Doesn't seem to work with wasm32-unknown-unknown

[d3lm]

I tried to use scc for a crate that we compile to wasm32-unknown-unknown. I tried to use a HashIndex as a static item and while it compiles just fine, it crashes at runtime if I try to insert an item.

Here's what I did:

static HASH_INDEX: Lazy<HashIndex<u32, u32>> = Lazy::new(|| HashIndex::default());

#[wasm_bindgen)]
pub fn some_fn() -> Result<...> {
  HASH_INDEX.insert(1, 2)?;
}

It then crashes at runtime with the following error:

panicked at .../.cargo/registry/src/index.crates.io-6f17d22bba15001f/scc-2.0.4/src/hash_table/bucket_array.rs:55:13:
assertion `left == right` failed
  left: 16
 right: 0

Here's where it throws:

Any idea what could be causing this?

[Amanieu]

Possibly related: calculate_memory_layout uses an alignment of 1 instead of the actual alignment:

scalable-concurrent-containers/src/hash_table/bucket_array.rs

Line 218 in b910716

Layout::from_size_align_unchecked(allocation_size, 1)

[d3lm]

Oh yea, that is very good point indeed. The alignment is prolly wrong.

[wvwwvwwv]

Hi, thanks for reporting this issue!

The alignment is definitely different from the actual alignment, but that is intended; if the alignment is above a certain threshold (~4?), alloc_zeroed becomes awfully slow due to a call to memset, otherwise alloc_zeroed is simply translated into calloc which takes full advantage of demand paging.

I think the problem is related to wasm32 because this crate has never been tested on a 32-bit machine.

I'll try to fix it on this weekend!

[wvwwvwwv]

Reproduced the issue and fixed it.

Cause: the size of the Bucket struct is no longer a power of two in a 32-bit binary.

I'll cleanup the change, add more tests, and then upload SCC 2.0.5 soon.

[wvwwvwwv]

The commit message is wrong, but the issue was fixed in 33e4fc5

[wvwwvwwv]

Fixed in 2.0.5!

-> Theoretically, everything shall work as expected in a 32-bit binary.
-> If you find anything unexpected, please open a new issue, or reopen this one in case it's related to this.

[d3lm]

Oh wow, thanks so much for that insanely fast turnaround! I really appreciate it 🙏