1 files changed, 49 insertions, 0 deletions
diff --git a/Src/nu/simple_rwlock.h b/Src/nu/simple_rwlock.h
new file mode 100644
index 00000000..f9952959
--- /dev/null
+++ b/Src/nu/simple_rwlock.h
@@ -0,0 +1,49 @@
+#pragma once
+
+/* 
+Simple Reader/Writer lock.  Lets unlimited readers through but a writer will lock exclusively
+not meant for high-throughput uses
+this is useful when writes are very infrequent
+*/
+#include <bfc/platform/types.h>
+#include <windows.h>
+
+typedef size_t simple_rwlock_t;
+static const size_t simple_rwlock_writer_active = 1; // writer active flag
+static const size_t simple_rwlock_reader_increment= 2; // to adjust reader count
+
+static inline void simple_rwlock_write_lock(simple_rwlock_t *lock)
+{
+	while (InterlockedCompareExchangePointer((PVOID volatile*)lock, (PVOID)simple_rwlock_writer_active, 0))
+	{
+		// nop
+	}
+}
+
+static inline void simple_rwlock_write_unlock(simple_rwlock_t *lock)
+{
+#ifdef _WIN64
+	InterlockedExchangeAdd64((LONGLONG  volatile*)lock, -simple_rwlock_writer_active);
+#else
+	InterlockedExchangeAdd((LONG volatile*)lock, -simple_rwlock_writer_active);
+#endif
+}
+
+
+static inline void simple_rwlock_read_lock(simple_rwlock_t *lock)
+{
+	InterlockedExchangeAdd((LONG volatile*)lock, simple_rwlock_reader_increment);
+	while ((*lock & simple_rwlock_writer_active))
+	{
+		// nope
+	}
+}
+
+static inline void simple_rwlock_read_unlock(simple_rwlock_t *lock)
+{
+	#ifdef _WIN64
+	InterlockedExchangeAdd64((LONGLONG  volatile*)lock, -simple_rwlock_reader_increment);
+#else
+	InterlockedExchangeAdd((LONG volatile*)lock, -simple_rwlock_reader_increment);
+#endif
+}