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use std::{mem, fmt};
use std::ops::{Deref, DerefMut};
use std::cell::RefCell;
use std::rc::Rc;
use super::Chunk;
pub struct SlicePoolRef<'a, T: 'a>(Rc<RefCell<ChunkableInner<'a, T>>>);
impl<'a, T> SlicePoolRef<'a, T> {
pub fn new(slice: &'a mut [T]) -> Self {
SlicePoolRef(Rc::new(RefCell::new(ChunkableInner {
values: vec![Chunk { size: slice.len(), offset: 0, free: true }],
memory: slice,
})))
}
pub fn allocate(&mut self, size: usize) -> Option<PoolRef<'a, T>> {
(*self.0).borrow_mut()
.allocate(size)
.map(|slice| PoolRef { inner: self.0.clone(), data: slice })
}
pub fn as_ptr(&self) -> *const T {
(*self.0).borrow().memory.deref().as_ref().as_ptr()
}
pub fn len(&self) -> usize {
(*self.0).borrow().memory.len()
}
}
pub struct PoolRef<'a, T: 'a> {
inner: Rc<RefCell<ChunkableInner<'a, T>>>,
data: &'a mut [T],
}
impl<'a, T: fmt::Debug> fmt::Debug for PoolRef<'a, T> {
fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
write!(f, "{:?}", self.deref())
}
}
impl<'a, T> Deref for PoolRef<'a, T> {
type Target = [T];
fn deref<'b>(&'b self) -> &'b Self::Target {
&self.data
}
}
impl<'a, T> DerefMut for PoolRef<'a, T> {
fn deref_mut<'b>(&'b mut self) -> &'b mut [T] {
self.data
}
}
impl<'a, T> Drop for PoolRef<'a, T> {
fn drop(&mut self) {
unsafe { (*self.inner).borrow_mut().release(self.data) };
}
}
struct ChunkableInner<'a, T: 'a> {
values: Vec<Chunk>,
memory: &'a mut [T],
}
impl<'a, T> ChunkableInner<'a, T> {
fn allocate(&mut self, size: usize) -> Option<&'a mut [T]> {
if let Some(index) = self.values.iter().position(|chunk| chunk.free && chunk.size >= size) {
let mut chunk = self.values[index].clone();
let chunk_range = chunk.offset..(chunk.offset + size);
let delta_size = chunk.size - size;
chunk.size -= delta_size;
chunk.free = false;
self.values[index] = chunk;
if delta_size > 0 {
let adjacent_index = index + 1;
self.values.insert(adjacent_index, Chunk {
offset: chunk_range.end,
size: delta_size,
free: true
});
self.defragment(adjacent_index);
}
Some(unsafe {
mem::transmute(&mut self.memory[chunk_range])
})
} else {
None
}
}
unsafe fn release(&mut self, slice: &mut [T]) {
let index = self.values.iter().position(|chunk| {
self.memory.as_ptr().offset(chunk.offset as isize) == slice.as_ptr()
}).unwrap();
self.values[index].free = true;
self.defragment(index);
}
fn defragment(&mut self, index: usize) {
let adjacent_index = index + 1;
if self.values.get(adjacent_index).iter().any(|chunk| chunk.free) {
self.values[index].size += self.values[adjacent_index].size;
self.values.remove(adjacent_index);
}
if index > 0 && self.values[index - 1].free {
self.values[index - 1].size += self.values[index].size;
self.values.remove(index);
}
}
}