1 files changed, 88 insertions, 0 deletions
diff --git a/library/std/src/sys_common/rwlock.rs b/library/std/src/sys_common/rwlock.rs
new file mode 100644
index 00000000000..3705d641a1b
--- /dev/null
+++ b/library/std/src/sys_common/rwlock.rs
@@ -0,0 +1,88 @@
+use crate::sys::rwlock as imp;
+
+/// An OS-based reader-writer lock.
+///
+/// This structure is entirely unsafe and serves as the lowest layer of a
+/// cross-platform binding of system rwlocks. It is recommended to use the
+/// safer types at the top level of this crate instead of this type.
+pub struct RWLock(imp::RWLock);
+
+impl RWLock {
+    /// Creates a new reader-writer lock for use.
+    ///
+    /// Behavior is undefined if the reader-writer lock is moved after it is
+    /// first used with any of the functions below.
+    pub const fn new() -> RWLock {
+        RWLock(imp::RWLock::new())
+    }
+
+    /// Acquires shared access to the underlying lock, blocking the current
+    /// thread to do so.
+    ///
+    /// Behavior is undefined if the rwlock has been moved between this and any
+    /// previous method call.
+    #[inline]
+    pub unsafe fn read(&self) {
+        self.0.read()
+    }
+
+    /// Attempts to acquire shared access to this lock, returning whether it
+    /// succeeded or not.
+    ///
+    /// This function does not block the current thread.
+    ///
+    /// Behavior is undefined if the rwlock has been moved between this and any
+    /// previous method call.
+    #[inline]
+    pub unsafe fn try_read(&self) -> bool {
+        self.0.try_read()
+    }
+
+    /// Acquires write access to the underlying lock, blocking the current thread
+    /// to do so.
+    ///
+    /// Behavior is undefined if the rwlock has been moved between this and any
+    /// previous method call.
+    #[inline]
+    pub unsafe fn write(&self) {
+        self.0.write()
+    }
+
+    /// Attempts to acquire exclusive access to this lock, returning whether it
+    /// succeeded or not.
+    ///
+    /// This function does not block the current thread.
+    ///
+    /// Behavior is undefined if the rwlock has been moved between this and any
+    /// previous method call.
+    #[inline]
+    pub unsafe fn try_write(&self) -> bool {
+        self.0.try_write()
+    }
+
+    /// Unlocks previously acquired shared access to this lock.
+    ///
+    /// Behavior is undefined if the current thread does not have shared access.
+    #[inline]
+    pub unsafe fn read_unlock(&self) {
+        self.0.read_unlock()
+    }
+
+    /// Unlocks previously acquired exclusive access to this lock.
+    ///
+    /// Behavior is undefined if the current thread does not currently have
+    /// exclusive access.
+    #[inline]
+    pub unsafe fn write_unlock(&self) {
+        self.0.write_unlock()
+    }
+
+    /// Destroys OS-related resources with this RWLock.
+    ///
+    /// Behavior is undefined if there are any currently active users of this
+    /// lock.
+    #[inline]
+    pub unsafe fn destroy(&self) {
+        self.0.destroy()
+    }
+}