more cleanup

Author: SchrodingerZhu

libc/src/__support/threads/linux/callonce.h

@@ -27,27 +27,27 @@ LIBC_INLINE bool callonce_fastpath(CallOnceFlag *flag) {
   return flag->load(cpp::MemoryOrder::RELAXED) == FINISH;
 }
 
-[[gnu::noinline]]
-LIBC_INLINE int callonce_slowpath(CallOnceFlag *flag, void (*func)(void)) {
+template <class CallOnceCallback>
+[[gnu::noinline]] int callonce_slowpath(CallOnceFlag *flag,
+                                        CallOnceCallback callback) {
+
   auto *futex_word = reinterpret_cast<Futex *>(flag);
 
   FutexWordType not_called = NOT_CALLED;
 
   // The call_once call can return only after the called function |func|
   // returns. So, we use futexes to synchronize calls with the same flag value.
   if (futex_word->compare_exchange_strong(not_called, START)) {
-    func();
+    callback();
     auto status = futex_word->exchange(FINISH);
     if (status == WAITING)
       futex_word->notify_all();
     return 0;
   }
 
   FutexWordType status = START;
-  if (futex_word->compare_exchange_strong(status, WAITING) ||
-      status == WAITING) {
+  if (futex_word->compare_exchange_strong(status, WAITING) || status == WAITING)
     futex_word->wait(WAITING);
-  }
 
   return 0;
 }