Tokio GenServer

A simple Elixir/Erlang-GenServer-like actor implementation on Tokio.

Please see the documentation for information on usage and examples.

• Simple: Define 3 messages types and at least one callback, and you have an actor. No macro magic. No global "system"s or "pollution".
• Powerful: Initialization and exit callbacks. On completion, returns the actor itself, the whole running environment, and run result.
• Lightweight: Little code. No boxing except the ones introduced by Tokio.
• Blocking aCTOR (Bctor) for use with synchronous code.

NB: What is a GenServer? A Generic Server is a persistent process that handles messages sent to it. That's it. The message can either be a cast (fire-and-forget) or a call (request-response).

Major difference from Erlang

• Do not panic (crash). Return anyhow::Error instead.
• Tokio scheduling is cooperative, not preemptive. Your long-running async code should call yield_now in the middle so they can be interrupted.
• Blanket supervision implementations are not very useful. Instead, let your actors spawn children actors, and let children send messages to their parents using before_exit to handle children exiting.

Alternatives

Hydra:

• 👍 Implements "proper" "process"; interfaces closer to Erlang.
• 👍 Type-erasure on "child", "pid".
• 👍 Supervisors.
• 👍 Multi-node.
• ❓ Catches unwind (also bad because of overhead?).
• ❓ Uses flume channels: may be faster, but more dependencies.
• 👎 Requires creating "applications" and "pollutes" the codebase.
• 👎 Call, cast, and reply message types are not distinguished.
• 👎 Uses magic global variables to manage "processes".
• 👎 No blocking.
• 👎 Requires messages to be serializable.
• 👎 Most traits are not object-safe.