[Panic] Attempt to add with overflow during insert

[JoshLind]

Hi, we recently started using mini-moka to cache and retrieve data, but we've run into an unusual panic during an insert call. The panic seems rare, but this is the cleaned up stacktrace:

details = \"panicked at 'attempt to add with overflow', /usr/local/cargo/registry/src/index.crates.io-6f17d22bba15001f/mini-moka-0.10.2/src/common/frequency_sketch.rs:183:9\"
backtrace = \"\"\"\n
...
9:     0x56217dd61123 - mini_moka::common::frequency_sketch::FrequencySketch::increment::h702da432b2c28c0d 
10:     0x56217d5d5a31 - mini_moka::sync::base_cache::Inner<K,V,S>::apply_reads::h89098547f143cebc
at /usr/local/cargo/registry/src/index.crates.io-6f17d22bba15001f/mini-moka-0.10.2/src/sync/base_cache.rs:782:35. <mini_moka::sync::base_cache::Inner<K,V,S> as mini_moka::common::concurrent::housekeeper::InnerSync>::sync::h8c6497ded41ff4dd
at /usr/local/cargo/registry/src/index.crates.io-6f17d22bba15001f/mini-moka-0.10.2/src/sync/base_cache.rs:664:17\n 
11:     0x56217d41c561 - mini_moka::common::concurrent::housekeeper::Housekeeper::try_sync::h45ebd0c867b7d29e\n                               
at /usr/local/cargo/registry/src/index.crates.io-6f17d22bba15001f/mini-moka-0.10.2/src/common/concurrent/housekeeper.rs:61:17\n                           mini_moka::sync::base_cache::BaseCache<K,V,S>::apply_reads_writes_if_needed::hf2dc1456ae08dd31\n                               
at /usr/local/cargo/registry/src/index.crates.io-6f17d22bba15001f/mini-moka-0.10.2/src/sync/base_cache.rs:211:17\n                           mini_moka::sync::cache::Cache<K,V,S>::schedule_write_op::he092ec6fa514b5e5\n                               
at /usr/local/cargo/registry/src/index.crates.io-6f17d22bba15001f/mini-moka-0.10.2/src/sync/cache.rs:588:13\n                           mini_moka::sync::cache::Cache<K,V,S>::insert_with_hash::h07b1808c0524e791\n                               
at /usr/local/cargo/registry/src/index.crates.io-6f17d22bba15001f/mini-moka-0.10.2/src/sync/cache.rs:447:9\n                           mini_moka::sync::cache::Cache<K,V,S>::insert::hff040ece82fbc7a4\n                               
at /usr/local/cargo/registry/src/index.crates.io-6f17d22bba15001f/mini-moka-0.10.2/src/sync/cache.rs:441:9

It seems like the panic is occurring here: https://github.com/moka-rs/mini-moka/blob/main/src/common/frequency_sketch.rs#L183.

We're not really doing anything unusual. We're importing mini-moka:

mini-moka = { version = "0.10.2", features = ["sync"] }

Creating a new Cache in our code (with no overrides):

let cache = Cache::new(500);

And (on separate tokio threads) simply calling get and insert depending on reads/writes to the cache. Perhaps this is some type of race condition? Or maybe the addition needs to use wrapping_add, too?

Our rust version is: 1.72.1

Thanks for your help :)

[tatsuya6502]

Thank you for reporting!

Or maybe the addition needs to use wrapping_add, too?

Ah, you are right. Sorry, the same bug was found and fixed in moka in last May, but I forgot to apply the fix to mini-moka.

• Fix occasional panic in FrequencySketch in debug build moka#272

I will fix mini-moka and publish a new point-release soon.

[tatsuya6502]

Thanks again for reporting this bug. I fixed it via #23 and published v0.10.3 to crates.io.

[JoshLind]

Awesome, thanks so much @tatsuya6502 😄