UnownedLocal of Harmony Foundation reduces RC overhead (Basic knowledge of HarmonyOS HarmonyOS development)

What is UnownedLocal?

Annotate methods or individual local variables.
Annotating a single local variable means to exclude instance references of this variable from the reference count. Annotating a method means revoking the method's ownership of all local variables (explicit or implicit) of the referenced object, and excluding references to these variables from the reference count of the referenced object.

The purpose of UnownedLocal is to reduce RC overhead, not to eliminate circular references.

For the unsafe HashMap.containsValue method in multithreaded mode, other threads are not allowed to modify the HashMap synchronously. Therefore, the reading of internal tables and nodes in HashMap is not included in the reference count, so the referenced objects will not be released. In this case, you can use UnownedLocal to annotate the object in the method.

   @UnownedLocal
   public boolean containsValue(Object value) {
       Node<K,V>[] tab;
       V v;
       if ((tab = table) != null && size > 0) {
           for (int i = 0; i < tab.length; ++i) {
               for (Node<K,V> e = tab[i]; e != null; e = e.next) {
                   if ((v = e.value) == value || (value != null && value.equals(v)))
                   return true;
               }
           }
       }
       return false;
   }
 
   public boolean containsValue(Object value) {
       Node<K,V>[] @Unowned tab;
       V @Unowned v;
       if ((tab = table) != null && size > 0) {
           for (int i = 0; i < tab.length; ++i) {
               for (Node<K,V> e = tab[i]; e != null; e = e.next) {
                   if ((v = e.value) == value || (value != null && value.equals(v)))
                       return true;
               }
           }
       }
       return false;
   }
 

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Start from scratch to learn HarmonyOS Hongmeng 2.0 development

• Original HarmonyOS Hongmeng Getting Started Tutorial 01 Basic Environment and Development Tools (tutorial includes source code)
• Original HarmonyOS Hongmeng Development 02 Development Tools Installation
• Original HarmonyOS Hongmeng Getting Started Tutorial 03 Run the development tool to complete the basic configuration DevEco Studio (tutorial includes source code)
• Original HarmonyOS Hongmeng Development 04 Run the first hello world (tutorial with source code)
• Original HarmonyOS Hongmeng Development 05 Run the first page (tutorial with source code)
• Original HarmonyOS Hongmeng Development 06 Create page Feature Ability through code (tutorial includes source code)
• Original HarmonyOS Hongmeng Development 07 Programming to realize page jump (tutorial includes source code)