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

benchmarks/io_chunks/canbench_results.yml

@@ -44,42 +44,42 @@ benches:
   read_chunks_vec_1:
     total:
       calls: 1
-      instructions: 104859760
+      instructions: 104859642
       heap_increase: 0
       stable_memory_increase: 0
     scopes: {}
   read_chunks_vec_1k:
     total:
       calls: 1
-      instructions: 105826498
+      instructions: 105511618
       heap_increase: 0
       stable_memory_increase: 0
     scopes: {}
   read_chunks_vec_1m:
     total:
       calls: 1
-      instructions: 1010905944
+      instructions: 696002618
       heap_increase: 0
       stable_memory_increase: 0
     scopes: {}
   write_chunks_btreemap_1:
     total:
       calls: 1
-      instructions: 357205397
+      instructions: 360207245
       heap_increase: 13
       stable_memory_increase: 1536
     scopes: {}
   write_chunks_btreemap_1k:
     total:
       calls: 1
-      instructions: 4187119879
+      instructions: 4194582593
       heap_increase: 2
       stable_memory_increase: 1536
     scopes: {}
   write_chunks_btreemap_1m:
     total:
       calls: 1
-      instructions: 83659829857
+      instructions: 83673829307
       heap_increase: 0
       stable_memory_increase: 3072
     scopes: {}
@@ -107,21 +107,21 @@ benches:
   write_chunks_vec_1:
     total:
       calls: 1
-      instructions: 549903573
+      instructions: 549903446
       heap_increase: 0
       stable_memory_increase: 1536
     scopes: {}
   write_chunks_vec_1k:
     total:
       calls: 1
-      instructions: 562257515
+      instructions: 562132513
       heap_increase: 0
       stable_memory_increase: 1536
     scopes: {}
   write_chunks_vec_1m:
     total:
       calls: 1
-      instructions: 1896593101
+      instructions: 1771593099
       heap_increase: 0
       stable_memory_increase: 1536
     scopes: {}

benchmarks/vec/canbench_results.yml

@@ -2,112 +2,112 @@ benches:
   vec_get_blob_128:
     total:
       calls: 1
-      instructions: 19246661
+      instructions: 18706659
       heap_increase: 0
       stable_memory_increase: 0
     scopes: {}
   vec_get_blob_16:
     total:
       calls: 1
-      instructions: 6405945
+      instructions: 5897185
       heap_increase: 0
       stable_memory_increase: 0
     scopes: {}
   vec_get_blob_32:
     total:
       calls: 1
-      instructions: 7123504
+      instructions: 6654118
       heap_increase: 0
       stable_memory_increase: 0
     scopes: {}
   vec_get_blob_4:
     total:
       calls: 1
-      instructions: 4824326
+      instructions: 4284326
       heap_increase: 0
       stable_memory_increase: 0
     scopes: {}
   vec_get_blob_4_mem_manager:
     total:
       calls: 1
-      instructions: 7191676
+      instructions: 5891676
       heap_increase: 0
       stable_memory_increase: 0
     scopes: {}
   vec_get_blob_64:
     total:
       calls: 1
-      instructions: 11310943
+      instructions: 10751237
       heap_increase: 0
       stable_memory_increase: 0
     scopes: {}
   vec_get_blob_64_mem_manager:
     total:
       calls: 1
-      instructions: 13651091
+      instructions: 12331385
       heap_increase: 0
       stable_memory_increase: 0
     scopes: {}
   vec_get_blob_8:
     total:
       calls: 1
-      instructions: 5723200
+      instructions: 5213200
       heap_increase: 0
       stable_memory_increase: 0
     scopes: {}
   vec_get_u64:
     total:
       calls: 1
-      instructions: 4790305
+      instructions: 3530307
       heap_increase: 0
       stable_memory_increase: 0
     scopes: {}
   vec_insert_blob_128:
     total:
       calls: 1
-      instructions: 4171424
+      instructions: 3821424
       heap_increase: 0
       stable_memory_increase: 19
     scopes: {}
   vec_insert_blob_16:
     total:
       calls: 1
-      instructions: 3336227
+      instructions: 2986227
       heap_increase: 0
       stable_memory_increase: 2
     scopes: {}
   vec_insert_blob_32:
     total:
       calls: 1
-      instructions: 3455467
+      instructions: 3105467
       heap_increase: 0
       stable_memory_increase: 5
     scopes: {}
   vec_insert_blob_4:
     total:
       calls: 1
-      instructions: 3247468
+      instructions: 2897468
       heap_increase: 0
       stable_memory_increase: 0
     scopes: {}
   vec_insert_blob_64:
     total:
       calls: 1
-      instructions: 3695804
+      instructions: 3345804
       heap_increase: 0
       stable_memory_increase: 9
     scopes: {}
   vec_insert_blob_8:
     total:
       calls: 1
-      instructions: 3276889
+      instructions: 2926889
       heap_increase: 0
       stable_memory_increase: 1
     scopes: {}
   vec_insert_u64:
     total:
       calls: 1
-      instructions: 5379519
+      instructions: 4999519
       heap_increase: 0
       stable_memory_increase: 1
     scopes: {}

src/base_vec.rs

@@ -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;
@@ -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>,
 }
 
@@ -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,
         })
     }
@@ -148,6 +151,7 @@ impl<T: Storable, M: Memory> BaseVec<T, M> {
 
         Ok(Self {
             memory,
+            cached_len: Cell::new(header.len),
             _marker: PhantomData,
         })
     }
@@ -178,7 +182,7 @@ 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.
@@ -264,6 +268,7 @@ 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.