Optimise cypclass lock implementation assuming block acquisition semantics

Cython/Utility/CyObjects.cpp

@@ -79,36 +79,16 @@
                 }
 
                 void CyObject_UNRLOCK() const {
-                    int retry = 0;
-                    while (true) {
-                        uint32_t prev_readers = _readers;
-                        if (prev_readers + 1 > 1) {
-                            uint32_t new_readers = prev_readers - 1;
-                            if (_readers.compare_exchange_weak(prev_readers, new_readers)) {
-                                return;
-                            }
-                        }
-                        else {
-                            return;
-                        }
-
-                        retry++;
-                        if (retry > RETRY_THRESHOLD) {
-                            retry = 0;
-                            std::this_thread::yield();
-                        }
-                    }
+                    _readers.fetch_sub(1);
                 }
 
                 void CyObject_WLOCK() const {
                     int retry = 0;
                     while (true) {
-                        uint32_t prev_readers = _readers;
-                        if (prev_readers == 0) {
+                        uint32_t prev_readers = 0;
                         if (_readers.compare_exchange_weak(prev_readers, HAS_WRITER)) {
                             return;
                         }
-                        }
 
                         retry++;
                         if (retry > RETRY_THRESHOLD) {
@@ -124,8 +104,7 @@
                 }
 
                 void CyObject_UNWLOCK() const {
-                     uint32_t prev_readers = HAS_WRITER;
-                    _readers.compare_exchange_strong(prev_readers, 0);
+                    _readers.store(0);
                 }
         };