1 files changed, 101 insertions, 0 deletions
diff --git a/library/std/src/sys_common/mutex.rs b/library/std/src/sys_common/mutex.rs
new file mode 100644
index 00000000000..e66d8994147
--- /dev/null
+++ b/library/std/src/sys_common/mutex.rs
@@ -0,0 +1,101 @@
+use crate::sys::mutex as imp;
+
+/// An OS-based mutual exclusion lock.
+///
+/// This is the thinnest cross-platform wrapper around OS mutexes. All usage of
+/// this mutex is unsafe and it is recommended to instead use the safe wrapper
+/// at the top level of the crate instead of this type.
+pub struct Mutex(imp::Mutex);
+
+unsafe impl Sync for Mutex {}
+
+impl Mutex {
+    /// Creates a new mutex for use.
+    ///
+    /// Behavior is undefined if the mutex is moved after it is
+    /// first used with any of the functions below.
+    /// Also, until `init` is called, behavior is undefined if this
+    /// mutex is ever used reentrantly, i.e., `raw_lock` or `try_lock`
+    /// are called by the thread currently holding the lock.
+    #[rustc_const_stable(feature = "const_sys_mutex_new", since = "1.0.0")]
+    pub const fn new() -> Mutex {
+        Mutex(imp::Mutex::new())
+    }
+
+    /// Prepare the mutex for use.
+    ///
+    /// This should be called once the mutex is at a stable memory address.
+    /// If called, this must be the very first thing that happens to the mutex.
+    /// Calling it in parallel with or after any operation (including another
+    /// `init()`) is undefined behavior.
+    #[inline]
+    pub unsafe fn init(&mut self) {
+        self.0.init()
+    }
+
+    /// Locks the mutex blocking the current thread until it is available.
+    ///
+    /// Behavior is undefined if the mutex has been moved between this and any
+    /// previous function call.
+    #[inline]
+    pub unsafe fn raw_lock(&self) {
+        self.0.lock()
+    }
+
+    /// Calls raw_lock() and then returns an RAII guard to guarantee the mutex
+    /// will be unlocked.
+    #[inline]
+    pub unsafe fn lock(&self) -> MutexGuard<'_> {
+        self.raw_lock();
+        MutexGuard(&self.0)
+    }
+
+    /// Attempts to lock the mutex without blocking, returning whether it was
+    /// successfully acquired or not.
+    ///
+    /// Behavior is undefined if the mutex has been moved between this and any
+    /// previous function call.
+    #[inline]
+    pub unsafe fn try_lock(&self) -> bool {
+        self.0.try_lock()
+    }
+
+    /// Unlocks the mutex.
+    ///
+    /// Behavior is undefined if the current thread does not actually hold the
+    /// mutex.
+    ///
+    /// Consider switching from the pair of raw_lock() and raw_unlock() to
+    /// lock() whenever possible.
+    #[inline]
+    pub unsafe fn raw_unlock(&self) {
+        self.0.unlock()
+    }
+
+    /// Deallocates all resources associated with this mutex.
+    ///
+    /// Behavior is undefined if there are current or will be future users of
+    /// this mutex.
+    #[inline]
+    pub unsafe fn destroy(&self) {
+        self.0.destroy()
+    }
+}
+
+// not meant to be exported to the outside world, just the containing module
+pub fn raw(mutex: &Mutex) -> &imp::Mutex {
+    &mutex.0
+}
+
+#[must_use]
+/// A simple RAII utility for the above Mutex without the poisoning semantics.
+pub struct MutexGuard<'a>(&'a imp::Mutex);
+
+impl Drop for MutexGuard<'_> {
+    #[inline]
+    fn drop(&mut self) {
+        unsafe {
+            self.0.unlock();
+        }
+    }
+}