Add more docs to new data_ptr methods

Author: jplatte

library/std/src/sync/poison/mutex.rs

@@ -610,6 +610,11 @@ impl<T: ?Sized> Mutex<T> {
     }
 
     /// Returns a raw pointer to the underlying data.
+    ///
+    /// The returned pointer is always non-null and properly aligned, but it is
+    /// the user's responsibility to ensure that any reads and writes through it
+    /// are properly synchronized to avoid data races, and that it is not read
+    /// or written through after the mutex is dropped.
     #[unstable(feature = "mutex_data_ptr", issue = "140368")]
     pub fn data_ptr(&self) -> *mut T {
         self.data.get()

library/std/src/sync/poison/rwlock.rs

@@ -636,6 +636,11 @@ impl<T: ?Sized> RwLock<T> {
     }
 
     /// Returns a raw pointer to the underlying data.
+    ///
+    /// The returned pointer is always non-null and properly aligned, but it is
+    /// the user's responsibility to ensure that any reads and writes through it
+    /// are properly synchronized to avoid data races, and that it is not read
+    /// or written through after the lock is dropped.
     #[unstable(feature = "rwlock_data_ptr", issue = "140368")]
     pub fn data_ptr(&self) -> *mut T {
         self.data.get()