Merge pull request #64795 from RandomShaper/fix_saferefcount

Prevent misuse of SafeRefCount

core/templates/safe_refcount.h

@@ -33,6 +33,10 @@
 
 #include "core/typedefs.h"
 
+#ifdef DEV_ENABLED
+#include "core/error/error_macros.h"
+#endif
+
 #include <atomic>
 #include <type_traits>
 
@@ -163,6 +167,16 @@ public:
 class SafeRefCount {
 	SafeNumeric<uint32_t> count;
 
+#ifdef DEV_ENABLED
+	_ALWAYS_INLINE_ void _check_unref_sanity() {
+		// This won't catch every misuse, but it's better than nothing.
+		CRASH_COND_MSG(count.get() == 0,
+				"Trying to unreference a SafeRefCount which is already zero is wrong and a symptom of it being misused.\n"
+				"Upon a SafeRefCount reaching zero any object whose lifetime is tied to it, as well as the ref count itself, must be destroyed.\n"
+				"Moreover, to guarantee that, no multiple threads should be racing to do the final unreferencing to zero.");
+	}
+#endif
+
 public:
 	_ALWAYS_INLINE_ bool ref() { // true on success
 		return count.conditional_increment() != 0;
@@ -173,10 +187,16 @@ public:
 	}
 
 	_ALWAYS_INLINE_ bool unref() { // true if must be disposed of
+#ifdef DEV_ENABLED
+		_check_unref_sanity();
+#endif
 		return count.decrement() == 0;
 	}
 
 	_ALWAYS_INLINE_ uint32_t unrefval() { // 0 if must be disposed of
+#ifdef DEV_ENABLED
+		_check_unref_sanity();
+#endif
 		return count.decrement();
 	}