Auto merge of #51529 - nodakai:improve-sys_common-mutex, r=oli-obk

libstd: add an RAII utility for sys_common::mutex::Mutex

It is indeed debatable whether or not we should introduce more sophistication like this to the lowest layer of a system library. In fact, `Drop::drop()` cannot be `unsafe` (IIRC there was a discussion on introducing an unsafe variant of `Drop` whose entire scope must be within `unsafe`)

1 files changed, 1 insertions, 2 deletions

diff --git a/src/libstd/sys_common/thread_local.rs b/src/libstd/sys_common/thread_local.rs
index d0d6224de0a..75f6b9ac7fd 100644
--- a/src/libstd/sys_common/thread_local.rs
+++ b/src/libstd/sys_common/thread_local.rs
@@ -162,13 +162,12 @@ impl StaticKey {
         // we just simplify the whole branch.
         if imp::requires_synchronized_create() {
             static INIT_LOCK: Mutex = Mutex::new();
-            INIT_LOCK.lock();
+            let _guard = INIT_LOCK.lock();
             let mut key = self.key.load(Ordering::SeqCst);
             if key == 0 {
                 key = imp::create(self.dtor) as usize;
                 self.key.store(key, Ordering::SeqCst);
             }
-            INIT_LOCK.unlock();
             rtassert!(key != 0);
             return key
         }