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|
use std::alloc::{
self,
Layout,
};
use std::cell::Cell;
use std::ptr::{
self,
NonNull,
};
use std::slice;
use std::sync::Mutex;
use crate::err;
#[derive(Copy, Clone)]
struct RawBlock {
ptr: NonNull<u8>,
layout: Layout,
}
pub struct GlobalArena {
blksz: usize,
blocks: Mutex<Vec<RawBlock>>,
}
impl GlobalArena {
pub fn new(blksz: usize) -> Self {
Self {
blksz,
blocks: Mutex::new(Vec::new()),
}
}
fn allocate_block(&self, layout: Layout) -> RawBlock {
let layout = Layout::from_size_align(
layout.size().max(self.blksz),
layout.align(),
)
.unwrap_or_else(|e| err!(e, "allocation error"));
let ptr = NonNull::new(unsafe { alloc::alloc(layout) })
.unwrap_or_else(|| alloc::handle_alloc_error(layout));
let block = RawBlock { ptr, layout };
self.blocks.lock().unwrap().push(block.clone());
return block;
}
}
impl Drop for GlobalArena {
fn drop(&mut self) {
for block in self.blocks.lock().unwrap().iter() {
unsafe {
alloc::dealloc(block.ptr.as_ptr(), block.layout);
}
}
}
}
pub struct LocalArena<'a> {
parent: &'a GlobalArena,
cursor: Cell<*mut u8>,
end: Cell<*mut u8>,
}
impl<'a> LocalArena<'a> {
pub fn new(parent: &'a GlobalArena) -> Self {
return Self {
parent,
cursor: Cell::new(ptr::null_mut()),
end: Cell::new(ptr::null_mut()),
};
}
fn alloc_raw(&self, layout: Layout) -> NonNull<u8> {
let cursor = self.cursor.get() as usize;
let align_offset =
cursor.wrapping_add(layout.align() - 1) & !(layout.align() - 1);
let Some(next_cursor) = align_offset.checked_add(layout.size()) else {
err!("allocation overflow");
};
return if next_cursor <= self.end.get() as usize {
self.cursor.set(next_cursor as *mut u8);
unsafe { NonNull::new_unchecked(align_offset as *mut u8) }
} else {
self.alloc_slow(layout)
};
}
#[cold]
fn alloc_slow(&self, layout: Layout) -> NonNull<u8> {
let block = self.parent.allocate_block(layout);
let beg = block.ptr.as_ptr() as usize;
let end = beg + block.layout.size();
let next_cursor = beg + layout.size();
self.cursor.set(next_cursor as *mut u8);
self.end.set(end as *mut u8);
return unsafe { NonNull::new_unchecked(beg as *mut u8) };
}
pub fn alloc<T>(&self, value: T) -> &'a mut T {
let ptr = self.alloc_raw(Layout::new::<T>()).cast::<T>().as_ptr();
unsafe {
ptr::write(ptr, value);
return &mut *ptr;
}
}
pub fn alloc_slice<T>(&self, len: usize) -> &'a mut [T] {
let layout = Layout::array::<T>(len)
.unwrap_or_else(|e| err!(e, "allocation error"));
let ptr = self.alloc_raw(layout).cast::<T>().as_ptr();
return unsafe { slice::from_raw_parts_mut(ptr, len) };
}
}
#[test]
fn test_alloc_slice() {
let arena_global = GlobalArena::new(8);
let arena_local_1 = LocalArena::new(&arena_global);
let arena_local_2 = LocalArena::new(&arena_global);
let s1 = arena_local_1.alloc_slice(8);
let s2 = arena_local_2.alloc_slice(4);
assert_eq!(s1.len(), 8);
assert_eq!(s2.len(), 4);
for i in 0..s1.len() {
s1[i] = i;
}
for i in 0..s2.len() {
s2[i] = i;
}
}
#[test]
fn test_arena_grows() {
let arena_global = GlobalArena::new(8);
let arena_local = LocalArena::new(&arena_global);
let s1 = arena_local.alloc_slice(8);
let s2 = arena_local.alloc_slice(69);
assert_eq!(s1.len(), 8);
assert_eq!(s2.len(), 69);
for i in 0..s1.len() {
s1[i] = i;
}
for i in 0..s2.len() {
s2[i] = i;
}
}
|
