nosy

nosy is a Rust library for broadcasting messages/events such as change notifications.

The niche which nosy seeks to fill is: delivering precise change notifications (e.g. “these particular elements of this collection have changed”) from a data source to a set of listeners (observers) in such a way that

• there is no unbounded buffering of messages (as an unbounded channel would have),
• there is no blocking/suspending (as a bounded channel would have),
• there is no execution of further application logic while the message is being delivered (as plain event-listener registration would have), and
• the scheduling of the execution of said application logic is fully under application control (rather than implicitly executing some sort of work queue, as a “reactive” framework might).

The tradeoff we make in order to achieve this is that message delivery does involve execution of a small amount of code on behalf of each listener; this code is responsible for deciding whether the message is of interest, and if so, storing it or its implications for later reading. (We could say that the listeners are nosy.)

Because of this strategy, nosy is not a good choice if you expect to have very many listeners of the same character (e.g. many identical worker tasks updating their state); in those cases, you would probably be better off using a conventional broadcast channel or watch channel. It is also not a good choice if it is critical that no third-party code executes on your thread or while your function is running.

Platform requirements

nosy is compatible with no_std platforms. The minimum requirements for using nosy are the following. (All platforms which support std meet these requirements, and many others do too.)

• The alloc standard library crate, and a global allocator.
• Pointer-sized and u8-sized atomics (cfg(target_has_atomic = "ptr") and cfg(target_has_atomic = "8")).

License

Licensed under either of

• Apache License, Version 2.0 (LICENSE-APACHE or http://www.apache.org/licenses/LICENSE-2.0)
• MIT license (LICENSE-MIT or http://opensource.org/licenses/MIT)

at your option.

Contribution

Unless you explicitly state otherwise, any contribution intentionally submitted for inclusion in the work by you, as defined in the Apache-2.0 license, shall be dual licensed as above, without any additional terms or conditions.