+
+/// \brief A thread-safe version of \c llvm::RefCountedBase.
+///
+/// A generic base class for objects that wish to have their lifetimes managed
+/// using reference counts. Classes subclass \c ThreadSafeRefCountedBase to
+/// obtain such functionality, and are typically handled with
+/// \c IntrusiveRefCntPtr "smart pointers" which automatically handle the
+/// management of reference counts.
+template <class Derived>
+class ThreadSafeRefCountedBase {
+ mutable std::atomic<int> RefCount;
+
+protected:
+ ThreadSafeRefCountedBase() : RefCount(0) {}
+
+public:
+ void Retain() const { ++RefCount; }
+
+ void Release() const {
+ int NewRefCount = --RefCount;
+ assert(NewRefCount >= 0 && "Reference count was already zero.");
+ if (NewRefCount == 0)
+ delete static_cast<const Derived*>(this);
+ }
+};