src/filters/BaseClasses/cache.h

   1 //------------------------------------------------------------------------------
   2 // File: Cache.h
   3 //
   4 // Desc: DirectShow base classes - efines a non-MFC generic cache class.
   5 //
   6 // Copyright (c) 1992-2002 Microsoft Corporation.  All rights reserved.
   7 //------------------------------------------------------------------------------
   8
   9
  10 /* This class implements a simple cache. A cache object is instantiated
  11    with the number of items it is to hold. An item is a pointer to an
  12    object derived from CBaseObject (helps reduce memory leaks). The cache
  13    can then have objects added to it and removed from it. The cache size
  14    is fixed at construction time and may therefore run out or be flooded.
  15    If it runs out it returns a NULL pointer, if it fills up it also returns
  16    a NULL pointer instead of a pointer to the object just inserted */
  17
  18 /* Making these classes inherit from CBaseObject does nothing for their
  19    functionality but it allows us to check there are no memory leaks */
  20
  21 /* WARNING Be very careful when using this class, what it lets you do is
  22    store and retrieve objects so that you can minimise object creation
  23    which in turns improves efficiency. However the object you store is
  24    exactly the same as the object you get back which means that it short
  25    circuits the constructor initialisation phase. This means any class
  26    variables the object has (eg pointers) are highly likely to be invalid.
  27    Therefore ensure you reinitialise the object before using it again */
  28
  29
  30 #ifndef __CACHE__
  31 #define __CACHE__
  32
  33
  34 class CCache : CBaseObject {
  35
  36     /* Make copy constructor and assignment operator inaccessible */
  37
  38     CCache(const CCache &refCache);
  39     CCache &operator=(const CCache &refCache);
  40
  41 private:
  42
  43     /* These are initialised in the constructor. The first variable points to
  44        an array of pointers, each of which points to a CBaseObject derived
  45        object. The m_iCacheSize is the static fixed size for the cache and the
  46        m_iUsed defines the number of places filled with objects at any time.
  47        We fill the array of pointers from the start (ie m_ppObjects[0] first)
  48        and then only add and remove objects from the end position, so in this
  49        respect the array of object pointers should be treated as a stack */
  50
  51     CBaseObject **m_ppObjects;
  52     const INT m_iCacheSize;
  53     INT m_iUsed;
  54
  55 public:
  56
  57     CCache(TCHAR *pName,INT iItems);
  58     virtual ~CCache();
  59
  60     /* Add an item to the cache */
  61     CBaseObject *AddToCache(CBaseObject *pObject);
  62
  63     /* Remove an item from the cache */
  64     CBaseObject *RemoveFromCache();
  65
  66     /* Delete all the objects held in the cache */
  67     void RemoveAll(void);
  68
  69     /* Return the cache size which is set during construction */
  70     INT GetCacheSize(void) const {return m_iCacheSize;};
  71 };
  72
  73 #endif /* __CACHE__ */
  74