[−][src]Crate refpool
A reimplementation of std::rc::Rc
which uses a pool of reusable
memory to speed up reallocation.
Prerequisites
In order to initialise a type to its default value from the memory pool
using PoolRef::default()
, it needs to implement
PoolDefault
.
If you want to be able to use PoolRef::make_mut()
, it
also needs to implement PoolClone
.
For constructing values using PoolRef::new()
, there's no
requirement.
There are implementations for PoolDefault
and
PoolClone
for most primitive types and a good selection of
std
's data types, and you can easily provide default implementations for
your own types by implementing the marker trait
PoolDefaultImpl
. You can also implement your own if you
have data structures whose memory doesn't need to be fully intitialised at
construction time, which can give you a slight performance boost. (This
optimisation is why PoolDefault
and
PoolClone
exist as distinct traits, otherwise
Default
and Clone
would have sufficed.)
Usage
You create new values by calling
PoolRef::default(pool)
or PoolRef::new(pool, value)
. This will use memory from the pool if available,
falling back to a normal heap allocation if the pool is empty. When the
last PoolRef
referencing the value is dropped, its allocated
memory is returned to the pool.
Differences from Rc
PoolRef
is API compatible with Rc
, with the following
exceptions:
- Types handled by the pool must be
Sized
. This means the pool won't accept trait objects, ie. noPool<dyn A>
. - Constructors need a
Pool
argument, so they're necessarily different: instead ofRc::new(value)
, you havePoolRef::default(pool)
to construct a default value andPoolRef::new(pool, value)
as the equivalent ofRc::new(value)
. - It does not implement
Default
, because you need aPool
argument to construct an instance. UsePoolRef::default(pool)
. - There's currently no equivalent to
Weak
. - Experimental APIs are not implemented.
Example
// Create a pool of `usize` with a max size of 1 (for argument's sake). let mut pool: Pool<usize> = Pool::new(1); { // Create a reference handle to a usize initialised to 0. // The pool starts out empty, so this triggers a normal heap alloc. let value_ref = PoolRef::default(&mut pool); assert_eq!(0, *value_ref); // You can deref it just like `Rc`. } // `value_ref` is dropped here, and its heap memory goes on the pool. // Check that we do indeed have one allocation in the pool now. assert_eq!(1, pool.get_pool_size()); // Create another reference and initialise it to 31337, a good round number. // This will reuse `value_ref`'s memory. let another_value_ref = PoolRef::new(&mut pool, 31337); assert_eq!(31337, *another_value_ref); // Check that the pool is again empty after we reused the previous memory. assert_eq!(0, pool.get_pool_size());
Structs
Pool | A pool of preallocated memory sized to match type |
PoolRef | A reference counted pointer to |
Traits
PoolClone | A trait for cloning a value into a |
PoolDefault | A trait for initialising a |
PoolDefaultImpl | A marker trait for types which should be fully initialised. |