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perf: cache BaseVec len in Cell<u64> to avoid stable memory reads #415

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perf: cache BaseVec len in Cell<u64> to avoid stable memory reads #415

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7 changes: 6 additions & 1 deletion src/base_vec.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -37,6 +37,7 @@ use crate::{
Memory, Storable,
};
use std::borrow::{Borrow, Cow};
use std::cell::Cell;
use std::cmp::min;
use std::fmt;
use std::marker::PhantomData;
Expand Down Expand Up @@ -95,6 +96,7 @@ impl std::error::Error for InitError {}

pub struct BaseVec<T: Storable, M: Memory> {
memory: M,
cached_len: Cell<u64>,
_marker: PhantomData<T>,
}

Expand All @@ -117,6 +119,7 @@ impl<T: Storable, M: Memory> BaseVec<T, M> {
Self::write_header(&header, &memory)?;
Ok(Self {
memory,
cached_len: Cell::new(0),
_marker: PhantomData,
})
}
Expand Down Expand Up @@ -148,6 +151,7 @@ impl<T: Storable, M: Memory> BaseVec<T, M> {

Ok(Self {
memory,
cached_len: Cell::new(header.len),
_marker: PhantomData,
})
}
Expand All @@ -168,7 +172,7 @@ impl<T: Storable, M: Memory> BaseVec<T, M> {
///
/// Complexity: O(1)
pub fn len(&self) -> u64 {
read_u64(&self.memory, Address::from(LEN_OFFSET))
self.cached_len.get()
}

/// Sets the item at the specified index to the specified value.
Expand Down Expand Up @@ -254,6 +258,7 @@ impl<T: Storable, M: Memory> BaseVec<T, M> {
/// Sets the vector's length.
fn set_len(&self, new_len: u64) {
write_u64(&self.memory, Address::from(LEN_OFFSET), new_len);
self.cached_len.set(new_len);
}

/// Writes the size of the item at the specified offset.
Expand Down
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