std: use `sync::Mutex` for internal statics

1 files changed, 12 insertions, 15 deletions

diff --git a/library/std/src/thread/mod.rs b/library/std/src/thread/mod.rs
index 55110c44b6e..0a51e1a10f4 100644
--- a/library/std/src/thread/mod.rs
+++ b/library/std/src/thread/mod.rs
@@ -1118,24 +1118,21 @@ impl ThreadId {
                     }
                 }
             } else {
-                use crate::sys_common::mutex::StaticMutex;
+                use crate::sync::{Mutex, PoisonError};
 
-                // It is UB to attempt to acquire this mutex reentrantly!
-                static GUARD: StaticMutex = StaticMutex::new();
-                static mut COUNTER: u64 = 0;
+                static COUNTER: Mutex<u64> = Mutex::new(0);
 
-                unsafe {
-                    let guard = GUARD.lock();
+                let mut counter = COUNTER.lock().unwrap_or_else(PoisonError::into_inner);
+                let Some(id) = counter.checked_add(1) else {
+                    // in case the panic handler ends up calling `ThreadId::new()`,
+                    // avoid reentrant lock acquire.
+                    drop(counter);
+                    exhausted();
+                };
 
-                    let Some(id) = COUNTER.checked_add(1) else {
-                        drop(guard); // in case the panic handler ends up calling `ThreadId::new()`, avoid reentrant lock acquire.
-                        exhausted();
-                    };
-
-                    COUNTER = id;
-                    drop(guard);
-                    ThreadId(NonZeroU64::new(id).unwrap())
-                }
+                *counter = id;
+                drop(counter);
+                ThreadId(NonZeroU64::new(id).unwrap())
             }
         }
     }