From 1121a8eb23f6f0edd9f41cdc08331d40e18105ee Mon Sep 17 00:00:00 2001 From: Eliza Weisman Date: Fri, 3 Apr 2020 15:45:29 -0700 Subject: sync: ensure Mutex, RwLock, and Semaphore futures are Send + Sync (#2375) Previously, the `Mutex::lock`, `RwLock::{read, write}`, and `Semaphore::acquire` futures in `tokio::sync` implemented `Send + Sync` automatically. This was by virtue of being implemented using a `poll_fn` that only closed over `Send + Sync` types. However, this broke in PR #2325, which rewrote those types using the new `batch_semaphore`. Now, they await an `Acquire` future, which contains a `Waiter`, which internally contains an `UnsafeCell`, and thus does not implement `Sync`. Since removing previously implemented traits breaks existing code, this inadvertantly caused a breaking change. There were tests ensuring that the `Mutex`, `RwLock`, and `Semaphore` types themselves were `Send + Sync`, but no tests that the _futures they return_ implemented those traits. I've fixed this by adding an explicit impl of `Sync` for the `batch_semaphore::Acquire` future. Since the `Waiter` type held by this struct is only accessed when borrowed mutably, it is safe for it to implement `Sync`. Additionally, I've added to the bounds checks for the effected `tokio::sync` types to ensure that returned futures continue to implement `Send + Sync` in the future. --- tokio/CHANGELOG.md | 8 ++++++++ 1 file changed, 8 insertions(+) (limited to 'tokio/CHANGELOG.md') diff --git a/tokio/CHANGELOG.md b/tokio/CHANGELOG.md index b748408e..68e2af65 100644 --- a/tokio/CHANGELOG.md +++ b/tokio/CHANGELOG.md @@ -1,3 +1,11 @@ +# 0.2.16 (April 3, 2020) + +### Fixes + +- sync: fix a regression where `Mutex`, `Semaphore`, and `RwLock` futures no + longer implement `Sync` (#2375) + + # 0.2.15 (April 2, 2020) ### Fixes -- cgit v1.2.3