Struct crndm::sync::VWeak

pub struct VWeak<T: ?Sized, A: MemPool> { /* fields omitted */ }

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 upgraded. 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.

Implementations

impl<T: PSafe + ?Sized, A: MemPool> VWeak<T, A>

pub fn upgrade(&self, _journal: &Journal<A>) -> Option<Parc<T, A>>

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();

Trait Implementations

impl<T: PSafe + ?Sized, A: MemPool> Clone for VWeak<T, A>

pub fn clone(&self) -> Self

Returns a copy of the value.

pub fn clone_from(&mut self, source: &Self)

Performs copy-assignment from source.

impl<T: ?Sized, A: MemPool> Drop for VWeak<T, A>

pub fn drop(&mut self)

Executes the destructor for this type.

impl<T: ?Sized, A: MemPool> PSafe for VWeak<T, A>

impl<T: ?Sized, A: MemPool> RefUnwindSafe for VWeak<T, A>

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> TxInSafe for VWeak<T, A>

impl<T: ?Sized, A: MemPool> TxOutSafe for VWeak<T, A>

impl<T: ?Sized, A: MemPool> UnwindSafe for VWeak<T, A>