Fill a string buffer from a thread [duplicate] - rust

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How do I share a mutable object between threads using Arc?
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Lifetime troubles sharing references between threads
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With hyper, I need to make an HTTP connection and read the results.
I want to wrap the whole thing in a timeout,
so I start a thread
and use recv_timeout to wait for it.
Wrapping just the send works,
but I want to also wrap read_to_string.
Here is the code:
fn send_request(url: &str) -> Result<Response, MyAppError> {
let mut c = Client::new();
let mut req = c.get(url);
req.send().map_err(|e| MyAppError::TcpError(e))
}
fn get_url(url: &str, mut buf: &mut String) -> Result<u16, MyAppError> {
let mut resp = send_request(url)?;
resp.read_to_string(&mut buf).map_err(|e| MyAppError::ReadError(e))?;
Ok(resp.status.to_u16())
}
fn get_url_with_timeout_2(url: &str, mut buf: &mut String) -> Result<u16, MyAppError> {
let (tx, rx) = mpsc::channel();
let url = url.to_owned();
let t = thread::spawn(move || {
match tx.send(get_url(&url, &mut buf)) {
Ok(()) => {} // everything good
Err(_) => {} // we have been released, no biggie
}
});
match rx.recv_timeout(Duration::from_millis(5000)) {
Ok(resp) => resp,
Err(_) => Err(MyAppError::Timeout),
}
}
Unfortunately I get a compiler error:
error[E0477]: the type `[closure#src/main.rs:53:25: 58:4 tx:std::sync::mpsc::Sender<std::result::Result<u16, MyAppError>>, url:std::string::String, buf:&mut std::string::String]` does not fulfill the required lifetime
--> src/main.rs:53:11
|
53 | let t = thread::spawn(move || {
| ^^^^^^^^^^^^^
|
= note: type must outlive the static lifetime
How can I pass the buffer to the thread,
let it fill it,
and then print out the buffer back on the main thread?
(This is Rust 1.15.1.)
This repository gives a complete main.rs and shows three examples for getting the webpage:
With no timeout.
With a timeout just on send.
With a timeout on the whole thing.
If you take out 3, it all compiles and runs.
What can I change about 3 to make that work too?
By the way, making a web request is really just the "occasion" for this question. I've already seen this question about doing a timeout. My own interest is not the timeout per se, but about how to fill up a buffer on one thread and read it on another.
Share mutable object between threads suggests using Arc and Mutex to safely share data between threads. Here is an attempt at that:
fn get_url_with_timeout_3(url: &str) -> Result<(u16, String), MyAppError> {
let (tx, rx) = mpsc::channel();
let url = url.to_owned();
let shbuf = Arc::new(Mutex::new(String::new()));
let shbuf2 = shbuf.clone();
let t = thread::spawn(move || {
let mut c = Client::new();
let mut req = c.get(&url);
let mut ret = match req.send() {
Ok(mut resp) => {
let mut buf2 = shbuf2.lock().unwrap();
match resp.read_to_string(&mut buf2) {
Ok(_) => Ok(resp.status.to_u16()),
Err(e) => Err(MyAppError::ReadError(e)),
}
}
Err(e) => Err(MyAppError::TcpError(e)),
};
match tx.send(ret) {
Ok(()) => {} // everything good
Err(_) => {} // we have been released, no biggie
}
});
match rx.recv_timeout(Duration::from_millis(5000)) {
Ok(maybe_status_code) => {
let buf2 = shbuf.lock().unwrap();
Ok((maybe_status_code?, *buf2))
}
Err(_) => Err(MyAppError::Timeout),
}
}
This gives me the error cannot move out of borrowed content for trying to return *buf2 (which makes sense, since it would be leaking data out of the Mutex), but I'm not sure how to express this in a structure where Rust can see the pattern.
If the request thread times out, it holds the lock forever — but I never try to read the buffer, so who cares. If the request thread finishes, it releases the lock and goes away, and the main thread will hold the only reference. I can reason that it is safe, but I'm not sure how to convince the compiler.
I'm not allowed to answer this question since it is supposedly a duplicate, but I've added 3 working implementations to my GitHub repository using the ideas from the comments.