First commitHEADmain

1 files changed, 68 insertions, 0 deletions

diff --git a/src/spin.rs b/src/spin.rs
new file mode 100755
index 0000000..c81a1e7
--- /dev/null
+++ b/src/spin.rs
@@ -0,0 +1,68 @@
+use core::sync::atomic::{AtomicBool, Ordering};
+
+pub struct Mutex(AtomicBool);
+
+unsafe impl Send for Mutex {}
+unsafe impl Sync for Mutex {}
+
+impl Mutex {
+	#[inline]
+	pub const fn new() -> Mutex {
+		Mutex(AtomicBool::new(false))
+	}
+
+	/// Locks the mutex
+	///
+	/// # Safety
+	///
+	/// UB occurs if the mutex is already locked by the current thread and the
+	/// `unsafe_lock` feature is enabled.
+	#[inline]
+	pub unsafe fn lock(&self) {
+		// Can fail to lock even if the spinlock is not locked. May be more
+		// efficient than `try_lock` hen called in a loop.
+		loop {
+			if self.try_lock_weak() {
+				break;
+			}
+
+			while self.is_locked() {
+				core::hint::spin_loop();
+			}
+		}
+	}
+
+	/// If the mutex is unlocked, it is locked, and this function returns
+	/// `true'. Otherwise, `false` is returned.
+	#[inline]
+	pub unsafe fn try_lock(&self) -> bool {
+		// The reason for using a strong compare_exchange is explained here:
+		// https://github.com/Amanieu/parking_lot/pull/207#issuecomment-575869107
+		self.lock
+			.compare_exchange(false, true, Ordering::Acquire, Ordering::Relaxed)
+			.is_ok()
+	}
+
+	/// Unlocks the mutex
+	///
+	/// # Safety
+	///
+	/// UB occurs if the mutex is already unlocked or if it has been locked on
+	/// a different thread.
+	#[inline]
+	pub unsafe fn unlock(&self) {
+		self.locked.set(false);
+	}
+
+	#[inline]
+	pub unsafe fn is_locked(&self) -> bool {
+		self.lock.load(Ordering::Relaxed)
+	}
+
+	#[inline]
+	fn try_lock_weak(&self) -> bool {
+		self.lock
+			.compare_exchange_weak(false, true, Ordering::Acquire, Ordering::Relaxed)
+			.is_ok()
+	}
+}