1. Astobj2
Joshua Colp, Senior Software Developer 1 1

2. The Past Previously no consistent full featured object API
Basic linked list container existed
Inconsistent locking
Fragile object destruction 2 2

3. The Present Reference counted objects
Containers (hash or linked list, optional)
Iterators
Callbacks
Container cloning
Recommended for new development when applicable
Unit tested 3 3

4. Objects API calls: ao2_alloc, ao2_ref
Reference counted (integer stored in object)
Destructor callback called when count of 0 is reached
Optionally stored in containers
Optional locking (mutex, read/write, none) 4 4

5. Global Objects
API calls: ao2_global_obj_release, ao2_global_obj_replace_unref
Global storage area for an object
Object can be replaced at any time
Storage area protected by lock
Used by configuration framework 5 5

6. Containers API calls: ao2_container_alloc, ao2_link, ao2_unlink
Bucket size for object distribution
User provided hashing callback
User provided comparison callback
Linked list used for collisions, thus bucket size of 1 is a linked list
Is itself a reference counted ao2 object 6 6

7. Iterators
API calls: ao2_iterator_init, ao2_iterator_next, ao2_iterator_destroy
Container traversal
Does not keep container locked
Does not require separate function for logic
Must remember to release reference to object
Like iterating a linked list 7 7

8. Callbacks API call: ao2_callback
Keeps container locked for each execution
Executes function on object(s), can perform matching or general logic
Flags to control behavior (unlink if matched, allow multiple objects, key for specific object)
Can return object matched 8 8

9. Finding Objects API call: ao2_find Uses callback internally
Can specify a key or pointer to object for comparison
Returns object with reference count increased 9 9

10. Resource Acquisition Is Initialization
Macro: RAII_VAR
Useful when increasing an object reference count
Can decrease reference count automatically when variable goes out of scope
Reduces chance of reference count leaks 10 10

11. Cloning API call: ao2_container_clone Uses callback internally
Creates new duplicate container
Creates copies of node objects, can be expensive, objects not copied itself 11 11

12. Potential Problems Reference count leaks, object not getting destroyed
Circular references, multiple objects not getting destroyed
Inefficient hashing algorithm, decreased performance 12 12

13. Learn More Include/asterisk/astobj2.h
ence+Count+Debugging
Simple example is main/cel.c
Used everywhere, though. 13 13