From dca4a79fffee4ec8e5c1ecd7849b0a378c481308 Mon Sep 17 00:00:00 2001
From: GuillaumeDIDIER <guillaume.didier95@hotmail.fr>
Date: Mon, 5 Oct 2020 15:25:46 +0200
Subject: [PATCH] Add turn lock

---
 Cargo.toml              |  3 +-
 turn_lock/.cargo/config |  2 ++
 turn_lock/Cargo.toml    |  9 ++++++
 turn_lock/src/lib.rs    | 68 +++++++++++++++++++++++++++++++++++++++++
 4 files changed, 81 insertions(+), 1 deletion(-)
 create mode 100644 turn_lock/.cargo/config
 create mode 100644 turn_lock/Cargo.toml
 create mode 100644 turn_lock/src/lib.rs

diff --git a/Cargo.toml b/Cargo.toml
index d619237..179c8ed 100644
--- a/Cargo.toml
+++ b/Cargo.toml
@@ -5,7 +5,8 @@ members = [
     "polling_serial",
     "cache_utils",
     "cpuid",
-    "aes-t-tables"
+    "aes-t-tables",
+    "turn_lock",
 ]
 
 [package]
diff --git a/turn_lock/.cargo/config b/turn_lock/.cargo/config
new file mode 100644
index 0000000..2f05654
--- /dev/null
+++ b/turn_lock/.cargo/config
@@ -0,0 +1,2 @@
+[build]
+target = "x86_64-unknown-linux-gnu"
diff --git a/turn_lock/Cargo.toml b/turn_lock/Cargo.toml
new file mode 100644
index 0000000..c9a1db3
--- /dev/null
+++ b/turn_lock/Cargo.toml
@@ -0,0 +1,9 @@
+[package]
+name = "turn_lock"
+version = "0.1.0"
+authors = ["GuillaumeDIDIER <guillaume.didier95@hotmail.fr>"]
+edition = "2018"
+
+# See more keys and their definitions at https://doc.rust-lang.org/cargo/reference/manifest.html
+
+[dependencies]
diff --git a/turn_lock/src/lib.rs b/turn_lock/src/lib.rs
new file mode 100644
index 0000000..124ad81
--- /dev/null
+++ b/turn_lock/src/lib.rs
@@ -0,0 +1,68 @@
+use std::sync::atomic::{spin_loop_hint, AtomicUsize, Ordering};
+use std::sync::Arc;
+
+pub struct TurnLock {
+    turn: Arc<AtomicUsize>,
+    index: usize,
+    num_turns: usize,
+}
+
+impl TurnLock {
+    pub fn new(num_turns: usize) -> Vec<Self> {
+        let turn = Arc::new(AtomicUsize::new(0));
+        let mut r = Vec::new();
+        for i in 0..num_turns {
+            r.push(TurnLock {
+                turn: turn.clone(),
+                index: i,
+                num_turns,
+            })
+        }
+        r
+    }
+    pub fn wait(&mut self) {
+        while self.turn.load(Ordering::Acquire) != self.index {
+            spin_loop_hint();
+        }
+        assert_eq!(self.turn.load(Ordering::Relaxed), self.index);
+    }
+    pub fn next(&mut self) {
+        assert_eq!(self.turn.load(Ordering::Relaxed), self.index);
+        let r = self.turn.compare_and_swap(
+            self.index,
+            (self.index + 1) % self.num_turns,
+            Ordering::Release,
+        );
+        if r != self.index {
+            panic!("Released lock out of turn");
+        }
+    }
+
+    pub fn current(&self) -> usize {
+        self.turn.load(Ordering::SeqCst)
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use crate::TurnLock;
+
+    #[test]
+    fn it_works() {
+        assert_eq!(2 + 2, 4);
+    }
+
+    #[test]
+    fn three_turns() {
+        let mut v = TurnLock::new(3);
+        v[0].wait();
+        v[0].next();
+        v[1].wait();
+        v[1].next();
+        v[2].wait();
+        v[2].next();
+        v[0].wait();
+        v[0].next();
+        assert_eq!(v[2].current(), 1);
+    }
+}