Provide a lock-free reader-writer lock implementation

Cython/Utility/CyObjects.cpp

@@ -13,41 +13,121 @@
 
 #ifdef __cplusplus
     #if __cplusplus >= 201103L
+        #include <cstdint>
         #include <atomic>
+        #include <thread>
+        #include <type_traits>
+
         using namespace std;
+
         #define CyObject_ATOMIC_REFCOUNT_TYPE atomic_int
 
-        #include <pthread.h>
 
-        #include <sys/types.h>
+        class CyLock {
+            protected:
+                const uint32_t HAS_WRITER = 0xffffffff;
+                const int RETRY_THRESHOLD = 100;
+                std::atomic<uint32_t> _readers;
 
-        #include <unistd.h>
-        #include <sys/syscall.h>
-        #include <vector>
+            public:
+                CyLock() {
+                    _readers = 0;
+                }
 
-        #include <sstream>
-        #include <iostream>
-        #include <stdexcept>
+                void rlock(const char * context) {
+                    int retry = 0;
+                    while (true) {
+                        uint32_t prev_readers = _readers;
+                        if (prev_readers != HAS_WRITER) {
+                            uint32_t new_readers = prev_readers + 1;
+                            if (_readers.compare_exchange_weak(prev_readers, new_readers)) {
+                                return;
+                            }
+                        }
 
-        #include <type_traits>
+                        retry++;
+                        if (retry > RETRY_THRESHOLD) {
+                            retry = 0;
+                            std::this_thread::yield();
+                        }
+                    }
+                }
 
+                int tryrlock() {
+                    int retry = 0;
+                    while (true) {
+                        uint32_t prev_readers = _readers;
+                        if (prev_readers == HAS_WRITER) {
+                            return -1;
+                        }
+                        uint32_t new_readers = prev_readers + 1;
+                        if (_readers.compare_exchange_weak(prev_readers, new_readers)) {
+                            return 0;
+                        }
 
-        class CyLock {
-            protected:
-                pthread_rwlock_t rwlock;
-            public:
-                CyLock() {
-                    pthread_rwlock_init(&this->rwlock, NULL);
+                        retry++;
+                        if (retry > RETRY_THRESHOLD) {
+                            retry = 0;
+                            std::this_thread::yield();
+                        }
                     }
-                ~CyLock() {
-                    pthread_rwlock_destroy(&this->rwlock);
                 }
-                void wlock(const char * context);
-                void rlock(const char * context);
-                void unwlock();
-                void unrlock();
-                int tryrlock();
-                int trywlock();
+
+                void unrlock() {
+                    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();
+                        }
+                    }
+                }
+
+                void wlock(const char * context) {
+                    int retry = 0;
+                    while (true) {
+                        uint32_t prev_readers = _readers;
+                        if (prev_readers == 0) {
+                            if (_readers.compare_exchange_weak(prev_readers, HAS_WRITER)) {
+                                return;
+                            }
+                        }
+
+                        retry++;
+                        if (retry > RETRY_THRESHOLD) {
+                            retry = 0;
+                            std::this_thread::yield();
+                        }
+                    }
+                }
+
+                int trywlock() {
+                    uint32_t prev_readers = _readers;
+                    if (prev_readers == 0) {
+                        return _readers.compare_exchange_weak(prev_readers, HAS_WRITER) - 1;
+                    }
+                    return -1;
+                }
+
+                void unwlock() {
+                    uint32_t prev_readers = _readers;
+                    if (prev_readers == HAS_WRITER) {
+                        _readers.compare_exchange_weak(prev_readers, 0);
+                    }
+                    return;
+                }
         };
 
         struct CyPyObject {
@@ -517,31 +597,6 @@
 #endif /* __cplusplus */
 
 
-void CyLock::rlock(CYTHON_UNUSED const char *context) {
-    pthread_rwlock_rdlock(&this->rwlock);
-}
-
-int CyLock::tryrlock() {
-    return pthread_rwlock_tryrdlock(&this->rwlock);
-}
-
-void CyLock::unrlock() {
-    pthread_rwlock_unlock(&this->rwlock);
-}
-
-void CyLock::wlock(CYTHON_UNUSED const char *context) {
-    pthread_rwlock_wrlock(&this->rwlock);
-}
-
-int CyLock::trywlock() {
-    return pthread_rwlock_trywrlock(&this->rwlock);
-}
-
-void CyLock::unwlock() {
-    pthread_rwlock_unlock(&this->rwlock);
-}
-
-
 /*
  * Atomic counter increment and decrement implementation based on
  * @source: https://www.boost.org/doc/libs/1_73_0/doc/html/atomic/usage_examples.html