70 lines
2.2 KiB
Rust
70 lines
2.2 KiB
Rust
//! Addressing a gen_server by a durable name.
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//!
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//! A gen_server is multi-message (call / cast over one inbox), so it is named
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//! by the *server* type rather than by a single message type. Registering it
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//! under a [`GenServerName`] lets clients `call` and `cast` by name, resolving on
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//! every use — so the address keeps working across a supervised restart, with
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//! no stale [`GenServerRef`] to refresh.
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use smarm::{call, cast, run, whereis_server, GenServer, GenServerBuilder, GenServerName, GenServerRef};
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/// A counter server: synchronous `Get`, asynchronous `Inc` / `Add`.
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struct Counter {
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n: u64,
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}
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enum Query {
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Get,
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}
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enum Update {
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Inc,
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Add(u64),
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}
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impl GenServer for Counter {
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type Call = Query;
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type Reply = u64;
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type Cast = Update;
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type Info = ();
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type Timer = ();
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fn handle_call(&mut self, q: Query) -> u64 {
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match q {
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Query::Get => self.n,
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}
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}
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fn handle_cast(&mut self, u: Update) {
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match u {
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Update::Inc => self.n += 1,
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Update::Add(k) => self.n += k,
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}
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}
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}
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/// A durable name typed by the server, so by-name `call` / `cast` check against
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/// `Counter`'s `Call` / `Cast` / `Reply`.
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const COUNTER: GenServerName<Counter> = GenServerName::new("counter");
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fn main() {
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run(|| {
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// Start the server and bind its name in one step. A named start is
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// fallible: the name may already be held by another live server.
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GenServerBuilder::new(Counter { n: 0 })
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.named(COUNTER)
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.start()
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.unwrap();
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// Address it purely by name. Each call/cast resolves through the
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// registry, so a server restarted under the same name is reached
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// transparently.
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cast(COUNTER, Update::Inc).unwrap();
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cast(COUNTER, Update::Add(41)).unwrap();
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assert_eq!(call(COUNTER, Query::Get).unwrap(), 42);
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// When you want a handle to hold or pass on rather than resolve per
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// call, recover a typed `GenServerRef` from the name.
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let svc: Option<GenServerRef<Counter>> = whereis_server(COUNTER);
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if let Some(svc) = svc {
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let _ = svc.call(Query::Get);
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}
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});
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}
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