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Spawn local #1148

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merged 4 commits into from
Jan 7, 2019
Merged

Spawn local #1148

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c849ef3
Add naive spawn_local implementation + tests
derekdreery Jan 5, 2019
25ac454
Docs
derekdreery Jan 5, 2019
73913c9
Relax bound on Future
derekdreery Jan 5, 2019
687fc27
Revert previous change.
derekdreery Jan 7, 2019
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19 changes: 19 additions & 0 deletions crates/futures/src/lib.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -377,3 +377,22 @@ fn _future_to_promise(future: Box<Future<Item = JsValue, Error = JsValue>>) -> P
}
}
}

/// Converts a Rust `Future` on a local task queue.
///
/// The `future` provided must adhere to `'static` because it'll be scheduled
/// to run in the background and cannot contain any stack references.
///
/// # Panics
///
/// This function has the same panic behavior as `future_to_promise`.
pub fn spawn_local<F>(future: F)
where
F: Future<Item=(), Error=()> + 'static,
{
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@lcnr lcnr Jan 5, 2019 •
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Is there a reason why only a F: Future<Item = (), Error = ()> is allowed?
I would personally prefer

pub fn spawn_local(future: impl Future + 'static) {
    future_to_promise(
        future
            .map(|_| JsValue::undefined())
            .map_err(|_| JsValue::undefined()),
    );
}

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I changed this to what you suggest :)

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@Pauan Pauan Jan 6, 2019 •
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@lcnr It is standard practice to require (). See tokio::run and stdweb::spawn_local.

The reason this is done is to prevent mistakes, and also to force the user to handle errors (rather than silently ignoring them, which is very bad!)

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Happy to do it either way. Maybe we should match other libraries though @lcnr. You can always make your own wrapper

pub fn spawn_local(future: impl Future + 'static) {
    wasm_bindgen_futures::spawn_local(
        future.map(|_| ()).map_err(|_| ())
    )
}

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I thought about it and agree with @Pauan .

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woop consensus.

future_to_promise(
future
.map(|()| JsValue::undefined())
.map_err(|()| JsValue::undefined()),
);
}
20 changes: 19 additions & 1 deletion crates/futures/tests/tests.rs
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Expand Up @@ -9,7 +9,7 @@ extern crate wasm_bindgen_test;
use futures::unsync::oneshot;
use futures::Future;
use wasm_bindgen::prelude::*;
use wasm_bindgen_futures::{future_to_promise, JsFuture};
use wasm_bindgen_futures::{future_to_promise, spawn_local, JsFuture};
use wasm_bindgen_test::*;

#[wasm_bindgen_test(async)]
Expand Down Expand Up @@ -68,3 +68,21 @@ fn oneshot_works() -> impl Future<Item = (), Error = JsValue> {
closure.forget();
rx.then(|_| Ok(()))
}

#[wasm_bindgen_test(async)]
fn spawn_local_runs() -> impl Future<Item = (), Error = JsValue> {
let (tx, rx) = oneshot::channel::<u32>();
let fn_box = Box::new(move || {
tx.send(42).unwrap();
});
spawn_local(futures::future::ok::<(), ()>(()).map(|_| {
fn_box();
}));
rx.then(|val| {
if val == Ok(42) {
Ok(())
} else {
Err(JsValue::undefined())
}
})
}