [`Weak`] pointer to this allocation. /// /// The [`Weak`] pointer can be [`upgrade`]d later in a transaction. /// /// # Examples /// /// ``` /// use crndm::alloc::*; /// use crndm::sync::Parc; /// /// Heap::transaction(|j| { /// let five = Parc::new(5, j); /// let _weak_five = Parc::downgrade(&five, j); /// }).unwrap() /// ``` /// /// [`upgrade`]: ./struct.Weak.html#method.upgrade pub fn downgrade(this: &Self, _journal: &Journal<A>) -> Weak<T, A> { // This Relaxed is OK because we're checking the value in the CAS // below. let mut cur = this.inner().counter.weak.load(Relaxed); loop { // check if the weak counter is currently "locked"; if so, spin. if cur == usize::MAX { cur = this.inner().counter.weak.load(Relaxed); continue; } #[cfg(not(feature = "no_log_rc"))] this.log_count(_journal); // NOTE: this code currently ignores the possibility of overflow // into usize::MAX; in general both Rc and Arc need to be adjusted // to deal with overflow. // Unlike with Clone(), we need this to be an Acquire read to // synchronize with the write coming from `is_unique`, so that the // events prior to that write happen before this read. match this .inner() .counter .weak .compare_exchange_weak(cur, cur + 1, Acquire, Relaxed) { Ok(_) => { // Make sure we do not create a dangling Weak debug_assert!(!this.ptr.is_dangling()); return Weak { ptr: this.ptr.clone(), }; } Err(old) => cur = old, } } } /// Creates a new sharable [`VWeak`](./struct.VWeak.html) pointer to this /// allocation. /// /// # Errors /// /// This function requires the allocation to be reachable from the /// persistent root. Therefore, it panics if it gets called inside a /// transaction. /// /// # Examples /// /// ``` /// use crndm::default::*; /// /// type P = BuddyAlloc; /// /// let obj = P::open::<Parc<i32>>("foo.pool", O_CF).unwrap(); /// /// let v = obj.volatile(); /// assert_eq!(Parc::strong_count(&obj), 1); /// /// P::transaction(|j| { /// if let Some(obj) = v.upgrade(j) { /// assert_eq!(Parc::strong_count(&obj), 2); /// } /// }).unwrap(); /// /// assert_eq!(Parc::strong_count(&obj), 1); /// ``` pub fn volatile(&self) -> VWeak<T, A> { debug_assert!(!self.ptr.is_dangling()); assert!( Journal::<A>::try_current().is_none(), "Parc::volatile() cannot be used inside a transaction" ); VWeak::new(self) } #[inline] /// Gets the number of `Weak` pointers to this allocation. /// /// # Examples /// /// ``` /// use crndm::alloc::*; /// use crndm::sync::Parc; /// /// Heap::transaction(|j| { /// let five = Parc::new(5, j); /// /// let _weak_five = Parc::downgrade(&five, j); /// assert_eq!(1, Parc::weak_count(&five)); /// }).unwrap() /// ``` pub fn weak_count(this: &Self) -> usize { let cnt = this.inner().counter.weak.load(SeqCst); // If the weak count is currently locked, the value of the // count was 0 just before taking the lock. if cnt == usize::MAX { 0 } else { cnt - 1 } } #[inline] /// Gets the number of `Strong` pointers to this allocation. /// /// # Examples /// /// ``` /// use crndm::alloc::*; /// use crndm::sync::Parc; /// use crndm::clone::PClone; /// /// Heap::transaction(|j| { /// let five = Parc::new(5, j); /// let _also_five = Parc::pclone(&five, j); /// assert_eq!(2, Parc::strong_count(&five)); /// }).unwrap(); /// ``` pub fn strong_count(this: &Self) -> usize { this.inner().counter.strong.load(SeqCst) } #[inline] fn is_unique(this: &Self) -> bool { Parc::weak_count(this) == 0 && Parc::strong_count(this) == 1 } #[inline] /// Returns `true` if the two `Parc`s point to the same allocation /// (in a vein similar to [`std::ptr::eq`]). /// /// # Examples /// /// ``` /// use crndm::alloc::*; /// use crndm::sync::Parc; /// use crndm::clone::PClone; /// /// Heap::transaction(|j| { /// let five = Parc::new(5, j); /// let same_five = Parc::pclone(&five, j); /// let other_five = Parc::new(5, j); /// /// assert!(Parc::ptr_eq(&five, &same_five)); /// assert!(!Parc::ptr_eq(&five, &other_five)); /// }).unwrap(); /// ``` pub fn ptr_eq(this: &Self, other: &Self) -> bool { this.ptr.off() == other.ptr.off() } } impl<T: PSafe, A: MemPool> PmemUsage for Parc<T, A> { default fn size_of() -> usize { Ptr::<ParcInner<T, A>, A>::size_of() } } impl<T: PSafe + PmemUsage + ?Sized, A: MemPool> PmemUsage for Parc<T, A> { fn size_of() -> usize { Ptr::<ParcInner<T, A>, A>::size_of() + T::size_of() } } impl<T: PSafe + ?Sized, A: MemPool> Deref for Parc<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 Parc<T, A> { /// Drops the `Parc` 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::*; /// use crndm::sync::Parc; /// use crndm::clone::PClone; /// /// struct Foo; /// /// impl Drop for Foo { /// fn drop(&mut self) { /// println!("dropped!"); /// } /// } /// /// Heap::transaction(|j| { /// let foo = Parc::new(Foo, j); /// let foo2 = Parc::pclone(&foo, j); /// /// drop(foo); // Doesn't print anything /// drop(foo2); // Prints "dropped!" /// }).unwrap(); /// ``` /// fn drop(&mut self) { unsafe { #[cfg(not(feature = "no_log_rc"))] { let journal = Journal::<A>::current(true).unwrap(); self.log_count(journal.0); } // Because `fetch_sub` is already atomic, we do not need to synchronize // with other threads unless we are going to delete the object. This // same logic applies to the below `fetch_sub` to the `weak` count. if self.inner().counter.strong.fetch_sub(1, Release) != 1 { return; } atomic::fence(Acquire); self.drop_slow(); } } } impl<T: PSafe + ?Sized, A: MemPool> PClone<A> for Parc<T, A> { #[inline] fn pclone(&self, _journal: &Journal<A>) -> Parc<T, A> { #[cfg(not(feature = "no_log_rc"))] self.log_count(_journal); let old_size = self.inner().counter.strong.fetch_add(1, Relaxed); // However we need to guard against massive ref counts in case someone // is `mem::forget`ing Arcs. If we don't do this the count can overflow // and users will use-after free. We racily saturate to `isize::MAX` on // the assumption that there aren't ~2 billion threads incrementing // the reference count at once. This branch will never be taken in // any realistic program. // // We abort because such a program is incredibly degenerate, and we // don't care to support it. if old_size > MAX_REFCOUNT { std::process::abort(); } Self::from_inner(self.ptr) } } impl<T: RootObj<A> + PSafe, A: MemPool> RootObj<A> for Parc<T, A> { #[inline] default fn init(journal: &Journal<A>) -> Parc<T, A> { Parc::new(T::init(journal), journal) } } impl<T: Default + PSafe + ?Sized, A: MemPool> RootObj<A> for Parc<T, A> { #[inline] default fn init(journal: &Journal<A>) -> Parc<T, A> { Parc::new(T::default(), journal) } } trait RcEqIdent<T: PartialEq + PSafe + ?Sized, A: MemPool> { fn eq(&self, other: &Parc<T, A>) -> bool; fn ne(&self, other: &Parc<T, A>) -> bool; } impl<T: PartialEq + PSafe + ?Sized, A: MemPool> RcEqIdent<T, A> for Parc<T, A> { #[inline] fn eq(&self, other: &Parc<T, A>) -> bool { **self == **other } #[inline] fn ne(&self, other: &Parc<T, A>) -> bool { **self != **other } } impl<T: PartialEq + PSafe + ?Sized, A: MemPool> PartialEq for Parc<T, A> { #[inline] fn eq(&self, other: &Parc<T, A>) -> bool { RcEqIdent::eq(self, other) } } impl<T: Eq + PSafe + ?Sized, A: MemPool> Eq for Parc<T, A> {} impl<T: PartialOrd + PSafe + ?Sized, A: MemPool> PartialOrd for Parc<T, A> { #[inline(always)] fn partial_cmp(&self, other: &Parc<T, A>) -> Option<Ordering> { (**self).partial_cmp(&**other) } #[inline(always)] fn lt(&self, other: &Parc<T, A>) -> bool { **self < **other } #[inline(always)] fn le(&self, other: &Parc<T, A>) -> bool { **self <= **other } #[inline(always)] fn gt(&self, other: &Parc<T, A>) -> bool { **self > **other } #[inline(always)] fn ge(&self, other: &Parc<T, A>) -> bool { **self >= **other } } impl<T: Ord + PSafe + ?Sized, A: MemPool> Ord for Parc<T, A> { #[inline] fn cmp(&self, other: &Parc<T, A>) -> Ordering { (**self).cmp(&**other) } } impl<T: Hash + PSafe, A: MemPool> Hash for Parc<T, A> { fn hash<H: Hasher>(&self, state: &mut H) { (**self).hash(state); } } impl<T: fmt::Display + PSafe, A: MemPool> fmt::Display for Parc<T, A> { fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result { fmt::Display::fmt(&**self, f) } } impl<T: fmt::Debug + PSafe, A: MemPool> fmt::Debug for Parc<T, A> { fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result { self.deref().fmt(f) } } impl<T: PSafe + ?Sized, A: MemPool> fmt::Pointer for Parc<T, A> { fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result { fmt::Pointer::fmt(&(&**self as *const T), f) } } /// `Weak` is a version of [`Parc`] 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`]`<`[`Parc`]`<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 [`Parc`] without preventing its inner value from being /// dropped. It is also used to prevent circular references between [`Parc`] /// pointers, since mutual owning references would never allow either [`Parc`] /// to be dropped. For example, a tree could have strong [`Parc`] 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 [`Parc::downgrade`]. /// /// [`Parc::downgrade`]: ./struct.Parc.html#method.downgrade /// [`upgrade`]: #method.upgrade pub struct Weak<T: PSafe + ?Sized, A: MemPool> { ptr: Ptr<ParcInner<T, A>, A>, } impl<T: ?Sized, A: MemPool> !TxOutSafe for Weak<T, A> {} impl<T: ?Sized, A: MemPool> !Sync for Weak<T, A> {} impl<T: ?Sized, A: MemPool> !Send 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 ParcInner<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 ParcInner<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(), } } fn is_dangling(&self) -> bool { self.ptr.is_dangling() } /// Attempts to upgrade the `Weak` pointer to an [`Parc`], delaying /// dropping of the inner value if successful. /// /// Returns [`None`] if the inner value has since been dropped. /// /// # Examples /// /// ``` /// use crndm::alloc::*; /// use crndm::sync::Parc; /// /// Heap::transaction(|j| { /// let five = Parc::new(5, j); /// let weak_five = Parc::downgrade(&five, j); /// let strong_five = weak_five.upgrade(j); /// assert!(strong_five.is_some()); /// /// // Destroy all strong pointers. /// drop(strong_five); /// drop(five); /// /// assert!(weak_five.upgrade(j).is_none()); /// }).unwrap() /// ``` pub fn upgrade(&self, _journal: &Journal<A>) -> Option<Parc<T, A>> { // We use a CAS loop to increment the strong count instead of a // fetch_add because once the count hits 0 it must never be above 0. let inner = self.inner()?; // Relaxed load because any write of 0 that we can observe // leaves the field in a permanently zero state (so a // "stale" read of 0 is fine), and any other value is // confirmed via the CAS below. let mut n = inner.counter.strong.load(Relaxed); loop { if n == 0 { return None; } // See comments in `Arc::clone` for why we do this (for `mem::forget`). if n > MAX_REFCOUNT { std::process::abort(); } #[cfg(not(feature = "no_log_rc"))] inner.log_count(_journal); // Relaxed is valid for the same reason it is on Arc's Clone impl match inner .counter .strong .compare_exchange_weak(n, n + 1, Relaxed, Relaxed) { Ok(_) => return Some(Parc::from_inner(self.ptr)), // null checked above Err(old) => n = old, } } } /// Gets the number of strong (`Parc`) pointers pointing to this allocation. /// /// If `self` was created using [`Weak::new`], this will return 0. pub fn strong_count(&self) -> usize { if let Some(inner) = self.inner() { inner.counter.strong.load(SeqCst) } else { 0 } } /// Gets an approximation of the number of `Weak` pointers pointing to this /// allocation. /// /// If `self` was created using [`Weak::new`], or if there are no remaining /// strong pointers, this will return 0. /// /// # Accuracy /// /// Due to implementation details, the returned value can be off by 1 in /// either direction when other threads are manipulating any `Parc`s or /// `Weak`s pointing to the same allocation. pub fn weak_count(&self) -> usize { self.inner() .map(|inner| { let weak = inner.counter.weak.load(SeqCst); let strong = inner.counter.strong.load(SeqCst); if strong == 0 { 0 } else { // Since we observed that there was at least one strong pointer // after reading the weak count, we know that the implicit weak // reference (present whenever any strong references are alive) // was still around when we observed the weak count, and can // therefore safely subtract it. weak - 1 } }) .unwrap_or(0) } #[inline] fn inner(&self) -> Option<&ParcInner<T, A>> { if self.ptr.is_dangling() { None } else { Some(self.ptr.get_mut()) } } /// Returns `true` if the two `Weak`s point to the same allocation (similar to /// [`std::ptr::eq`]), or if both don't point to any allocation /// (because they were created with `Weak::new()`). /// /// # Notes /// /// Since this compares pointers it means that `Weak::new()` will equal each /// other, even though they don't point to any allocation. /// #[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() { #[cfg(not(feature = "no_log_rc"))] { let journal = Journal::<A>::current(true).unwrap(); _inner.log_count(journal.0); } // If we find out that we were the last weak pointer, then its time to // deallocate the data entirely. See the discussion in Arc::drop() about // the memory orderings // // It's not necessary to check for the locked state here, because the // weak count can only be locked if there was precisely one weak ref, // meaning that drop could only subsequently run ON that remaining weak // ref, which can only happen after the lock is released. let inner = if let Some(inner) = self.inner() { inner } else { return; }; if inner.counter.weak.fetch_sub(1, Release) == 1 { atomic::fence(Acquire); unsafe { A::free(self.ptr.as_mut()); } } } } } impl<T: PSafe + ?Sized, A: MemPool> PClone<A> for Weak<T, A> { #[inline] fn pclone(&self, _journal: &Journal<A>) -> Weak<T, A> { let inner = if let Some(inner) = self.inner() { inner } else { return Weak { ptr: self.ptr }; }; #[cfg(not(feature = "no_log_rc"))] inner.log_count(_journal); // See comments in Arc::clone() for why this is relaxed. This can use a // fetch_add (ignoring the lock) because the weak count is only locked // where are *no other* weak pointers in existence. (So we can't be // running this code in that case). let old_size = inner.counter.weak.fetch_add(1, Relaxed); // See comments in Arc::clone() for why we do this (for mem::forget). if old_size > MAX_REFCOUNT { std::process::abort(); } Weak { ptr: self.ptr } } } impl<T: PSafe + ?Sized + fmt::Debug, 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> Default for Weak<T, A> { fn default() -> Self { Weak::new() } } trait ParcBoxPtr<T: PSafe + ?Sized, A: MemPool> { fn count(&self) -> &Counter; #[inline] #[cfg(not(feature = "no_log_rc"))] fn log_count(&self, journal: &Journal<A>) { let inner = self.count(); unsafe { if A::contains(inner as *const _ as *const u8 as u64) { let flag = &inner.has_log as *const u8 as *mut u8; if std::intrinsics::atomic_cxchg_acqrel(flag, 0, 1).0 == 0 { inner.take_log(journal, Notifier::Atomic(Ptr::from_ref(&inner.has_log))); } } } } } impl<T: PSafe + ?Sized, A: MemPool> ParcBoxPtr<T, A> for Parc<T, A> { #[inline(always)] fn count(&self) -> &Counter { &self.ptr.counter } } impl<T: PSafe + ?Sized, A: MemPool> ParcBoxPtr<T, A> for ParcInner<T, A> { #[inline(always)] fn count(&self) -> &Counter { &self.counter } } impl<T: PSafe + ?Sized, A: MemPool> borrow::Borrow<T> for Parc<T, A> { fn borrow(&self) -> &T { &self.inner().value } } impl<T: PSafe + ?Sized, A: MemPool> AsRef<T> for Parc<T, A> { fn as_ref(&self) -> &T { &self.inner().value } } impl<T: PSafe + ?Sized, A: MemPool> Unpin for Parc<T, A> {} unsafe fn data_offset<T, 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::<ParcInner<(), A>>(); (layout.size() + layout.padding_needed_for(align)) as isize } /// `VWeak` is a version of [`Parc`] that holds a non-owning thread-safe /// reference to the managed allocation in the volatile heap. The allocation is /// accessed by calling [`upgrade`] on the `VWeak` pointer, which returns an /// [`Option`]`<`[`Parc`]`<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 thread-safe reference to /// the persistent allocation managed by [`Parc`] without preventing its inner /// value from being dropped. /// /// The typical way to obtain a `VWeak` pointer is to call [`Parc::volatile`]. /// /// [`Parc::volatile`]: ./struct.Parc.html#method.volatile /// [`upgrade`]: #method.upgrade pub struct VWeak<T: ?Sized, A: MemPool> { ptr: *const ParcInner<T, A>, valid: *mut VWeakValid, gen: u32, } 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> Send for VWeak<T, A> {} unsafe impl<T: ?Sized, A: MemPool> Sync 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(parc: &Parc<T, A>) -> VWeak<T, A> { let list = parc.ptr.vlist.as_mut(); VWeak { ptr: parc.ptr.as_ptr(), valid: list.append(), gen: A::gen(), } } /// Attempts to upgrade the `VWeak` pointer to an [`Parc`], delaying /// dropping of the inner value if successful. /// /// Returns [`None`] if the inner value has since been dropped. /// /// # Examples /// /// ``` /// use crndm::default::*; /// use std::mem::drop; /// /// type P = BuddyAlloc; /// let obj = P::open::<Root>("foo.pool", O_CF).unwrap(); /// /// struct Root(PRefCell<Option<Parc<i32>>>); /// impl RootObj<P> for Root { /// fn init(j: &Journal) -> Self { /// Root(PRefCell::new(Some(Parc::new(10, j)),j)) /// } /// } /// /// let vweak_obj = obj.0.borrow().as_ref().unwrap().volatile(); /// /// P::transaction(|j| { /// let strong_obj = vweak_obj.upgrade(j); /// assert!(strong_obj.is_some()); /// /// // Destroy all strong pointers. /// drop(strong_obj); /// *obj.0.borrow_mut(j) = None; // RootCell does not drop, so make it None /// /// assert!(vweak_obj.upgrade(j).is_none()); /// }).unwrap(); /// ``` pub fn upgrade(&self, _journal: &Journal<A>) -> Option<Parc<T, A>> { // We use a CAS loop to increment the strong count instead of a // fetch_add as this function should never take the reference count // from zero to one. let inner = self.inner()?; // Relaxed load because any write of 0 that we can observe // leaves the field in a permanently zero state (so a // "stale" read of 0 is fine), and any other value is // confirmed via the CAS below. let mut n = inner.counter.strong.load(Relaxed); loop { if n == 0 { return None; } // See comments in `Arc::clone` for why we do this (for `mem::forget`). if n > MAX_REFCOUNT { std::process::abort(); } #[cfg(not(feature = "no_log_rc"))] inner.log_count(_journal); // Relaxed is fine for the failure case because we don't have any expectations about the new state. // Acquire is necessary for the success case to synchronise with `Arc::new_cyclic`, when the inner // value can be initialized after `Weak` references have already been created. In that case, we // expect to observe the fully initialized value. match inner.counter.strong.compare_exchange_weak(n, n + 1, Acquire, Relaxed) { Ok(_) => return Some(Parc::from_inner(Ptr::from_raw(self.ptr))), // null checked above Err(old) => n = old, } } } #[inline] fn inner(&self) -> Option<&ParcInner<T, A>> { unsafe { if !(*self.valid).valid.load(Acquire) || self.gen != A::gen() { 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.load(Acquire) { 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 !this.list.is_null() { let mut head = match (*this.list).head.lock() { Ok(g) => g, Err(p) => p.into_inner(), }; 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: AtomicBool, next: *mut VWeakValid, prev: *mut VWeakValid, list: *mut VWeakList, } use std::sync::Mutex as StdMutex; struct VWeakList { head: StdMutex<*mut VWeakValid>, } impl VWeakList { fn append(&mut self) -> *mut VWeakValid { let list = self as *mut Self; let mut head = match self.head.lock() { Ok(g) => g, Err(p) => p.into_inner(), }; let new = Box::into_raw(Box::new(VWeakValid { valid: AtomicBool::new(true), next: *head, prev: std::ptr::null_mut(), list, })); if !(*head).is_null() { unsafe { (**head).prev = new; } } *head = new; new } } impl Default for VWeakList { fn default() -> Self { VWeakList { head: StdMutex::new(std::ptr::null_mut()), } } } impl Drop for VWeakList { fn drop(&mut self) { let head = match self.head.lock() { Ok(g) => g, Err(p) => p.into_inner(), }; unsafe { let mut curr = *head; while !curr.is_null() { (*curr).valid.store(false, Release); (*curr).list = std::ptr::null_mut(); curr = (*curr).next; } } } }