From 0b49b056981f4c5bcbdbb7fada1a8379e0793c86 Mon Sep 17 00:00:00 2001
From: Botahamec <botahamec@outlook.com>
Date: Fri, 28 Oct 2022 22:20:05 -0400
Subject: Implemented SpinLock

---
 src/lib.rs   |  7 +++++--
 src/lock.rs  |  7 ++++++-
 src/mutex.rs | 33 +++++++++++++++++++++++++++++++++
 3 files changed, 44 insertions(+), 3 deletions(-)

(limited to 'src')

diff --git a/src/lib.rs b/src/lib.rs
index 615086d..2358ba2 100644
--- a/src/lib.rs
+++ b/src/lib.rs
@@ -1,6 +1,7 @@
 #![warn(clippy::pedantic)]
 #![warn(clippy::nursery)]
 #![allow(clippy::module_name_repetitions)]
+#![allow(clippy::declare_interior_mutable_const)]
 
 use std::any::type_name;
 use std::fmt::{self, Debug};
@@ -10,11 +11,13 @@ use once_cell::sync::Lazy;
 use thread_local::ThreadLocal;
 
 mod lock;
-pub mod mutex;
+mod mutex;
 
 use lock::{Key, Lock};
+use mutex::RawSpin;
 
-pub use mutex::Mutex;
+pub use mutex::{Mutex, MutexGuard};
+pub type SpinLock<T> = Mutex<RawSpin, T>;
 
 static KEY: Lazy<ThreadLocal<Lock>> = Lazy::new(ThreadLocal::new);
 
diff --git a/src/lock.rs b/src/lock.rs
index c69ce21..101a061 100644
--- a/src/lock.rs
+++ b/src/lock.rs
@@ -38,6 +38,11 @@ impl Lock {
 		}
 	}
 
+	/// Checks whether this `Lock` is currently locked.
+	pub fn is_locked(&self) -> bool {
+		self.is_locked.load(Ordering::Relaxed)
+	}
+
 	/// Attempt to lock the `Lock`.
 	///
 	/// If the lock is already locked, then this'll return false. If it is
@@ -56,7 +61,7 @@ impl Lock {
 	///
 	/// This should only be called if the key to the lock has been "lost". That
 	/// means the program no longer has a reference to the key.
-	unsafe fn force_unlock(&self) {
+	pub unsafe fn force_unlock(&self) {
 		self.is_locked.store(false, Ordering::Release);
 	}
 
diff --git a/src/mutex.rs b/src/mutex.rs
index a152eda..6c2e254 100644
--- a/src/mutex.rs
+++ b/src/mutex.rs
@@ -1,6 +1,7 @@
 use std::cell::UnsafeCell;
 use std::ops::{Deref, DerefMut};
 
+use crate::lock::Lock;
 use crate::ThreadKey;
 
 /// Implements a raw C-like mutex.
@@ -31,6 +32,38 @@ pub unsafe trait RawMutex {
 	unsafe fn unlock(&self);
 }
 
+/// A raw mutex which just spins
+pub struct RawSpin {
+	lock: Lock,
+}
+
+unsafe impl RawMutex for RawSpin {
+	const INIT: Self = Self { lock: Lock::new() };
+
+	fn lock(&self) {
+		loop {
+			std::hint::spin_loop();
+
+			if let Some(key) = self.lock.try_lock() {
+				std::mem::forget(key);
+				return;
+			}
+		}
+	}
+
+	fn try_lock(&self) -> bool {
+		self.lock.try_lock().is_some()
+	}
+
+	fn is_locked(&self) -> bool {
+		self.lock.is_locked()
+	}
+
+	unsafe fn unlock(&self) {
+		self.lock.force_unlock();
+	}
+}
+
 /// A mutual exclusion primitive useful for protecting shared data, which
 /// cannot deadlock.
 ///
-- 
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