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introduce Table and use for interned values
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| Original file line number | Diff line number | Diff line change |
|---|---|---|
| @@ -0,0 +1,133 @@ | ||
| use std::{any::Any, mem::MaybeUninit}; | ||
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| use append_only_vec::AppendOnlyVec; | ||
| use crossbeam::atomic::AtomicCell; | ||
| use parking_lot::Mutex; | ||
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| use crate::{Id, IngredientIndex}; | ||
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| const PAGE_LEN_BITS: usize = 10; | ||
| const PAGE_LEN_MASK: usize = PAGE_LEN - 1; | ||
| const PAGE_LEN: usize = 1 << PAGE_LEN_BITS; | ||
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| pub struct Table { | ||
| pages: AppendOnlyVec<Box<dyn Any + Send + Sync>>, | ||
| } | ||
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| pub struct Page<T: Any + Send + Sync> { | ||
| /// The ingredient for elements on this page. | ||
| #[allow(dead_code)] // pretty sure we'll need this eventually | ||
| ingredient: IngredientIndex, | ||
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| /// Number of elements of `data` that are initialized. | ||
| allocated: AtomicCell<usize>, | ||
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| /// The "allocation lock" is held when we allocate a new entry. | ||
| /// | ||
| /// It ensures that we can load the index, initialize it, and then update the length atomically | ||
| /// with respect to other allocations. | ||
| /// | ||
| /// We could avoid it if we wanted, we'd just have to be a bit fancier in our reasoning | ||
| /// (for example, the bounds check in `Page::get` no longer suffices to truly guarantee | ||
| /// that the data is initialized). | ||
| allocation_lock: Mutex<()>, | ||
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| /// Vector with data. This is always created with the capacity/length of `PAGE_LEN` | ||
| /// and uninitialized data. As we initialize new entries, we increment `allocated`. | ||
| data: Vec<MaybeUninit<T>>, | ||
| } | ||
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| #[derive(Copy, Clone)] | ||
| pub struct PageIndex(usize); | ||
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| #[derive(Copy, Clone)] | ||
| pub struct SlotIndex(usize); | ||
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| impl Default for Table { | ||
| fn default() -> Self { | ||
| Self { | ||
| pages: AppendOnlyVec::new(), | ||
| } | ||
| } | ||
| } | ||
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| impl Table { | ||
| pub fn get<T: Any + Send + Sync>(&self, id: Id) -> &T { | ||
| let (page, slot) = split_id(id); | ||
| let page_ref = self.page::<T>(page); | ||
| page_ref.get(slot) | ||
| } | ||
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| pub fn page<T: Any + Send + Sync>(&self, page: PageIndex) -> &Page<T> { | ||
| self.pages[page.0].downcast_ref::<Page<T>>().unwrap() | ||
| } | ||
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| pub fn push_page<T: Any + Send + Sync>(&self, ingredient: IngredientIndex) -> PageIndex { | ||
| let page = Box::new(<Page<T>>::new(ingredient)); | ||
| PageIndex(self.pages.push(page)) | ||
| } | ||
| } | ||
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| impl<T: Any + Send + Sync> Page<T> { | ||
| fn new(ingredient: IngredientIndex) -> Self { | ||
| let mut data = Vec::with_capacity(PAGE_LEN); | ||
| unsafe { | ||
| data.set_len(PAGE_LEN); | ||
| } | ||
| Self { | ||
| ingredient, | ||
| allocated: Default::default(), | ||
| allocation_lock: Default::default(), | ||
| data, | ||
| } | ||
| } | ||
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| pub(crate) fn get(&self, slot: SlotIndex) -> &T { | ||
| let len = self.allocated.load(); | ||
| assert!(slot.0 < len); | ||
| unsafe { self.data[slot.0].assume_init_ref() } | ||
| } | ||
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| pub(crate) fn allocate(&self, page: PageIndex, value: T) -> Result<Id, T> { | ||
| let guard = self.allocation_lock.lock(); | ||
| let index = self.allocated.load(); | ||
| if index == PAGE_LEN { | ||
| return Err(value); | ||
| } | ||
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| let data = &self.data[index]; | ||
| let data = data.as_ptr() as *mut T; | ||
| unsafe { std::ptr::write(data, value) }; | ||
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| self.allocated.store(index + 1); | ||
| drop(guard); | ||
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| Ok(make_id(page, SlotIndex(index))) | ||
| } | ||
| } | ||
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| impl<T: Any + Send + Sync> Drop for Page<T> { | ||
| fn drop(&mut self) { | ||
| let mut data = std::mem::replace(&mut self.data, vec![]); | ||
| let len = self.allocated.load(); | ||
| unsafe { | ||
| data.set_len(len); | ||
| drop(std::mem::transmute::<Vec<MaybeUninit<T>>, Vec<T>>(data)); | ||
| } | ||
| } | ||
| } | ||
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| fn make_id(page: PageIndex, slot: SlotIndex) -> Id { | ||
| assert!(slot.0 < PAGE_LEN); | ||
| assert!(page.0 < (1 << (32 - PAGE_LEN_BITS))); | ||
| let page = page.0 as u32; | ||
| let slot = slot.0 as u32; | ||
| Id::from_u32(page << PAGE_LEN_BITS | slot) | ||
| } | ||
|
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| fn split_id(id: Id) -> (PageIndex, SlotIndex) { | ||
| let id = id.as_u32() as usize; | ||
| let slot = id & PAGE_LEN_MASK; | ||
| let page = id >> PAGE_LEN_BITS; | ||
| (PageIndex(page), SlotIndex(slot)) | ||
| } |
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