From 425432ba6c91e6aa92e459528507120ecd613e6e Mon Sep 17 00:00:00 2001
From: Ralf Jung <post@ralfj.de>
Date: Wed, 28 Aug 2019 23:41:04 +0200
Subject: [PATCH] use raw ptr for racy load and add comment (#289)

---
 src/bytes.rs | 7 +++++--
 1 file changed, 5 insertions(+), 2 deletions(-)

diff --git a/src/bytes.rs b/src/bytes.rs
index b9626490c..6282cf4fb 100644
--- a/src/bytes.rs
+++ b/src/bytes.rs
@@ -1940,8 +1940,11 @@ impl Inner {
 
     #[inline]
     fn inline_len(&self) -> usize {
-        let p: &usize = unsafe { mem::transmute(&self.arc) };
-        (p & INLINE_LEN_MASK) >> INLINE_LEN_OFFSET
+        // This is undefind behavior due to a data race, but experimental
+        // evidence shows that it works in practice (discussion:
+        // https://internals.rust-lang.org/t/bit-wise-reasoning-for-atomic-accesses/8853).
+        let p: *const usize = unsafe { mem::transmute(&self.arc) };
+        (unsafe { *p } & INLINE_LEN_MASK) >> INLINE_LEN_OFFSET
     }
 
     /// Set the length of the inline buffer. This is done by writing to the