Permalink
Browse files

Auto merge of #41624 - RalfJung:mutexguard-sync, r=alexcrichton

MutexGuard<T> may be Sync only if T is Sync

Fixes #41622

This is a breaking change. Does that imply any further process?

I am not sure whether I wrote that "compilation must fail"-test correctly, but at least it is passing here with the patch applied. Same for the `since = "1.18.0"`, I just picked it because I had to pick something.
  • Loading branch information...
bors committed May 3, 2017
2 parents 4d81b14 + 23522f6 commit 0634f0a30f94116ee13c16fb1a35c4c92253ab13
Showing with 25 additions and 5 deletions.
  1. +3 −5 src/libstd/sync/mutex.rs
  2. +22 −0 src/test/compile-fail/mutexguard-sync.rs
@@ -10,7 +10,6 @@
use cell::UnsafeCell;
use fmt;
use marker;
use mem;
use ops::{Deref, DerefMut};
use ptr;
@@ -153,7 +152,9 @@ pub struct MutexGuard<'a, T: ?Sized + 'a> {
}
#[stable(feature = "rust1", since = "1.0.0")]
impl<'a, T: ?Sized> !marker::Send for MutexGuard<'a, T> {}
impl<'a, T: ?Sized> !Send for MutexGuard<'a, T> { }
#[stable(feature = "mutexguard", since = "1.18.0")]
unsafe impl<'a, T: ?Sized + Sync> Sync for MutexGuard<'a, T> { }
impl<T> Mutex<T> {
/// Creates a new mutex in an unlocked state ready for use.
@@ -459,9 +460,6 @@ mod tests {
#[derive(Eq, PartialEq, Debug)]
struct NonCopy(i32);
unsafe impl<T: Send> Send for Packet<T> {}
unsafe impl<T> Sync for Packet<T> {}
#[test]
fn smoke() {
let m = Mutex::new(());
@@ -0,0 +1,22 @@
// Copyright 2017 The Rust Project Developers. See the COPYRIGHT
// file at the top-level directory of this distribution and at
// http://rust-lang.org/COPYRIGHT.
//
// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
// option. This file may not be copied, modified, or distributed
// except according to those terms.
// MutexGuard<Cell<i32>> must not be Sync, that would be unsound.
use std::sync::Mutex;
use std::cell::Cell;
fn test_sync<T: Sync>(_t: T) {}
fn main()
{
let m = Mutex::new(Cell::new(0i32));
let guard = m.lock().unwrap();
test_sync(guard); //~ ERROR the trait bound
}

0 comments on commit 0634f0a

Please sign in to comment.