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first draft of first chapter

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@@ -152,20 +152,22 @@
<main>
<h1><a class="header" href="#introduction" id="introduction">Introduction</a></h1>
<h1><a class="header" href="#some-background-information" id="some-background-information">Some background information</a></h1>
<p>Before we start implementing our <code>Futures</code>, we'll go through some background
<p>Before we start implementing our <code>Futures</code> , we'll go through some background
information that will help demystify some of the concepts we encounter.</p>
<h2><a class="header" href="#concurrency-in-general" id="concurrency-in-general">Concurrency in general</a></h2>
<p>If you find the concepts of concurrency and async programming confusing in
general, I know where you're coming from and I have written some resources to
try to give a high level overview that will make it easier to learn Rusts
<code>Futures</code> afterwards:</p>
<p><a href="https://cfsamson.github.io/book-exploring-async-basics/1_concurrent_vs_parallel.html">Async Basics - The difference between concurrency and parallelism</a>
<a href="https://cfsamson.github.io/book-exploring-async-basics/2_async_history.html">Async Basics - Async history</a>
<a href="https://cfsamson.github.io/book-exploring-async-basics/5_strategies_for_handling_io.html">Async Basics - Strategies for handling I/O</a>
<a href="https://cfsamson.github.io/book-exploring-async-basics/6_epoll_kqueue_iocp.html">Async Basics - Epoll, Kqueue and IOCP</a></p>
<ul>
<li><a href="https://cfsamson.github.io/book-exploring-async-basics/1_concurrent_vs_parallel.html">Async Basics - The difference between concurrency and parallelism</a></li>
<li><a href="https://cfsamson.github.io/book-exploring-async-basics/2_async_history.html">Async Basics - Async history</a></li>
<li><a href="https://cfsamson.github.io/book-exploring-async-basics/5_strategies_for_handling_io.html">Async Basics - Strategies for handling I/O</a></li>
<li><a href="https://cfsamson.github.io/book-exploring-async-basics/6_epoll_kqueue_iocp.html">Async Basics - Epoll, Kqueue and IOCP</a></li>
</ul>
<h2><a class="header" href="#trait-objects-and-dynamic-dispatch" id="trait-objects-and-dynamic-dispatch">Trait objects and dynamic dispatch</a></h2>
<p>The single most confusing topic we encounter when implementing our own <code>Futures</code>
is how we implement a <code>Waker</code>. Creating a <code>Waker</code> involves creating a <code>vtable</code>
<p>The single most confusing topic we encounter when implementing our own <code>Futures</code>
is how we implement a <code>Waker</code> . Creating a <code>Waker</code> involves creating a <code>vtable</code>
which allows using dynamic dispatch to call methods on a <em>type erased</em> trait
object we construct our selves.</p>
<p>If you want to know more about dynamic dispatch in Rust I can recommend this article:</p>
@@ -193,16 +195,14 @@ fn main() {
Most are 8 bytes (which is a pointer size on 64 bit systems), but some are 16
bytes.</p>
<p>The 16 byte sized pointers are called &quot;fat pointers&quot; since they carry more extra
information. </p>
<p><strong>In the case of <code>&amp;[i32]</code>:</strong> </p>
information.</p>
<p><strong>In the case of <code>&amp;[i32]</code> :</strong> </p>
<ul>
<li>
<p>The first 8 bytes is the actual pointer to the first element in the array
(or part of an array the slice refers to)</p>
</li>
<li>
<p>The second 8 bytes is the length of the slice.</p>
</li>
<li>The first 8 bytes is the actual pointer to the first element in the array</li>
</ul>
<p>(or part of an array the slice refers to)</p>
<ul>
<li>The second 8 bytes is the length of the slice.</li>
</ul>
<p>The one we'll concern ourselves about is the references to traits, or
<em>trait objects</em> as they're called in Rust.</p>
@@ -217,7 +217,7 @@ except that it implements the methods defined by our trait. To allow this we use
dynamic dispatch.</p>
<p>Let's explain this in code instead of words by implementing our own trait
object from these parts:</p>
<pre><pre class="playpen"><code class="language-rust editable">// A reference to a trait object is a fat pointer: (data_ptr, vtable_ptr)
<pre><pre class="playpen"><code class="language-rust">// A reference to a trait object is a fat pointer: (data_ptr, vtable_ptr)
trait Test {
fn add(&amp;self) -&gt; i32;
fn sub(&amp;self) -&gt; i32;
@@ -278,14 +278,319 @@ fn main() {
</code></pre></pre>
<p>If you run this code by pressing the &quot;play&quot; button at the top you'll se it
outputs just what we expect. </p>
outputs just what we expect.</p>
<p>This code example is editable so you can change it
and run it to see what happens.</p>
<p>The reason we go through this will be clear later on when we implement our own
<code>Waker</code> we'll actually set up a <code>vtable</code> like we do here to and knowing what
it is will make this much less mysterious.</p>
<h2><a class="header" href="#reactorexecutor-pattern" id="reactorexecutor-pattern">Reactor/Executor pattern</a></h2>
<p>If you don't know what this is, you should take a few minutes and read about
it. You will encounter the term <code>Reactor</code> and <code>Executor</code> a lot when working
with async code in Rust.</p>
<p>I have written a quick introduction explaining this pattern before which you
can take a look at here:</p>
<p><a href="https://cfsamsonbooks.gitbook.io/epoll-kqueue-iocp-explained/appendix-1/reactor-executor-pattern"><img src="./assets/reactorexecutor.png" alt="homepage" /></a></p>
<div style="text-align:center">
<a href="https://cfsamsonbooks.gitbook.io/epoll-kqueue-iocp-explained/appendix-1/reactor-executor-pattern">Epoll, Kqueue and IOCP Explained - The Reactor-Executor Pattern</a>
</div>
<p>I'll re-iterate the most important parts here.</p>
<p>This pattern consists of at least 2 parts:</p>
<ol>
<li>A reactor
<ul>
<li>handles some kind of event queue</li>
<li>has the responsibility of respoonding to events</li>
</ul>
</li>
<li>An executor
<ul>
<li>Often has a scheduler</li>
<li>Holds a set of suspended tasks, and has the responsibility of resuming
them when an event has occurred</li>
</ul>
</li>
<li>The concept of a task
<ul>
<li>A set of operations that can be stopped half way and resumed later on</li>
</ul>
</li>
</ol>
<p>This is a pattern not only used in Rust, but it's very popular in Rust due to
how well it separates concerns between handling and scheduling tasks, and queing
and responding to I/O events.</p>
<p>The only thing Rust as a language defines is the <em>task</em>. In Rust we call an
incorruptible task a <code>Future</code>. Futures has a well defined interface, which means
they can be used across the entire ecosystem.</p>
<p>In addition, Rust provides a way for the Reactor and Executor to communicate
through the <code>Waker</code>. We'll get to know these in the following chapters.</p>
<p>Providing these pieces let's Rust take care a lot of the ergonomic &quot;friction&quot;
programmers meet when faced with async code, and still not dictate any
preferred runtime to actually do the scheduling and I/O queues.</p>
<p>It's important to know that Rust doesn't provide a runtime, so you have to choose
one. <a href="https://github.com/async-rs/async-std">async std</a> and <a href="">tokio</a> are two popular ones.</p>
<p>With that out of the way, let's move on to our main example.</p>
<h1><a class="header" href="#naive-example" id="naive-example">Naive example</a></h1>
<pre><pre class="playpen"><code class="language-rust">use std::sync::atomic::{AtomicUsize, Ordering};
use std::sync::mpsc::{channel, Sender};
use std::sync::{Arc, Mutex};
use std::thread::{self, JoinHandle};
use std::time::{Duration, Instant};
fn main() {
let readylist = Arc::new(Mutex::new(vec![]));
let mut reactor = Reactor::new();
let mywaker = MyWaker::new(1, thread::current(), readylist.clone());
reactor.register(2, mywaker);
let mywaker = MyWaker::new(2, thread::current(), readylist.clone());
reactor.register(2, mywaker);
executor_run(reactor, readylist);
}
// ====== EXECUTOR ======
fn executor_run(mut reactor: Reactor, rl: Arc&lt;Mutex&lt;Vec&lt;usize&gt;&gt;&gt;) {
let start = Instant::now();
loop {
let mut rl_locked = rl.lock().unwrap();
while let Some(event) = rl_locked.pop() {
let dur = (Instant::now() - start).as_secs_f32();
println!(&quot;Event {} just happened at time: {:.2}.&quot;, event, dur);
reactor.outstanding.fetch_sub(1, Ordering::Relaxed);
}
drop(rl_locked);
if reactor.outstanding.load(Ordering::Relaxed) == 0 {
reactor.close();
break;
}
thread::park();
}
}
// ====== &quot;FUTURE&quot; IMPL ======
#[derive(Debug)]
struct MyWaker {
id: usize,
thread: thread::Thread,
readylist: Arc&lt;Mutex&lt;Vec&lt;usize&gt;&gt;&gt;,
}
impl MyWaker {
fn new(id: usize, thread: thread::Thread, readylist: Arc&lt;Mutex&lt;Vec&lt;usize&gt;&gt;&gt;) -&gt; Self {
MyWaker {
id,
thread,
readylist,
}
}
fn wake(&amp;self) {
self.readylist.lock().map(|mut rl| rl.push(self.id)).unwrap();
self.thread.unpark();
}
}
#[derive(Debug, Clone)]
pub struct Task {
id: usize,
pending: bool,
}
// ===== REACTOR =====
struct Reactor {
dispatcher: Sender&lt;Event&gt;,
handle: Option&lt;JoinHandle&lt;()&gt;&gt;,
outstanding: AtomicUsize,
}
#[derive(Debug)]
enum Event {
Close,
Simple(MyWaker, u64),
}
impl Reactor {
fn new() -&gt; Self {
let (tx, rx) = channel::&lt;Event&gt;();
let mut handles = vec![];
let handle = thread::spawn(move || {
// This simulates some I/O resource
for event in rx {
match event {
Event::Close =&gt; break,
Event::Simple(mywaker, duration) =&gt; {
let event_handle = thread::spawn(move || {
thread::sleep(Duration::from_secs(duration));
mywaker.wake();
});
handles.push(event_handle);
}
}
}
for handle in handles {
handle.join().unwrap();
}
});
Reactor {
dispatcher: tx,
handle: Some(handle),
outstanding: AtomicUsize::new(0),
}
}
fn register(&amp;mut self, duration: u64, mywaker: MyWaker) {
self.dispatcher
.send(Event::Simple(mywaker, duration))
.unwrap();
self.outstanding.fetch_add(1, Ordering::Relaxed);
}
fn close(&amp;mut self) {
self.dispatcher.send(Event::Close).unwrap();
}
}
impl Drop for Reactor {
fn drop(&amp;mut self) {
self.handle.take().map(|h| h.join().unwrap()).unwrap();
}
}
</code></pre></pre>
<pre><pre class="playpen"><code class="language-rust editable">use std::sync::atomic::{AtomicUsize, Ordering};
use std::sync::mpsc::{channel, Sender};
use std::sync::{Arc, Mutex};
use std::thread::{self, JoinHandle};
use std::time::{Duration, Instant};
fn main() {
let readylist = Arc::new(Mutex::new(vec![]));
let mut reactor = Reactor::new();
let mywaker = MyWaker::new(1, thread::current(), readylist.clone());
reactor.register(2, mywaker);
let mywaker = MyWaker::new(2, thread::current(), readylist.clone());
reactor.register(2, mywaker);
executor_run(reactor, readylist);
}
<span class="boring">// ====== EXECUTOR ======
</span><span class="boring">fn executor_run(mut reactor: Reactor, rl: Arc&lt;Mutex&lt;Vec&lt;usize&gt;&gt;&gt;) {
</span><span class="boring"> let start = Instant::now();
</span><span class="boring"> loop {
</span><span class="boring"> let mut rl_locked = rl.lock().unwrap();
</span><span class="boring"> while let Some(event) = rl_locked.pop() {
</span><span class="boring"> let dur = (Instant::now() - start).as_secs_f32();
</span><span class="boring"> println!(&quot;Event {} just happened at time: {:.2}.&quot;, event, dur);
</span><span class="boring"> reactor.outstanding.fetch_sub(1, Ordering::Relaxed);
</span><span class="boring"> }
</span><span class="boring"> drop(rl_locked);
</span><span class="boring">
</span><span class="boring"> if reactor.outstanding.load(Ordering::Relaxed) == 0 {
</span><span class="boring"> reactor.close();
</span><span class="boring"> break;
</span><span class="boring"> }
</span><span class="boring">
</span><span class="boring"> thread::park();
</span><span class="boring"> }
</span><span class="boring">}
</span><span class="boring">
</span><span class="boring">// ====== &quot;FUTURE&quot; IMPL ======
</span><span class="boring">#[derive(Debug)]
</span><span class="boring">struct MyWaker {
</span><span class="boring"> id: usize,
</span><span class="boring"> thread: thread::Thread,
</span><span class="boring"> readylist: Arc&lt;Mutex&lt;Vec&lt;usize&gt;&gt;&gt;,
</span><span class="boring">}
</span><span class="boring">
</span><span class="boring">impl MyWaker {
</span><span class="boring"> fn new(id: usize, thread: thread::Thread, readylist: Arc&lt;Mutex&lt;Vec&lt;usize&gt;&gt;&gt;) -&gt; Self {
</span><span class="boring"> MyWaker {
</span><span class="boring"> id,
</span><span class="boring"> thread,
</span><span class="boring"> readylist,
</span><span class="boring"> }
</span><span class="boring"> }
</span><span class="boring">
</span><span class="boring"> fn wake(&amp;self) {
</span><span class="boring"> self.readylist.lock().map(|mut rl| rl.push(self.id)).unwrap();
</span><span class="boring"> self.thread.unpark();
</span><span class="boring"> }
</span><span class="boring">}
</span><span class="boring">
</span><span class="boring">
</span><span class="boring">#[derive(Debug, Clone)]
</span><span class="boring">pub struct Task {
</span><span class="boring"> id: usize,
</span><span class="boring"> pending: bool,
</span><span class="boring">}
</span><span class="boring">
</span><span class="boring">// ===== REACTOR =====
</span><span class="boring">struct Reactor {
</span><span class="boring"> dispatcher: Sender&lt;Event&gt;,
</span><span class="boring"> handle: Option&lt;JoinHandle&lt;()&gt;&gt;,
</span><span class="boring"> outstanding: AtomicUsize,
</span><span class="boring">}
</span><span class="boring">#[derive(Debug)]
</span><span class="boring">enum Event {
</span><span class="boring"> Close,
</span><span class="boring"> Simple(MyWaker, u64),
</span><span class="boring">}
</span><span class="boring">
</span><span class="boring">impl Reactor {
</span><span class="boring"> fn new() -&gt; Self {
</span><span class="boring"> let (tx, rx) = channel::&lt;Event&gt;();
</span><span class="boring"> let mut handles = vec![];
</span><span class="boring"> let handle = thread::spawn(move || {
</span><span class="boring"> // This simulates some I/O resource
</span><span class="boring"> for event in rx {
</span><span class="boring"> match event {
</span><span class="boring"> Event::Close =&gt; break,
</span><span class="boring"> Event::Simple(mywaker, duration) =&gt; {
</span><span class="boring"> let event_handle = thread::spawn(move || {
</span><span class="boring"> thread::sleep(Duration::from_secs(duration));
</span><span class="boring"> mywaker.wake();
</span><span class="boring"> });
</span><span class="boring"> handles.push(event_handle);
</span><span class="boring"> }
</span><span class="boring"> }
</span><span class="boring"> }
</span><span class="boring">
</span><span class="boring"> for handle in handles {
</span><span class="boring"> handle.join().unwrap();
</span><span class="boring"> }
</span><span class="boring"> });
</span><span class="boring">
</span><span class="boring"> Reactor {
</span><span class="boring"> dispatcher: tx,
</span><span class="boring"> handle: Some(handle),
</span><span class="boring"> outstanding: AtomicUsize::new(0),
</span><span class="boring"> }
</span><span class="boring"> }
</span><span class="boring">
</span><span class="boring"> fn register(&amp;mut self, duration: u64, mywaker: MyWaker) {
</span><span class="boring"> self.dispatcher
</span><span class="boring"> .send(Event::Simple(mywaker, duration))
</span><span class="boring"> .unwrap();
</span><span class="boring"> self.outstanding.fetch_add(1, Ordering::Relaxed);
</span><span class="boring"> }
</span><span class="boring">
</span><span class="boring"> fn close(&amp;mut self) {
</span><span class="boring"> self.dispatcher.send(Event::Close).unwrap();
</span><span class="boring"> }
</span><span class="boring">}
</span><span class="boring">
</span><span class="boring">impl Drop for Reactor {
</span><span class="boring"> fn drop(&amp;mut self) {
</span><span class="boring"> self.handle.take().map(|h| h.join().unwrap()).unwrap();
</span><span class="boring"> }
</span><span class="boring">}
</span></code></pre></pre>
<h1><a class="header" href="#proper-waker" id="proper-waker">Proper Waker</a></h1>
<h1><a class="header" href="#proper-future" id="proper-future">Proper Future</a></h1>
<h1><a class="header" href="#supporting-asyncawait" id="supporting-asyncawait">Supporting async/await</a></h1>
@@ -313,6 +618,21 @@ it is will make this much less mysterious.</p>
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