.. role:: blue
   :class: blue

Garbage Collection in Cache Manager
===================================
.. _Garbage_collection_in_Cache_Manager_:

.. версия ядра: 

The cache manager :blue:`CacheManager` deletes unused caches at the first call from sequential code.

In addition, garbage collection runs automatically on exiting a parallel region.

The mathematical kernel provides an interface for clearing cached data – the :blue:`MbGarbageCollection` class.

The :blue:`MbGarbageCollection` class is the garbage collector which clears caches in registered objects of the :blue:`CacheCleaner` type. By request it deletes caches in the registered objects.

In order to enable garbage collection in an object of type :blue:`CacheCleaner`, the object needs to implement the :blue:`ResetCacheData`\() method for caches cleaning and to subscribe to garbage collection in the :blue:`MbGarbageCollection` class.

The :blue:`CacheManager` class is derived from the :blue:`CacheCleaner` class, which makes it possible to run caches clearing in :blue:`CacheManager` automatically. For that, when creating a cache for a thread the cache manager registers itself in the :blue:`MbGarbageCollection` class.

Base Class for Objects that Require Garbage Collection
------------------------------------------------------

In order to subscribe to garbage collection, a class should be derived from the :blue:`CacheCleaner` class and should implement the **ResetCacheData** method for deleting cached data.

:blue:`CacheCleaner` is the base class for objects that require garbage collection. It implements the methods:

- **void SubcribeOnCleaning()** – subscribe the object for garbage collection.
- **void UnsubcribeOnCleaning()** – unsubscribe the object from garbage collection.

The :blue:`CacheCleaner` class also defines the method:

- **bool ResetCacheData()** – reset cached data. Should return true if cached data was cleared and the object was unsubscribed from garbage collection.

Class MbGarbageCollection
-------------------------

The :blue:`MbGarbageCollection` class is the garbage collector for objects of type :blue:`CacheCleaner`, which keep cached data. By request :blue:`MbGarbageCollection` clears caches in registered objects by calling :blue:`ResetCacheData` for each object.

The :blue:`MbGarbageCollection` class implements the methods:

- **void Subscribe( CacheCleaner \* obj )** – subscribe the object to garbage collection.
- **void Unsubscribe( CacheCleaner \* obj )** – unsubscribe the object from garbage collection.
- **static bool Run( bool force = false )** – perform garbage collection. Should be called in sequential code. When called in a parallel region, does nothing. If force == false, then run garbage collection in caches created for threads which are finished; if force == true, then force garbage collection in all caches. Returns true if garbage collection is done.
- **static void Enable( bool allow = true )** – enable/disable collecting data for garbage collection. By default it is enabled.