Add code examples

Author: rustkas

code/spawn-blocking-workspace/Cargo.toml

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+workspace = { members = ["members/spawn-blocking-lib"] }
+[package]
+name = "spawn-blocking-workspace"
+version = "0.1.0"
+edition = "2021"
+
+# See more keys and their definitions at https://doc.rust-lang.org/cargo/reference/manifest.html
+
+[dependencies]

code/spawn-blocking-workspace/members/spawn-blocking-lib/Cargo.toml

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+[package]
+name = "spawn-blocking-lib"
+version = "0.1.0"
+edition = "2021"
+
+# See more keys and their definitions at https://doc.rust-lang.org/cargo/reference/manifest.html
+
+[dependencies]
+
+async-std = "1.7"

code/spawn-blocking-workspace/members/spawn-blocking-lib/src/lib.rs

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+use std::sync::{Arc, Mutex};
+use std::task::Waker;
+
+pub struct SpawnBlocking<T>(Arc<Mutex<Shared<T>>>);
+
+struct Shared<T> {
+    value: Option<T>,
+    waker: Option<Waker>,
+}
+
+pub fn spawn_blocking<T, F>(closure: F) -> SpawnBlocking<T>
+where F: FnOnce() -> T,
+      F: Send + 'static,
+      T: Send + 'static,
+{
+    let inner = Arc::new(Mutex::new(Shared {
+        value: None,
+        waker: None,
+    }));
+
+    std::thread::spawn({
+        let inner = inner.clone();
+        move || {
+            let value = closure();
+
+            let maybe_waker = {
+                let mut guard = inner.lock().unwrap();
+                guard.value = Some(value);
+                guard.waker.take()
+            };
+
+            if let Some(waker) = maybe_waker {
+                waker.wake();
+            }
+        }
+    });
+
+    SpawnBlocking(inner)
+}
+
+use std::future::Future;
+use std::pin::Pin;
+use std::task::{Context, Poll};
+
+impl<T: Send> Future for SpawnBlocking<T> {
+    type Output = T;
+
+    fn poll(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<T> {
+        let mut guard = self.0.lock().unwrap();
+        if let Some(value) = guard.value.take() {
+            return Poll::Ready(value);
+        }
+
+        guard.waker = Some(cx.waker().clone());
+        Poll::Pending
+    }
+}

code/spawn-blocking-workspace/src/main.rs

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+fn main() {
+    println!("Hello, world!");
+}