fix: possible race condition extending native class

Author: edusperoni

NativeScript/runtime/ClassBuilder.cpp

@@ -2,27 +2,34 @@
 
 namespace tns {
 
-// Moved this method in a separate .cpp file because ARC destroys the class created with objc_allocateClassPair
-// when the control leaves this method scope
+// Moved this method in a separate .cpp file because ARC destroys the class
+// created with objc_allocateClassPair when the control leaves this method scope
 
-Class ClassBuilder::GetExtendedClass(std::string baseClassName, std::string staticClassName) {
-    Class baseClass = objc_getClass(baseClassName.c_str());
-    std::string name = !staticClassName.empty() ? staticClassName : baseClassName + "_" + std::to_string(++ClassBuilder::classNameCounter_);
-    Class clazz = objc_getClass(name.c_str());
+Class ClassBuilder::GetExtendedClass(std::string baseClassName,
+                                     std::string staticClassName) {
+  Class baseClass = objc_getClass(baseClassName.c_str());
+  std::string name =
+      !staticClassName.empty()
+          ? staticClassName
+          : baseClassName + "_" +
+                std::to_string(++ClassBuilder::classNameCounter_);
+  // here we could either call objc_getClass with the name to see if the class
+  // already exists or we can just try allocating it, which will return nil if
+  // the class already exists so we try allocating it every time to avoid race
+  // conditions in case this method is being executed by multiple threads
+  Class clazz = objc_allocateClassPair(baseClass, name.c_str(), 0);
 
-    if (clazz != nil) {
-        int i = 1;
-        std::string initialName = name;
-        while (clazz != nil) {
-            name = initialName + std::to_string(i++);
-            clazz = objc_getClass(name.c_str());
-        }
+  if (clazz != nil) {
+    int i = 1;
+    std::string initialName = name;
+    while (clazz != nil) {
+      name = initialName + std::to_string(i++);
+      clazz = objc_allocateClassPair(baseClass, name.c_str(), 0);
     }
+  }
 
-    clazz = objc_allocateClassPair(baseClass, name.c_str(), 0);
-
-    objc_registerClassPair(clazz);
-    return clazz;
+  objc_registerClassPair(clazz);
+  return clazz;
 }
 
-}
+}  // namespace tns