etseidl commented on code in PR #8898:
URL: https://github.com/apache/arrow-rs/pull/8898#discussion_r2547814034
##########
parquet/src/file/metadata/memory.rs:
##########
@@ -95,21 +95,16 @@ impl<K: HeapSize, V: HeapSize> HeapSize for HashMap<K, V> {
impl<T: HeapSize> HeapSize for Arc<T> {
fn heap_size(&self) -> usize {
- // Arc stores weak and strong counts on the heap alongside an instance
of T
- 2 * std::mem::size_of::<usize>() + std::mem::size_of::<T>() +
self.as_ref().heap_size()
- }
-}
-
-impl HeapSize for Arc<dyn HeapSize> {
- fn heap_size(&self) -> usize {
- 2 * std::mem::size_of::<usize>()
- + std::mem::size_of_val(self.as_ref())
- + self.as_ref().heap_size()
+ // Do not count the size of the Arc itself that is accounted for by the
+ // caller (the object that contains the Arc).
+ std::mem::size_of::<T>() + self.as_ref().heap_size()
Review Comment:
from `Box::new`
```rust
let x: Box<_> = Box::new(ArcInner {
strong: atomic::AtomicUsize::new(1),
weak: atomic::AtomicUsize::new(1),
data,
});
```
`strong` and `weak` are also on the heap, along with the `T` data.
`size_of::<Arc<_>>` returns 8, which is what I believe is accounted for in
the size of the containers.
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