1 files changed, 122 insertions, 0 deletions
diff --git a/src/no_threads.rs b/src/no_threads.rs
new file mode 100755
index 0000000..f831f5f
--- /dev/null
+++ b/src/no_threads.rs
@@ -0,0 +1,122 @@
+use core::cell::Cell;
+
+pub struct Mutex {
+	// This platform has no threads, so we can use a Cell here.
+	locked: Cell<bool>,
+}
+
+unsafe impl Send for Mutex {}
+unsafe impl Sync for Mutex {} // no threads on this platform
+
+impl Mutex {
+	#[inline]
+	pub const fn new() -> Mutex {
+		Mutex {
+			locked: Cell::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) {
+		if self.locked.replace(true) {
+			if cfg!(feature = "unsafe_lock") {
+				// safety: it's UB to lock this when it's already locked
+				unsafe { core::hint::unreachable_unchecked() };
+			} else {
+				panic!("deadlock on a platform with no threads");
+			}
+		}
+	}
+
+	/// 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 {
+		self.locked.replace(true) == false
+	}
+
+	/// 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.locked.get()
+	}
+}
+
+pub struct RwLock {
+	// This platform has no threads, so we can use a Cell here.
+	mode: Cell<isize>,
+}
+
+unsafe impl Send for RwLock {}
+unsafe impl Sync for RwLock {} // no threads on this platform
+
+impl RwLock {
+	#[inline]
+	pub const fn new() -> RwLock {
+		RwLock { mode: Cell::new(0) }
+	}
+
+	#[inline]
+	pub unsafe fn read(&self) {
+		let m = self.mode.get();
+		if m >= 0 {
+			self.mode.set(m + 1);
+		} else {
+			unsafe { core::hint::unreachable_unchecked() };
+		}
+	}
+
+	#[inline]
+	pub unsafe fn try_read(&self) -> bool {
+		let m = self.mode.get();
+		if m >= 0 {
+			self.mode.set(m + 1);
+			true
+		} else {
+			false
+		}
+	}
+
+	#[inline]
+	pub unsafe fn write(&self) {
+		if self.mode.replace(isize::MAX) != 0 {
+			unsafe { core::hint::unreachable_unchecked() };
+		}
+	}
+
+	#[inline]
+	pub unsafe fn try_write(&self) -> bool {
+		if self.mode.get() == 0 {
+			self.mode.set(-1);
+			true
+		} else {
+			false
+		}
+	}
+
+	#[inline]
+	pub unsafe fn read_unlock(&self) {
+		self.mode.set(self.mode.get() - 1);
+	}
+
+	#[inline]
+	pub unsafe fn write_unlock(&self) {
+		assert_eq!(self.mode.replace(0), -1);
+	}
+}