From 5a012c87d7aa676a85fcd5d86e1f157439a528bd Mon Sep 17 00:00:00 2001
From: nrath-js <nrath@janestreet.com>
Date: Sun, 8 Dec 2024 00:20:26 +0000
Subject: [PATCH] Mark libc's ``fs::Dir` as `Sync` (#1232)

This is safe since all methods that mutate the internal state require
a &mut self. It also makes behavior consistent with the linux_raw
backend (whose `fs::Dir` is Sync+Send).

Fixes: #1230.
---
 src/backend/libc/fs/dir.rs | 9 +++++----
 1 file changed, 5 insertions(+), 4 deletions(-)

diff --git a/src/backend/libc/fs/dir.rs b/src/backend/libc/fs/dir.rs
index 4b4676872..9865e13bb 100644
--- a/src/backend/libc/fs/dir.rs
+++ b/src/backend/libc/fs/dir.rs
@@ -227,11 +227,12 @@ impl Dir {
     }
 }
 
-/// `Dir` implements `Send` but not `Sync`, because we use `readdir` which is
-/// not guaranteed to be thread-safe. Users can wrap this in a `Mutex` if they
-/// need `Sync`, which is effectively what'd need to do to implement `Sync`
-/// ourselves.
+/// `Dir` is `Send` and `Sync`, because even though it contains internal
+/// state, all methods that modify the state require a `mut &self` and
+/// can therefore not be called concurrently. Calling them from different
+/// threads sequentially is fine.
 unsafe impl Send for Dir {}
+unsafe impl Sync for Dir {}
 
 impl Drop for Dir {
     #[inline]