From f286e3c8286714ac5c9053693f6d9a9fe86a4e15 Mon Sep 17 00:00:00 2001
From: cpplearner <cpplearner@outlook.com>
Date: Sat, 6 Dec 2025 08:37:15 +0800
Subject: [PATCH] `<mutex>`: Use `if constexpr` for `std::lock`&`std::try_lock`

---
 stl/inc/mutex | 65 +++++++++++++++++++++------------------------------
 1 file changed, 27 insertions(+), 38 deletions(-)

diff --git a/stl/inc/mutex b/stl/inc/mutex
index bebb43c264e..dfb23158dc4 100644
--- a/stl/inc/mutex
+++ b/stl/inc/mutex
@@ -343,30 +343,25 @@ int _Try_lock_range(const int _First, const int _Last, _LockN&... _LkN) {
     return -1;
 }
 
-template <class _Lock0, class _Lock1, class _Lock2, class... _LockN>
-int _Try_lock1(_Lock0& _Lk0, _Lock1& _Lk1, _Lock2& _Lk2, _LockN&... _LkN) { // try to lock 3 or more locks
-    return _Try_lock_range(0, sizeof...(_LockN) + 3, _Lk0, _Lk1, _Lk2, _LkN...);
-}
+_EXPORT_STD template <class _Lock0, class _Lock1, class... _LockN>
+_NODISCARD_TRY_CHANGE_STATE int try_lock(_Lock0& _Lk0, _Lock1& _Lk1, _LockN&... _LkN) { // try to lock multiple locks
+    if constexpr (sizeof...(_LockN) == 0) {
+        // try to lock 2 locks, special case for better codegen and reduced metaprogramming for common case
+        if (!_Lk0.try_lock()) {
+            return 0;
+        }
 
-template <class _Lock0, class _Lock1>
-int _Try_lock1(_Lock0& _Lk0, _Lock1& _Lk1) {
-    // try to lock 2 locks, special case for better codegen and reduced metaprogramming for common case
-    if (!_Lk0.try_lock()) {
-        return 0;
-    }
+        _Unlock_one_guard<_Lock0> _Guard{_Lk0};
+        if (!_Lk1.try_lock()) {
+            return 1;
+        }
 
-    _Unlock_one_guard<_Lock0> _Guard{_Lk0};
-    if (!_Lk1.try_lock()) {
-        return 1;
+        _Guard._Lk_ptr = nullptr;
+        return -1;
+    } else {
+        // try to lock 3 or more locks
+        return _Try_lock_range(0, sizeof...(_LockN) + 2, _Lk0, _Lk1, _LkN...);
     }
-
-    _Guard._Lk_ptr = nullptr;
-    return -1;
-}
-
-_EXPORT_STD template <class _Lock0, class _Lock1, class... _LockN>
-_NODISCARD_TRY_CHANGE_STATE int try_lock(_Lock0& _Lk0, _Lock1& _Lk1, _LockN&... _LkN) { // try to lock multiple locks
-    return _Try_lock1(_Lk0, _Lk1, _LkN...);
 }
 
 template <class... _LockN>
@@ -399,15 +394,6 @@ int _Lock_attempt(const int _Hard_lock, _LockN&... _LkN) {
     return _Failed;
 }
 
-template <class _Lock0, class _Lock1, class _Lock2, class... _LockN>
-void _Lock_nonmember1(_Lock0& _Lk0, _Lock1& _Lk1, _Lock2& _Lk2, _LockN&... _LkN) {
-    // lock 3 or more locks, without deadlock
-    int _Hard_lock = 0;
-    while (_Hard_lock != -1) {
-        _Hard_lock = _Lock_attempt(_Hard_lock, _Lk0, _Lk1, _Lk2, _LkN...);
-    }
-}
-
 template <class _Lock0, class _Lock1>
 bool _Lock_attempt_small(_Lock0& _Lk0, _Lock1& _Lk1) {
     // attempt to lock 2 locks, by first locking _Lk0, and then trying to lock _Lk1 returns whether to try again
@@ -424,16 +410,19 @@ bool _Lock_attempt_small(_Lock0& _Lk0, _Lock1& _Lk1) {
     return true;
 }
 
-template <class _Lock0, class _Lock1>
-void _Lock_nonmember1(_Lock0& _Lk0, _Lock1& _Lk1) {
-    // lock 2 locks, without deadlock, special case for better codegen and reduced metaprogramming for common case
-    while (_Lock_attempt_small(_Lk0, _Lk1) && _Lock_attempt_small(_Lk1, _Lk0)) { // keep trying
-    }
-}
-
 _EXPORT_STD template <class _Lock0, class _Lock1, class... _LockN>
 void lock(_Lock0& _Lk0, _Lock1& _Lk1, _LockN&... _LkN) { // lock multiple locks, without deadlock
-    _Lock_nonmember1(_Lk0, _Lk1, _LkN...);
+    if constexpr (sizeof...(_LockN) == 0) {
+        // lock 2 locks, without deadlock, special case for better codegen and reduced metaprogramming for common case
+        while (_Lock_attempt_small(_Lk0, _Lk1) && _Lock_attempt_small(_Lk1, _Lk0)) { // keep trying
+        }
+    } else {
+        // lock 3 or more locks, without deadlock
+        int _Hard_lock = 0;
+        while (_Hard_lock != -1) {
+            _Hard_lock = _Lock_attempt(_Hard_lock, _Lk0, _Lk1, _LkN...);
+        }
+    }
 }
 
 _EXPORT_STD template <class _Mutex>