From 0984849288c2ba52347c16be8263a1c2d7ab8936 Mon Sep 17 00:00:00 2001
From: "Aode (Lion)" <asonix@asonix.dog>
Date: Tue, 22 Feb 2022 13:04:06 -0600
Subject: [PATCH] Noodles for every philosopher

---
 .gitignore  |   1 +
 Cargo.lock  |   7 ++++
 Cargo.toml  |   8 ++++
 src/main.rs | 116 ++++++++++++++++++++++++++++++++++++++++++++++++++++
 4 files changed, 132 insertions(+)
 create mode 100644 .gitignore
 create mode 100644 Cargo.lock
 create mode 100644 Cargo.toml
 create mode 100644 src/main.rs

diff --git a/.gitignore b/.gitignore
new file mode 100644
index 0000000..ea8c4bf
--- /dev/null
+++ b/.gitignore
@@ -0,0 +1 @@
+/target
diff --git a/Cargo.lock b/Cargo.lock
new file mode 100644
index 0000000..04da715
--- /dev/null
+++ b/Cargo.lock
@@ -0,0 +1,7 @@
+# This file is automatically @generated by Cargo.
+# It is not intended for manual editing.
+version = 3
+
+[[package]]
+name = "philosophy"
+version = "0.1.0"
diff --git a/Cargo.toml b/Cargo.toml
new file mode 100644
index 0000000..af2692a
--- /dev/null
+++ b/Cargo.toml
@@ -0,0 +1,8 @@
+[package]
+name = "philosophy"
+version = "0.1.0"
+edition = "2021"
+
+# See more keys and their definitions at https://doc.rust-lang.org/cargo/reference/manifest.html
+
+[dependencies]
diff --git a/src/main.rs b/src/main.rs
new file mode 100644
index 0000000..55cff5a
--- /dev/null
+++ b/src/main.rs
@@ -0,0 +1,116 @@
+use std::sync::{Arc, Mutex};
+
+async fn eat(philosopher: usize, ForkId(first): ForkId, ForkId(second): ForkId) {
+    for _ in 0..3 {
+        println!(
+            "Philosopher {}: I'm eating with forks {} and {}",
+            philosopher, first, second
+        );
+        yield_now().await;
+    }
+}
+
+fn philosopher(
+    id: usize,
+    first: Arc<Mutex<ForkId>>,
+    second: Arc<Mutex<ForkId>>,
+) -> std::pin::Pin<Box<dyn std::future::Future<Output = ()>>> {
+    Box::pin(async move {
+        loop {
+            if let Ok(first_guard) = first.try_lock() {
+                println!("Philosopher {}: got first guard", id);
+                yield_now().await;
+                if let Ok(second_guard) = second.try_lock() {
+                    eat(id, *first_guard, *second_guard).await;
+
+                    drop(second_guard);
+                    drop(first_guard);
+                    break;
+                }
+                println!("Philosopher {}: did not get second guard", id);
+                yield_now().await;
+                drop(first_guard);
+                continue;
+            }
+            println!("Philosopher {}: did not get first guard", id);
+            yield_now().await;
+        }
+    })
+}
+
+fn philosophy(num_philosophers: usize) {
+    let mut mutexes = Vec::new();
+    for i in 0..num_philosophers {
+        mutexes.push(Arc::new(Mutex::new(ForkId(i))));
+    }
+
+    let mut futures = Vec::new();
+    for i in 0..num_philosophers {
+        let next_index = (i + 1) % num_philosophers;
+
+        let [first_index, second_index] = if (i % 2) == 0 {
+            [i, next_index]
+        } else {
+            [next_index, i]
+        };
+
+        let first = Arc::clone(&mutexes[first_index]);
+        let second = Arc::clone(&mutexes[second_index]);
+
+        futures.push(philosopher(i, first, second));
+    }
+
+    let waker = Arc::new(DummyWaker).into();
+    let mut context = std::task::Context::from_waker(&waker);
+
+    for iteration in 0.. {
+        println!("state at {}:", iteration);
+        futures = futures.drain(..).filter_map(|mut future| {
+            if future.as_mut().poll(&mut context).is_ready() {
+                None
+            } else {
+                Some(future)
+            }
+        }).collect();
+
+        if futures.is_empty() {
+            break;
+        }
+    }
+
+    println!("Hello, world!");
+}
+
+fn main() {
+    philosophy(4096);
+}
+
+#[derive(Clone, Copy)]
+struct ForkId(usize);
+
+struct YieldNow(Option<()>);
+
+struct DummyWaker;
+impl std::task::Wake for DummyWaker {
+    fn wake(self: Arc<Self>) {}
+    fn wake_by_ref(self: &Arc<Self>) {}
+}
+
+impl std::future::Future for YieldNow {
+    type Output = ();
+
+    fn poll(
+        mut self: std::pin::Pin<&mut Self>,
+        _: &mut std::task::Context<'_>,
+    ) -> std::task::Poll<Self::Output> {
+        if let Some(()) = self.as_mut().0.take() {
+            std::task::Poll::Pending
+        } else {
+            std::task::Poll::Ready(())
+        }
+    }
+}
+
+async fn yield_now() {
+    YieldNow(Some(())).await
+}