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Martin Hope
goose_lake
Asked: 2024-11-28 22:58:37 +0800 CST
  • 5

我正在考虑将拥有一些线程安全值的闭包传递给生成的线程的可能性。然后该线程将能够仅通过知道签名来调用某些东西，而其内容对它来说是不透明的。

我写了一个简单的测试，令人惊讶的是，它成功了。为了使闭包可以在线程内调用，Rust 编译器建议为其添加std::marker::Send和'static约束。第一个适用是有道理的——闭包捕获的所有值都是Send，但静态生命周期要求被认为已满足，这让我很困惑，因为我假设编译器会认为闭包及其拥有的值具有特定的非静态生命周期。

我想了解原因。代码如下：

use std::sync::{mpsc::{Receiver, Sender}, Arc, Mutex};

fn main() {
    let tx = start_thread();

    // can also run in a loop with a sleep in between or whatever
    let _ = tx.send(String::from("Something"));
}

fn start_thread() -> Sender<String> {
    // Something created on the main thread that we pass to the spawned thread
    //  inside the closure -- the spawned thread has no direct knowledge of it 
    let closure_owned_value: Arc<Mutex<f32>> = Arc::new(Mutex::new(42.0));
    
    // A closure we want to be called by the spawned thread, 
    // but not defined there -- this is considered 'static somehow?
    let on_thread_callback = move |msg: String| {
        println!("Got back message from thread: {:?}, owned value: {:?}", msg, closure_owned_value);
    };

    let (tx, rx) = std::sync::mpsc::channel();

    spawn_thread_with_callback(rx, on_thread_callback);

    tx
}

fn spawn_thread_with_callback<F>(
    rx: Receiver<String>,
    callback: F
) -> std::thread::JoinHandle<()>
where
    F: Fn(String) -> () + std::marker::Send + 'static
{
    std::thread::spawn(move || {
        /* Run an infinite loop as long as channel is open. */
        while let Ok(message) = rx.recv() {
            println!("Thread received message: {:?}", message);
            callback(String::from("Hello back from thread!"));
        }
    })
}
multithreading
Martin Hope
goose_lake
Asked: 2024-11-12 21:18:39 +0800 CST
  • 6

我收到一个很大的字符串化 JSON 对象，其中包含多个字段，其中一些字段很大。例如，假设该对象如下所示：

{
  "somethingHuge": (200 000 character string)
  "relevantField": true
}

我只对感兴趣relevantField，所以为了节省性能，我不想解析somethingHuge，分配内存来保存该字符串等。解析时可以跳过该字段吗？

注意：物体的形状是由外界因素决定的，无法仅接收相关数据。

javascript