Custom Waker-Driven Future Implementation

use std::future::Future;
use std::pin::Pin;
use std::sync::atomic::{AtomicBool, Ordering};
use std::sync::Arc;
use std::task::{Context, Poll, Waker};
 
pub struct SignalFuture {
    state: Arc<SignalState>,
}
 
struct SignalState {
    completed: AtomicBool,
    waker: std::sync::Mutex<Option<Waker>>,
}
 
impl Future for SignalFuture {
    type Output = &'static str;
 
    fn poll(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Self::Output> {
        if self.state.completed.load(Ordering::Acquire) {
            Poll::Ready("Signal received")
        } else {
            let mut waker_guard = self.state.waker.lock().unwrap();
            *waker_guard = Some(cx.waker().clone());
            Poll::Pending
        }
    }
}