From 73c66412b3c26bdc08b2f8886a20f5e13847fecf Mon Sep 17 00:00:00 2001
From: Taiki Endo <te316e89@gmail.com>
Date: Fri, 30 Aug 2019 19:10:37 +0900
Subject: [PATCH] Add Mutex::{get_mut, into_inner}

---
 futures-util/src/lock/mutex.rs | 38 +++++++++++++++++++++++++++++++++-
 1 file changed, 37 insertions(+), 1 deletion(-)

diff --git a/futures-util/src/lock/mutex.rs b/futures-util/src/lock/mutex.rs
index 832e75aff1..7e679782e9 100644
--- a/futures-util/src/lock/mutex.rs
+++ b/futures-util/src/lock/mutex.rs
@@ -67,10 +67,24 @@ impl<T> Mutex<T> {
     pub fn new(t: T) -> Mutex<T> {
         Mutex {
             state: AtomicUsize::new(0),
-            value: UnsafeCell::new(t),
             waiters: StdMutex::new(Slab::new()),
+            value: UnsafeCell::new(t),
         }
     }
+
+    /// Consumes this mutex, returning the underlying data.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use futures::lock::Mutex;
+    ///
+    /// let mutex = Mutex::new(0);
+    /// assert_eq!(mutex.into_inner(), 0);
+    /// ```
+    pub fn into_inner(self) -> T {
+        self.value.into_inner()
+    }
 }
 
 impl<T: ?Sized> Mutex<T> {
@@ -97,6 +111,28 @@ impl<T: ?Sized> Mutex<T> {
         }
     }
 
+    /// Returns a mutable reference to the underlying data.
+    ///
+    /// Since this call borrows the `Mutex` mutably, no actual locking needs to
+    /// take place -- the mutable borrow statically guarantees no locks exist.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// # futures::executor::block_on(async {
+    /// use futures::lock::Mutex;
+    ///
+    /// let mut mutex = Mutex::new(0);
+    /// *mutex.get_mut() = 10;
+    /// assert_eq!(*mutex.lock().await, 10);
+    /// # });
+    /// ```
+    pub fn get_mut(&mut self) -> &mut T {
+        // We know statically that there are no other references to `self`, so
+        // there's no need to lock the inner mutex.
+        unsafe { &mut *self.value.get() }
+    }
+
     fn remove_waker(&self, wait_key: usize, wake_another: bool) {
         if wait_key != WAIT_KEY_NONE {
             let mut waiters = self.waiters.lock().unwrap();