I'm using the smol library from Rust. None of the other answers to this question helped.
The smol's Executor::spawn() is declared like so:
pub fn spawn<T: Send + 'a>(&self, future: impl Future<Output = T> + Send + 'a) -> Task<T> {
Now I have a function and want to call spawn recursively like so:
async fn start(executor: &Executor<'_>) {
let server_task = executor.spawn(async {
executor.spawn(async { println!("hello"); }).await;
});
}
But I'm getting this error:
9 | async fn start(executor: &Executor<'_>) {
| ------------ -
| |
| this parameter and the return type are declared with different lifetimes...
...
18 | let server_task = executor.spawn(async {
| ^^^^^ ...but data from `executor` is returned here
How can I resolve this error? I'm very confused.
use {
smol::{block_on, Executor},
std::sync::Arc,
};
// --
fn main() {
let ex = Arc::new(Executor::new());
block_on(ex.run(start(ex.clone())));
}
async fn start(executor: Arc<Executor<'_>>) {
let ex2 = executor.clone();
let server_task = executor.spawn(async move {
let t = ex2.spawn(async {
println!("hello");
});
t.await;
});
server_task.await;
}
Related
Returning string state in use_effect_with_deps gives error.
use std::ops::Deref;
use yew::prelude::*;
#[hook]
pub fn use_hook_test() -> String
{
let first_load = use_state(|| true);
let hash_state = use_state(|| "".to_owned());
let hash_state_clone = hash_state.clone();
use_effect_with_deps(move |_| {
if *first_load {
wasm_bindgen_futures::spawn_local(async move {
hash_state_clone.set(format!("{:?}", "Hello"));
});
first_load.set(false);
}
|| {};
}, ());
hash_state_clone.deref().clone()
}
Error:
let hash_state_clone = hash_state.clone();
| ---------------- move occurs because `hash_state_clone` has type `yew::UseStateHandle<std::string::String>`, which does not implement the `Copy` trait
14 | use_effect_with_deps(move |_| {
| -------- value moved into closure here
...
18 | hash_state_clone.set(format!("{:?}", "Hello"));
| ---------------- variable moved due to use in closure
...
27 | hash_state_clone.deref().clone()
| ^^^^^^^^^^^^^^^^^^^^^^^^ value borrowed here after move
Here is a Yew Playground based on your example with some minor changes:
added an explicit scope to isolate the use_effect_with_deps
added a second hash_state.clone() after that scope
The result is somewhat nonsensical but compiles ok.
#[hook]
pub fn use_hook_test() -> String
{
let first_load = use_state(|| true);
let hash_state = use_state(|| "".to_owned());
{
let hash_state_clone = hash_state.clone();
use_effect_with_deps(move |_| {
if *first_load {
wasm_bindgen_futures::spawn_local(async move {
hash_state_clone.set(format!("{:?}", "Hello"));
});
first_load.set(false);
}
|| {};
}, ());
}
let hash_state_clone = hash_state.clone();
hash_state_clone.deref().clone()
}
I'm using axum and this code (found here) to download files:
use axum::{
body::StreamBody,
http::{header, StatusCode},
response::{Headers, IntoResponse},
routing::get,
Router,
};
use std::net::SocketAddr;
use tokio_util::io::ReaderStream;
#[tokio::main]
async fn main() {
let app = Router::new().route("/", get(handler));
let addr = SocketAddr::from(([127, 0, 0, 1], 3000));
axum::Server::bind(&addr)
.serve(app.into_make_service())
.await
.unwrap();
}
async fn handler() -> impl IntoResponse {
// `File` implements `AsyncRead`
let file = match tokio::fs::File::open("Cargo.toml").await {
Ok(file) => file,
Err(err) => return Err((StatusCode::NOT_FOUND, format!("File not found: {}", err))),
};
// convert the `AsyncRead` into a `Stream`
let stream = ReaderStream::new(file);
// convert the `Stream` into an `axum::body::HttpBody`
let body = StreamBody::new(stream);
let headers = Headers([
(header::CONTENT_TYPE, "text/toml; charset=utf-8"),
]);
Ok((headers, body))
}
Everything works. But I cannot find a way to move the below code in a separate function:
let file = match tokio::fs::File::open("Cargo.toml").await {
Ok(file) => file,
Err(err) => return Err((StatusCode::NOT_FOUND, format!("File not found: {}", err))),
};
I would like to use both tokio::fs::File and https://crates.io/crates/rust-s3 methods in this function.
So I need a "common type" which appear to be AsyncRead, I think.
What should be the signature of the function?
I tried with:
use tokio::io::AsyncRead;
pub struct Player {
db: Arc<DB>
}
impl Handler {
pub async fn player_pdf(
&self,
id: &str,
) -> Result<&(dyn AsyncRead)> {
//...use id here...
let file = &tokio::fs::File::open("player.pdf").await?;
Ok(file)
}
}
but I get the error:
error[E0308]: mismatched types
|
55 | Ok(file)
| -- ^^^^
| | |
| | expected reference, found struct `tokio::fs::File`
| | help: consider borrowing here: `&file`
| arguments to this enum variant are incorrect
|
= note: expected reference `&dyn tokio::io::AsyncRead`
found struct `tokio::fs::File`
I tried with: let file = &tokio::fs::File::open("player.pdf").await?; and I got:
error[E0515]: cannot return value referencing temporary value
|
43 | let file = &tokio::fs::File::open(...
| --------------------------- temporary value created here
...
55 | Ok(file)
| ^^^^^^^^ returns a value referencing data owned by the current function
What can I use?
Returning a generic "boxed" value might be the solution here:
impl Handler {
pub async fn player_pdf(
&self,
id: &str,
) -> Result<Box<dyn AsyncRead>> {
//...use id here...
Ok(Box::new(tokio::fs::File::open("player.pdf").await?))
}
}
Where now there's no dangling reference, it's encapsulated and fully owned.
I'm trying to use a Mutex<Sender> inside an async closure but I'm not entirely sure why I'm getting the error below:
error: lifetime may not live long enough
--> src/main.rs:120:41
|
120 | io.add_method(MARK_ITSELF, move |_| async {
| ________________________________--------_^
| | | |
| | | return type of closure `impl std::future::Future<Output = Result<jsonrpc::serde_json::Value, jsonrpc_http_server::jsonrpc_core::Error>>` contains a lifetime `'2`
| | lifetime `'1` represents this closure's body
121 | | trace!("Mark itself!");
122 | | let tx = sender.lock().map_err(to_internal)?;
123 | | tx.send(Action::MarkItself)
124 | | .map_err(to_internal)
125 | | .map(|_| Value::Bool(true))
126 | | });
| |_____^ returning this value requires that `'1` must outlive `'2`
|
= note: closure implements `Fn`, so references to captured variables can't escape the closure
My main function looks like this:
use jsonrpc::serde_json::Value;
use jsonrpc::Error as ClientError;
use jsonrpc::{
serde_json::value::RawValue,
simple_http::{self, SimpleHttpTransport},
Client,
};
use jsonrpc_http_server::jsonrpc_core::{Error as ServerError, IoHandler};
use jsonrpc_http_server::ServerBuilder;
use log::{debug, error, trace};
use serde::Deserialize;
use std::rc::Rc;
use std::sync::mpsc::Receiver;
use std::sync::Mutex;
use std::thread;
use std::{
env, fmt,
net::SocketAddr,
sync::mpsc::{channel, Sender},
};
const START_ROLL_CALL: &str = "start_roll_call";
const MARK_ITSELF: &str = "mark_itself";
fn create_client(url: &str, user: &str, pass: &str) -> Result<Client, simple_http::Error> {
let t = SimpleHttpTransport::builder()
.url(url)?
.auth(user, Some(pass))
.build();
Ok(Client::with_transport(t))
}
fn spawn_worker() -> Result<Sender<Action>, failure::Error> {
let (tx, rx): (Sender<Action>, Receiver<Action>) = channel();
let next: SocketAddr = env::var("NEXT")?.parse()?;
thread::spawn(move || {
let remote = Remote::new(next).unwrap();
let mut in_roll_call = false;
for action in rx.iter() {
match action {
Action::StartRollCall => {
if !in_roll_call {
if remote.start_roll_call().is_ok() {
debug!("ON");
in_roll_call = true;
}
} else {
if remote.mark_itself().is_ok() {
debug!("OFF");
in_roll_call = false;
}
}
}
Action::MarkItself => {
if in_roll_call {
if remote.mark_itself().is_ok() {
debug!("OFF");
in_roll_call = false;
}
} else {
debug!("SKIP");
}
}
}
}
});
Ok(tx)
}
enum Action {
StartRollCall,
MarkItself,
}
struct Remote {
client: Client,
}
impl Remote {
fn new(addr: SocketAddr) -> Result<Self, simple_http::Error> {
let url = format!("http://{}", addr);
let client = create_client(&url, "", "")?;
Ok(Self { client })
}
fn call_method<T>(&self, method: &str, params: &[Box<RawValue>]) -> Result<T, ClientError>
where
T: for<'de> Deserialize<'de>,
{
let request = self.client.build_request(method, params);
self.client
.send_request(request)
.and_then(|res| res.result::<T>())
}
fn start_roll_call(&self) -> Result<bool, ClientError> {
self.call_method(START_ROLL_CALL, &[])
}
fn mark_itself(&self) -> Result<bool, ClientError> {
self.call_method(MARK_ITSELF, &[])
}
}
fn main() -> Result<(), failure::Error> {
env_logger::init();
let tx = spawn_worker()?;
let addr: SocketAddr = env::var("ADDRESS")?.parse()?;
let mut io = IoHandler::default();
let sender = Mutex::new(tx.clone());
io.add_method(START_ROLL_CALL, move |_| async move {
trace!("Starting roll call!");
let tx = sender.lock().map_err(to_internal)?;
tx.send(Action::StartRollCall)
.map_err(to_internal)
.map(|_| Value::Bool(true))
});
let sender = Mutex::new(tx.clone());
io.add_method(MARK_ITSELF, move |_| async {
trace!("Mark itself!");
let tx = sender.lock().map_err(to_internal)?;
tx.send(Action::MarkItself)
.map_err(to_internal)
.map(|_| Value::Bool(true))
});
let server = ServerBuilder::new(io).start_http(&addr)?;
Ok(server.wait())
}
fn to_internal<E: fmt::Display>(err: E) -> ServerError {
error!("Error: {}", err);
ServerError::internal_error()
}
The main idea is to pass the mspc sender to the closure so that the method can send the Action(An enum). Is there something I'm doing wrong?
The problem is add_method requires that
your closure is static, and
the Future returned from your closure is static.
Try this
let sender = Arc::new(Mutex::new(tx.clone()));
io.add_method(START_ROLL_CALL, move |_| {
let cloned_sender = sender.clone();
async move {
trace!("Starting roll call!");
let tx = cloned_sender.lock().map_err(to_internal)?;
tx.send(Action::StartRollCall)
.map_err(to_internal)
.map(|_| Value::Bool(true))
}
});
Side note: you are using sync Mutex in an async environment. This undermines the benefits of async. Consider using async Mutex such as Tokio Mutex or async-lock Mutex.
I'm trying to write an async function that will traverse the filesystem tree, recursively, and calls an asynchronous callback for each file found.
This is for a learning effort, I have no real use case.
Here is what I have so far:
use async_std::{
fs::{self, *},
path::*,
prelude::*,
}; // 1.5.0, features = ["unstable"]
use futures::{
executor::block_on,
future::{BoxFuture, FutureExt},
}; // 0.3.4
use std::{marker::Sync, pin::Pin};
fn main() {
fn walkdir<F>(path: String, cb: &'static F) -> BoxFuture<'static, ()>
where
F: Fn(&DirEntry) -> BoxFuture<()> + Sync + Send,
{
async move {
let mut entries = fs::read_dir(&path).await.unwrap();
while let Some(path) = entries.next().await {
let entry = path.unwrap();
let path = entry.path().to_str().unwrap().to_string();
if entry.path().is_file().await {
cb(&entry).await
} else {
walkdir(path, cb).await
}
}
}
.boxed()
}
let foo = async {
walkdir(".".to_string(), &|entry: &DirEntry| async {
async_std::println!(">> {}\n", &entry.path().to_str().unwrap()).await
})
.await
};
block_on(foo);
}
I get this far by some sort of trial and error, but now I'm stuck on async closure callback with this error
warning: unused import: `path::*`
--> src/main.rs:3:5
|
3 | path::*,
| ^^^^^^^
|
= note: `#[warn(unused_imports)]` on by default
warning: unused import: `pin::Pin`
--> src/main.rs:10:25
|
10 | use std::{marker::Sync, pin::Pin};
| ^^^^^^^^
error[E0308]: mismatched types
--> src/main.rs:33:54
|
33 | walkdir(".".to_string(), &|entry: &DirEntry| async {
| ______________________________________________________^
34 | | async_std::println!(">> {}\n", &entry.path().to_str().unwrap()).await
35 | | })
| |_________^ expected struct `std::pin::Pin`, found opaque type
|
= note: expected struct `std::pin::Pin<std::boxed::Box<dyn core::future::future::Future<Output = ()> + std::marker::Send>>`
found opaque type `impl core::future::future::Future`
use async_std::{
fs::{self, *},
path::*,
prelude::*,
}; // 1.5.0
use futures::{future::{Future, FutureExt, LocalBoxFuture}, executor}; // 0.3.4
fn main() {
async fn walkdir<R>(path: impl AsRef<Path>, mut cb: impl FnMut(DirEntry) -> R)
where
R: Future<Output = ()>,
{
fn walkdir_inner<'a, R>(path: &'a Path, cb: &'a mut dyn FnMut(DirEntry) -> R) -> LocalBoxFuture<'a, ()>
where
R: Future<Output = ()>,
{
async move {
let mut entries = fs::read_dir(path).await.unwrap();
while let Some(path) = entries.next().await {
let entry = path.unwrap();
let path = entry.path();
if path.is_file().await {
cb(entry).await
} else {
walkdir_inner(&path, cb).await
}
}
}.boxed_local()
}
walkdir_inner(path.as_ref(), &mut cb).await
}
executor::block_on({
walkdir(".", |entry| async move {
async_std::println!(">> {}", entry.path().display()).await
})
});
}
Notable changes:
Take in AsRef<Path> instead of a String and a generic closure instead of a trait object reference
Change the closure type to be FnMut as it's more permissive
The closure returns any type that is a future.
There's an inner implementation function that hides the ugly API required for recursive async functions.
The callback takes the DirEntry by value instead of by reference.
See also:
How to asynchronously explore a directory and its sub-directories?
How to using async fn callback in rust
I'm trying to use the code I found here with some problems, basically it's a borrowing error using some macros, the error:
Compiling playground v0.0.1 (file:///playground)
error[E0597]: `body` does not live long enough
--> src/main.rs:12:3
|
6 | let raw_structure = borrow_function(&body);
| ---- borrow occurs here
...
12 | }
| ^ `body` dropped here while still borrowed
...
31 | let body = get_body_as!(&str, "Hello", function1);
| -------------------------------------- in this macro invocation
32 | println!("Hello");
33 | }
| - borrowed value needs to live until here
I manage to create a Minimal, Complete, and Verifiable example, I was thinking that a solution would be to transform the macros into functions, but I'm not completely sure how to do that either (Playground
):
macro_rules! get_body_as {
($structure:ty, $req:expr, $error_fn:ident) => {
{
let body = get_body!($req, $error_fn);
let raw_structure = borrow_function(&body);
match raw_structure {
Ok(structure) => structure,
Err(error) => "Error"
}
}
}
}
macro_rules! get_body {
($req:expr, $error_fn:ident) => {
{
let mut payload = String::new();
payload
}
}
}
fn borrow_function(s: &str) -> Result<&str, &str> {
Ok(s)
}
fn main() {
let function1 = |s: &str| s;
let body = get_body_as!(&str, "Hello", function1);
println!("Hello");
}
The problem is that you are trying to return a reference to a body variable from a block which owns the body variable, but body is to be dropped at the end of that block, so the reference would outlive the data it references.
If you want your example to compile, you can alter your code so that body is declared within the main function using ident parameter added to get_body_as macro:
macro_rules! get_body_as {
($structure:ty, $req:expr, $error_fn:ident, $body: ident) => {
let $body = get_body!($req, $error_fn);
let raw_structure = borrow_function(&$body);
match raw_structure {
Ok(structure) => structure,
Err(error) => "Error"
}
}
}
macro_rules! get_body {
($req:expr, $error_fn:ident) => {
{
let mut payload = String::new();
payload
}
}
}
fn borrow_function(s: &str) -> Result<&str, &str> {
Ok(s)
}
fn main() {
let function1 = |s: &str| s;
get_body_as!(&str, "Hello", function1, body);
println!("Hello");
}
This example compiles, but still has warnings about unused variables, I have made only minimal changes for compilation to succeed.