feat: add mini tokio

__concurrent/async_study/Cargo.lock

@@ -7,6 +7,7 @@ name = "async_study"
 version = "0.1.0"
 dependencies = [
  "bytes",
+ "futures",
  "futures-util",
  "tokio",
 ]
@@ -29,12 +30,71 @@ version = "1.0.0"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "baf1de4339761588bc0619e3cbc0120ee582ebb74b53b4efbf79117bd2da40fd"
 
+[[package]]
+name = "futures"
+version = "0.3.21"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "f73fe65f54d1e12b726f517d3e2135ca3125a437b6d998caf1962961f7172d9e"
+dependencies = [
+ "futures-channel",
+ "futures-core",
+ "futures-executor",
+ "futures-io",
+ "futures-sink",
+ "futures-task",
+ "futures-util",
+]
+
+[[package]]
+name = "futures-channel"
+version = "0.3.21"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "c3083ce4b914124575708913bca19bfe887522d6e2e6d0952943f5eac4a74010"
+dependencies = [
+ "futures-core",
+ "futures-sink",
+]
+
 [[package]]
 name = "futures-core"
 version = "0.3.21"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "0c09fd04b7e4073ac7156a9539b57a484a8ea920f79c7c675d05d289ab6110d3"
 
+[[package]]
+name = "futures-executor"
+version = "0.3.21"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "9420b90cfa29e327d0429f19be13e7ddb68fa1cccb09d65e5706b8c7a749b8a6"
+dependencies = [
+ "futures-core",
+ "futures-task",
+ "futures-util",
+]
+
+[[package]]
+name = "futures-io"
+version = "0.3.21"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "fc4045962a5a5e935ee2fdedaa4e08284547402885ab326734432bed5d12966b"
+
+[[package]]
+name = "futures-macro"
+version = "0.3.21"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "33c1e13800337f4d4d7a316bf45a567dbcb6ffe087f16424852d97e97a91f512"
+dependencies = [
+ "proc-macro2",
+ "quote",
+ "syn",
+]
+
+[[package]]
+name = "futures-sink"
+version = "0.3.21"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "21163e139fa306126e6eedaf49ecdb4588f939600f0b1e770f4205ee4b7fa868"
+
 [[package]]
 name = "futures-task"
 version = "0.3.21"
@@ -47,10 +107,16 @@ version = "0.3.21"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "d8b7abd5d659d9b90c8cba917f6ec750a74e2dc23902ef9cd4cc8c8b22e6036a"
 dependencies = [
+ "futures-channel",
  "futures-core",
+ "futures-io",
+ "futures-macro",
+ "futures-sink",
  "futures-task",
+ "memchr",
  "pin-project-lite",
  "pin-utils",
+ "slab",
 ]
 
 [[package]]
@@ -217,6 +283,12 @@ dependencies = [
  "libc",
 ]
 
+[[package]]
+name = "slab"
+version = "0.4.5"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "9def91fd1e018fe007022791f865d0ccc9b3a0d5001e01aabb8b40e46000afb5"
+
 [[package]]
 name = "smallvec"
 version = "1.8.0"

__concurrent/async_study/Cargo.toml

@@ -9,3 +9,4 @@ edition = "2021"
 tokio = { version = "1.0", features = ["full"] }
 futures-util = { version = "0.3", default-features = false }
 bytes = "1.1"
+futures = "0.3"

__concurrent/async_study/examples/mini_tokio.rs

@@ -0,0 +1,77 @@
+use std::collections::VecDeque;
+use std::future::Future;
+use std::pin::Pin;
+use std::task::{Context, Poll};
+use std::time::{Duration, Instant};
+
+use futures::task;
+
+// from: https://tokio.rs/tokio/tutorial/async
+fn main() {
+    let mut mini_tokio = MiniTokio::new();
+
+    mini_tokio.spawn(async {
+        let when = Instant::now() + Duration::from_millis(10);
+        let future = Delay { when };
+
+        let out = future.await;
+        assert_eq!(out, "done");
+    });
+
+    mini_tokio.run();
+}
+
+struct MiniTokio {
+    tasks: VecDeque<Task>,
+}
+
+type Task = Pin<Box<dyn Future<Output=()> + Send>>;
+
+impl MiniTokio {
+    fn new() -> MiniTokio {
+        MiniTokio {
+            tasks: VecDeque::new(),
+        }
+    }
+
+    /// Spawn a future onto the mini-tokio instance.
+    fn spawn<F>(&mut self, future: F)
+        where
+            F: Future<Output=()> + Send + 'static,
+    {
+        self.tasks.push_back(Box::pin(future));
+    }
+
+    fn run(&mut self) {
+        let waker = task::noop_waker();
+        let mut cx = Context::from_waker(&waker);
+
+        while let Some(mut task) = self.tasks.pop_front() {
+            if task.as_mut().poll(&mut cx).is_pending() {
+                self.tasks.push_back(task);
+            }
+        }
+    }
+}
+
+
+struct Delay {
+    when: Instant,
+}
+
+impl Future for Delay {
+    type Output = &'static str;
+
+    fn poll(self: Pin<&mut Self>, cx: &mut Context<'_>)
+            -> Poll<&'static str>
+    {
+        if Instant::now() >= self.when {
+            println!("Hello world");
+            Poll::Ready("done")
+        } else {
+            // Ignore this line for now.
+            cx.waker().wake_by_ref();
+            Poll::Pending
+        }
+    }
+}