diff --git a/codes/reactor_executor/Cargo.lock b/codes/reactor_executor/Cargo.lock
new file mode 100644
index 0000000000000000000000000000000000000000..4254be511d9da3b724268412d8f69e315dc5d5bd
--- /dev/null
+++ b/codes/reactor_executor/Cargo.lock
@@ -0,0 +1,113 @@
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+# It is not intended for manual editing.
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+
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+]
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+ "windows_i686_gnu",
+ "windows_i686_gnullvm",
+ "windows_i686_msvc",
+ "windows_x86_64_gnu",
+ "windows_x86_64_gnullvm",
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diff --git a/codes/reactor_executor/Cargo.toml b/codes/reactor_executor/Cargo.toml
new file mode 100644
index 0000000000000000000000000000000000000000..117fa460fa78e25abd955fb3db2ec3c08ead0357
--- /dev/null
+++ b/codes/reactor_executor/Cargo.toml
@@ -0,0 +1,7 @@
+[package]
+name = "reactor_executor"
+version = "0.1.0"
+edition = "2021"
+
+[dependencies]
+mio = { version = "1.0.3", features = ["net", "os-poll"] }
diff --git a/codes/reactor_executor/src/future.rs b/codes/reactor_executor/src/future.rs
new file mode 100644
index 0000000000000000000000000000000000000000..2fe6d932dcd6d0218f382ec389b915b757e405d7
--- /dev/null
+++ b/codes/reactor_executor/src/future.rs
@@ -0,0 +1,26 @@
+use crate::runtime::Waker;
+
+// Future trait looks like standard Future except for the missing context
+// pub trait Future {
+// type Output;
+// fn poll(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Self::Output>;
+//}
+// We now also have the `Waker` as an argument of the `Future` trait. We see that in the standard
+// library the Waker is hidden in a Context which we do not need here
+pub trait Future {
+ type Output;
+
+ fn poll(&mut self, waker: &Waker) -> PollState<Self::Output>;
+}
+
+// Similar to the Poll #[derive(Debug)]
+// pub enum Poll<T> {
+// Ready(T),
+// Pending,
+// }
+pub enum PollState<T> {
+ Ready(T),
+ NotReady,
+}
+
+// Exercise adapt the join_all function to accept the Waker structs
diff --git a/codes/reactor_executor/src/http.rs b/codes/reactor_executor/src/http.rs
new file mode 100644
index 0000000000000000000000000000000000000000..58cc23e717426772be7a38d71b26bd154769e8cc
--- /dev/null
+++ b/codes/reactor_executor/src/http.rs
@@ -0,0 +1,122 @@
+use mio::Interest;
+
+use crate::future::{Future, PollState};
+use crate::runtime::{self, reactor, Waker};
+use std::io::{ErrorKind, Read, Write};
+
+// Simple helper function to write GET requests
+fn get_req(path: &str) -> String {
+ format!(
+ "GET {path} HTTP/1.1\r\n\
+ Host: localhost\r\n\
+ Connection: close\r\n\
+ \r\n"
+ )
+}
+
+pub struct Http;
+
+impl Http {
+ pub fn get(path: &str) -> impl Future<Output = String> {
+ HttpGetFuture::new(path)
+ }
+}
+
+// The id of the `Future` is also a needed information to register it for the `Waker` and `Poll`
+struct HttpGetFuture {
+ // Option since we will not conect upon creation
+ stream: Option<mio::net::TcpStream>,
+ // buffer to read from the TcpStream
+ buffer: Vec<u8>,
+ // The GET request we will construct
+ path: String,
+ // The id of our Future
+ id: usize,
+}
+
+impl HttpGetFuture {
+ // Create the new HttpGetFuture with default state
+ // We increment the `next_id()` and assign it to the id field
+ fn new(path: &str) -> Self {
+ let id = reactor().next_id();
+ Self {
+ stream: None,
+ buffer: vec![],
+ path: String::from(path),
+ id,
+ }
+ }
+
+ // Writes the request to a non bocking stream. Here we are using mio t connect to the socket
+ // We just create the stream and do not perform any request here
+ fn write_request(&mut self) {
+ let stream = std::net::TcpStream::connect("localhost:8080").unwrap();
+ stream.set_nonblocking(true).unwrap();
+ let mut stream = mio::net::TcpStream::from_std(stream);
+ stream.write_all(get_req(&self.path).as_bytes()).unwrap();
+ self.stream = Some(stream);
+ }
+}
+
+impl Future for HttpGetFuture {
+ type Output = String;
+
+ // We have three different states here:
+ // 1. stream is None, therefore we have not started executing anything (State would be
+ // NotStarted)
+ // 2. stream is Some and read returns WouldBlock (State would be Pending)
+ // 3. stream is Some and read returns 0 (State would be Resolved)
+ // These states are implicit here but we actually have some kind of state machine
+ fn poll(&mut self, waker: &Waker) -> PollState<Self::Output> {
+ // First poll we write the GET request to the server and register our interest into read
+ // evnts on te TcpStream. We then directly poll the stream immediatly (instead of returning
+ // NotReady).
+ //
+ // It is very important to note that we call poll() at least once before doing anything so
+ // we actually start doing something not when we create the future but when we await it
+ // This is an example of Lazy evaluation (we only do something when we poll not before)
+ if self.stream.is_none() {
+ println!("First poll - start operation");
+ self.write_request();
+ // Registering the Tcp stream as a source of events in the poll instance
+ runtime::reactor().register(self.stream.as_mut().unwrap(), Interest::READABLE, self.id);
+ // We also set the `Waker` responsible for handling the `Future`
+ runtime::reactor().set_waker(waker, self.id);
+ }
+ let mut buf = vec![0u8; 4096];
+ // We loop until everything is read and return Ready when done
+ loop {
+ // We listen on the socket and read
+ match self.stream.as_mut().unwrap().read(&mut buf) {
+ // 0 bytes read so we are finished we got the entire GET response
+ Ok(0) => {
+ let s = String::from_utf8_lossy(&self.buffer);
+ // The future is over we deregister our interest from this source of events for
+ // the current id
+ runtime::reactor().deregister(self.stream.as_mut().unwrap(), self.id);
+ break PollState::Ready(String::from(s));
+ }
+ // We read n bytes so we continue reading
+ Ok(n) => {
+ self.buffer.extend(&buf[0..n]);
+ continue;
+ }
+ // This error indicates that the data is not ready yet or that that there is more
+ // data we did not received yet
+ Err(e) if e.kind() == ErrorKind::WouldBlock => {
+ println!("Data not ready");
+ // We need to
+ runtime::reactor().set_waker(waker, self.id);
+ break PollState::NotReady;
+ }
+ // This error can happen if a signal interrupted the read (which can happen) we
+ // handle this case by reading again
+ Err(e) if e.kind() == ErrorKind::Interrupted => {
+ continue;
+ }
+ // Nothing we can do. We panic!
+ Err(e) => panic!("{e:?}"),
+ }
+ }
+ }
+}
diff --git a/codes/reactor_executor/src/main.rs b/codes/reactor_executor/src/main.rs
new file mode 100644
index 0000000000000000000000000000000000000000..09f117796061659a9e37a9f04c2618e7cdaecc5e
--- /dev/null
+++ b/codes/reactor_executor/src/main.rs
@@ -0,0 +1,73 @@
+mod future;
+mod http;
+mod runtime;
+
+use future::{Future, PollState};
+use http::Http;
+use runtime::Waker;
+
+fn main() {
+ let mut executor = runtime::init();
+ executor.block_on(async_main());
+}
+
+fn async_main() -> impl Future<Output = String> {
+ Coroutine::new()
+}
+
+enum State {
+ Start,
+ Wait1(Box<dyn Future<Output = String>>),
+ Wait2(Box<dyn Future<Output = String>>),
+ Resolved,
+}
+
+struct Coroutine {
+ state: State,
+}
+
+impl Coroutine {
+ fn new() -> Self {
+ Self {
+ state: State::Start,
+ }
+ }
+}
+
+// We need to adapt `poll()` and the subsequent calls of the children `Future` to have an extra
+// argument: the `Waker`.
+impl Future for Coroutine {
+ type Output = String;
+
+ fn poll(&mut self, waker: &Waker) -> PollState<Self::Output> {
+ loop {
+ match self.state {
+ State::Start => {
+ println!("Program starting");
+ let fut1 = Box::new(Http::get("/600/HelloAsyncAwait"));
+ self.state = State::Wait1(fut1);
+ }
+
+ State::Wait1(ref mut future) => match future.poll(waker) {
+ PollState::Ready(txt) => {
+ println!("{txt}");
+ let fut2 = Box::new(Http::get("/400/HelloAsyncAwait"));
+ self.state = State::Wait2(fut2);
+ }
+ PollState::NotReady => break PollState::NotReady,
+ },
+
+ State::Wait2(ref mut future) => match future.poll(waker) {
+ PollState::Ready(txt) => {
+ println!("{txt}");
+ self.state = State::Resolved;
+ break PollState::Ready(String::new());
+ }
+ PollState::NotReady => break PollState::NotReady,
+ },
+
+ State::Resolved => panic!("Polled a resolved future"),
+ }
+ }
+ }
+}
diff --git a/codes/reactor_executor/src/runtime.rs b/codes/reactor_executor/src/runtime.rs
new file mode 100644
index 0000000000000000000000000000000000000000..e87aed2a804a8ce64b68fd5970ba77a04ceb3843
--- /dev/null
+++ b/codes/reactor_executor/src/runtime.rs
@@ -0,0 +1,10 @@
+mod executor;
+mod reactor;
+
+pub use executor::{Executor, Waker};
+pub use reactor::reactor;
+
+pub fn init() -> Executor {
+ reactor::start();
+ Executor::new()
+}
diff --git a/codes/reactor_executor/src/runtime/executor.rs b/codes/reactor_executor/src/runtime/executor.rs
new file mode 100644
index 0000000000000000000000000000000000000000..12f8a344f5abddf538aafd7dea931ed553964899
--- /dev/null
+++ b/codes/reactor_executor/src/runtime/executor.rs
@@ -0,0 +1,186 @@
+use std::{
+ cell::{Cell, RefCell},
+ collections::HashMap,
+ sync::{Arc, Mutex},
+ thread::{self, Thread},
+};
+
+use crate::future::{Future, PollState};
+
+// A `Waker` contains the thread, `std::thread::Thread`,
+// from (`thread::current()`) which it is called in order to be `park()` or `unpark()`. This
+// is not a robust method, as `park()` or `unpark()` could be called from several
+// places in the code, resulting in potential deadlocks. We will use this
+// method to ask the OS to wake up a thread at the right moment (or to put it to sleep).
+// To be really generic, we should have a `Waker` feature, but that would be too
+// complicated in the scope of this course.
+//
+// A waker contains its thread, an `id` which identifies the associated task, and a list of
+// of task identifiers that are ready to be executed. This is necessary to add
+// the current identifier to the list of tasks to be executed
+#[derive(Clone)]
+pub struct Waker {
+ thread: Thread,
+ id: usize,
+ ready_queue: Arc<Mutex<Vec<usize>>>,
+}
+
+impl Waker {
+ // Wake means add the id of the task to the ready_queue and `unpark()` the associated thread.
+ // We can then call `poll()` on the task to see its progress.
+ // Of course we must lock the ready_queue first otherwise there may be a place where we are
+ // modifying concurrently the ready_queue which would cause a concurrent access
+ pub fn wake(&self) {
+ self.ready_queue
+ .lock()
+ .map(|mut queue| queue.push(self.id))
+ .unwrap();
+ self.thread.unpark();
+ }
+}
+
+// A Task is just something that implements the `Future` trait
+type Task = Box<dyn Future<Output = String>>;
+
+// CURRENT_EXECUTOR is a static variable that is unique to the thread it was called from. It can
+// not be accessed from any other thread
+thread_local! {
+ static CURRENT_EXECUTOR: ExecutorCore = ExecutorCore::default();
+}
+
+// The `ExecutorCore` holds the state of the `Executor`.
+//
+// The `tasks` is a `HashMap` between its `id` and the actual `Taksk` (anything that implements the
+// `Future` trait). We only need a RefCell since it will never be accessed by different threads.
+// A `RefCell` allow **interior** mutability (the thing stored inside can be mutated) but rules are
+// checked at runtime instead of at compile time. Only one instance can hold a mutable reference at
+// any given time (no need for Arc). `RefCell` allows to access a value by &mut T
+//
+// The `ready_queue` is the same as the queue for the `Waker`. It contains the list of tasks ready
+// for execution. Each `Waker` having a copy and each `Waker` being on a different thread an
+// `Arc<Mutex<_>>` of the ids is necessary here.
+//
+// The `next_id` is a counter giving us the top level id of each `Future` that is spawned. It is a
+// simple `Cell` because the value inside will be replaced everything we need to mutate it. `Cell`
+// does not allow to access a `&mut T` but we need to take the value out of the `Cell` and replace
+// it wil something else.
+#[derive(Default)]
+struct ExecutorCore {
+ tasks: RefCell<HashMap<usize, Task>>,
+ ready_queue: Arc<Mutex<Vec<usize>>>,
+ next_id: Cell<usize>,
+}
+
+// The `spawn` function does the following things:
+// 1. Gets the next available id for our top level `Future`
+// 2. Adds the id and the future, into our tasks HashMap
+// 3. Adds the id into the list of ids that are ready to be executes (this would be their first
+// executrion)
+// 4. Prepares the next id (by incrementation by 1)
+//
+// Here `F` must have a 'static lifetime which means that the `Future` must live until the end of
+// our program. In other terms it must outlive `spawn()`
+pub fn spawn<F>(future: F)
+where
+ F: Future<Output = String> + 'static,
+{
+ CURRENT_EXECUTOR.with(|e| {
+ let id = e.next_id.get();
+ e.tasks.borrow_mut().insert(id, Box::new(future));
+ e.ready_queue
+ .lock()
+ .map(|mut queue| queue.push(id))
+ .unwrap();
+ e.next_id.set(id + 1);
+ });
+}
+
+// The executor is all stored in tthe `ExecutorCore` which is a local static variable anyway, so we
+// just create an empty streuct for a namespacing purpose
+pub struct Executor;
+
+impl Executor {
+ // Just a new instance, since everything is done in the CURRENT_EXECUTOR static variable when a
+ // new thread is spawned
+ pub fn new() -> Self {
+ Self {}
+ }
+
+ // Pops an id from the ready_queue list. Must of course be locked before doing anything. The
+ // queue works rather as a stack than as a queue but it's not very important.
+ fn pop_ready(&self) -> Option<usize> {
+ CURRENT_EXECUTOR.with(|e| e.ready_queue.lock().map(|mut queue| queue.pop()).unwrap())
+ }
+
+ // Returns the task that is related to the id and removes it from the tasks hashmap
+ // This will be used for polling. If the task returns not ready we will have to put it back
+ // again later
+ fn get_future(&self, id: usize) -> Option<Task> {
+ CURRENT_EXECUTOR.with(|e| e.tasks.borrow_mut().remove(&id))
+ }
+
+ // Creates a new Waker from an id
+ fn get_waker(&self, id: usize) -> Waker {
+ Waker {
+ id,
+ thread: thread::current(),
+ ready_queue: CURRENT_EXECUTOR.with(|e| e.ready_queue.clone()),
+ }
+ }
+
+ // Inserts a new task with a given id into the tasks HashMap
+ fn insert_task(&self, id: usize, task: Task) {
+ CURRENT_EXECUTOR.with(|e| e.tasks.borrow_mut().insert(id, task));
+ }
+
+ // Counts how many tasks are left to be executed
+ fn task_count(&self) -> usize {
+ CURRENT_EXECUTOR.with(|e| e.tasks.borrow().len())
+ }
+
+ // The entry point of our `Executor`. We pass the top level `Future` which can then spawn
+ // whetever `Future` it wants into the `Executor`.
+ //
+ // What block_on() does is the following:
+ //
+ // 1. Spawn the `Future` passed as an argument
+ // 2. We loop until all tasks are finished.
+ // 3. Every loop we have a second loop that pops an id from the ready_queue of the executor and
+ // polls the task (we guard against spurious wakeups or if there is no task that is tied
+ // with our id). We get the `Waker` and poll() the future. If `NotReady` we insert the task
+ // and its id back into the tasks queue. The Waker contains the id of the task that must be
+ // awaken and run. It is not the responsibility of the `Executor` to wake the `Waker`.
+ // 4. If there is more than one task in our executor we show some information and reastart the
+ // loop
+ // 5. Otherwise we just break and our async program is over.
+ pub fn block_on<F>(&mut self, future: F)
+ where
+ F: Future<Output = String> + 'static,
+ {
+ spawn(future);
+ loop {
+ while let Some(id) = self.pop_ready() {
+ let mut future = match self.get_future(id) {
+ Some(f) => f,
+ // guard against false wakeups
+ None => continue,
+ };
+ let waker = self.get_waker(id);
+ match future.poll(&waker) {
+ PollState::NotReady => self.insert_task(id, future),
+ PollState::Ready(_) => continue,
+ }
+ }
+ let task_count = self.task_count();
+ let name = String::from(thread::current().name().unwrap_or_default());
+
+ if task_count > 0 {
+ println!("{name}: {task_count}, pending tasks. Sleep until notified.");
+ thread::park();
+ } else {
+ println!("{name}: All tasks finished");
+ break;
+ }
+ }
+ }
+}
diff --git a/codes/reactor_executor/src/runtime/reactor.rs b/codes/reactor_executor/src/runtime/reactor.rs
new file mode 100644
index 0000000000000000000000000000000000000000..9e1a264a096c059c070e3cb399a51bae8b6b3945
--- /dev/null
+++ b/codes/reactor_executor/src/runtime/reactor.rs
@@ -0,0 +1,102 @@
+use std::{
+ collections::HashMap,
+ sync::{atomic::AtomicUsize, Arc, Mutex, OnceLock},
+};
+
+use mio::{net::TcpStream, Events, Interest, Poll, Registry, Token};
+
+use crate::runtime::Waker;
+
+type Wakers = Arc<Mutex<HashMap<usize, Waker>>>;
+
+// The REACTOR may be accessed from variuous threads and must therefore be hidden behind a lock.
+// Also it must never change one initialized when we start the reactor.
+static REACTOR: OnceLock<Reactor> = OnceLock::new();
+
+// To access the Reractor that will be borrowed from various places
+pub fn reactor() -> &'static Reactor {
+ REACTOR.get().expect("Called outside a runtime context")
+}
+
+// The reactor will be made of three fields:
+//
+// 1. A list of wakers that is a HashMap of id, Waker
+// 2. The registry that will help us interact with the Poll event queue
+// 3. The next available id for a Waker.
+pub struct Reactor {
+ wakers: Wakers,
+ registry: Registry,
+ next_id: AtomicUsize,
+}
+
+impl Reactor {
+ // We register interest for the `TcpStream` for a given interest and assign it the `id` in
+ // argumetn as a Token
+ pub fn register(&self, stream: &mut TcpStream, interest: Interest, id: usize) {
+ self.registry.register(stream, Token(id), interest).unwrap()
+ }
+
+ // Adds a waker into the `Wakers` `HashMap` along with its `id`. We replace the `Waker` if one
+ // with the same `id` is already present
+ pub fn set_waker(&self, waker: &Waker, id: usize) {
+ self.wakers
+ .lock()
+ .map(|mut w| w.insert(id, waker.clone()))
+ .unwrap();
+ }
+
+ // Removes a `Waker` from our `HashMap` and deregisters the `TcpStream` from the `Poll`
+ // instance
+ pub fn deregister(&self, stream: &mut TcpStream, id: usize) {
+ self.wakers.lock().map(|mut w| w.remove(&id)).unwrap();
+ self.registry.deregister(stream).unwrap();
+ }
+
+ // Increments the counter atomically. Relaxed just means atomicity. Other possiblities of
+ // Ordering can garantee that there is a certain ordering in how values are added from
+ // different threads.
+ pub fn next_id(&self) -> usize {
+ self.next_id
+ .fetch_add(1, std::sync::atomic::Ordering::Relaxed)
+ }
+}
+
+// 1. We poll events without a timeout in an infinite loop
+// 2. For each event we get the token associated to the events (it is the id that was passed upon
+// creation of the interest)
+// 3. We `wake()` the waker by id
+fn event_loop(mut poll: Poll, wakers: Wakers) {
+ let mut events = Events::with_capacity(100);
+ loop {
+ poll.poll(&mut events, None).unwrap();
+ events.iter().for_each(|e| {
+ let Token(id) = e.token();
+ let wakers = wakers.lock().unwrap();
+
+ if let Some(waker) = wakers.get(&id) {
+ waker.wake();
+ }
+ });
+ }
+}
+
+// This function starts the Reactor by:
+// 1. Creating the Wakers HashMap and the Poll instance.
+// 2. Cloning the registry used for the source (the TcpStream)
+// 3. Creating a new Reactor
+// 4. Initializing the static variable REACTOR and making sure no other instance is running
+// 5. Starting the `envent_loop()` for this Poll and Wakers and move it into a separate thread (we
+// never take ownership again of Poll)
+pub fn start() {
+ let wakers = Arc::new(Mutex::new(HashMap::<usize, Waker>::new()));
+ let poll = Poll::new().unwrap();
+ let registry = poll.registry().try_clone().unwrap();
+ let next_id = AtomicUsize::new(1);
+ let reactor = Reactor {
+ wakers: wakers.clone(),
+ registry,
+ next_id,
+ };
+ REACTOR.set(reactor).ok().expect("Rector already running");
+ std::thread::spawn(move || event_loop(poll, wakers));
+}