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ReusableArenaBlock.hpp

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00001 /*
00002  * The Apache Software License, Version 1.1
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00004  *
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00008  * Redistribution and use in source and binary forms, with or without
00009  * modification, are permitted provided that the following conditions
00010  * are met:
00011  *
00012  * 1. Redistributions of source code must retain the above copyright
00013  *    notice, this list of conditions and the following disclaimer. 
00014  *
00015  * 2. Redistributions in binary form must reproduce the above copyright
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00019  *
00020  * 3. The end-user documentation included with the redistribution,
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00057 
00058 #if !defined(REUSABLEARENABLOCK_INCLUDE_GUARD_1357924680)
00059 #define REUSABLEARENABLOCK_INCLUDE_GUARD_1357924680
00060 
00061 
00062 
00063 #include <PlatformSupport/XalanBitmap.hpp>
00064 #include <PlatformSupport/ArenaBlock.hpp>
00065 
00066 
00067 
00068 
00069 template<class ObjectType>
00070 class ReusableArenaBlock : public ArenaBlock<ObjectType>
00071 {
00072 public:
00073 
00074     typedef ArenaBlock<ObjectType>              BaseClassType;
00075 
00076     typedef typename BaseClassType::size_type   size_type;
00077 
00078     /*
00079      * Construct an ArenaBlock of the specified size
00080      * of objects.
00081      *
00082      * @param theBlockSize The size of the block (the number of objects it can contain).
00083      */
00084     ReusableArenaBlock(size_type    theBlockSize) :
00085         BaseClassType(theBlockSize),
00086         m_freeList(theBlockSize),
00087         m_freeBlockCount(0)
00088     {
00089     }
00090 
00091     ~ReusableArenaBlock()
00092     {
00093         // Note that this-> is required by template lookup rules.
00094         this->destroyAll();
00095     }
00096 
00097     /*
00098      * Allocate a block.  Once the object is constructed, you must call
00099      * commitAllocation().
00100      *
00101      * @return a pointer to the new block.
00102      */
00103     virtual ObjectType*
00104     allocateBlock()
00105     {
00106         if (m_freeBlockCount == 0)
00107         {
00108             return BaseClassType::allocateBlock();
00109         }
00110         else
00111         {
00112             return getNextFromFreeList();
00113         }
00114     }
00115 
00116     /*
00117      * Commit the previous allocation.
00118      *
00119      * @param theBlock the address that was returned by allocateBlock()
00120      */
00121     virtual void
00122     commitAllocation(ObjectType*    theBlock)
00123     {
00124         assert(theBlock != 0);
00125         assert(m_freeBlockCount == 0 ||
00126                theBlock == getNextFromFreeList());
00127 
00128         if (m_freeBlockCount == 0)
00129         {
00130             BaseClassType::commitAllocation(theBlock);
00131         }
00132         else
00133         {
00134             removeFromFreeList(theBlock);
00135         }
00136     }
00137 
00138     /*
00139      * Find out if there is a block available.
00140      *
00141      * @return true if one is available, false if not.
00142      */
00143     virtual bool
00144     blockAvailable() const
00145     {
00146         return m_freeBlockCount != 0 ? true : BaseClassType::blockAvailable();
00147     }
00148 
00149     /*
00150      * Get the number of objects currently allocated in the
00151      * block.
00152      *
00153      * @return The number of objects allocated.
00154      */
00155     virtual size_type
00156     getCountAllocated() const
00157     {
00158         return BaseClassType::getCountAllocated() - m_freeBlockCount;
00159     }
00160 
00161     /*
00162      * Determine if this block owns the specified object.  Note
00163      * that even if the object address is within our block, this
00164      * call will return false if no object currently occupies the
00165      * block.  See also ownsBlock().
00166      *
00167      * @param theObject the address of the object.
00168      * @return true if we own the object, false if not.
00169      */
00170     virtual bool
00171     ownsObject(const ObjectType*    theObject) const
00172     {
00173         return BaseClassType::ownsObject(theObject) && !isOnFreeList(theObject);
00174     }
00175 
00176     /*
00177      * Destroy the object, and return the block to the free list.
00178      * The behavior is undefined if the object pointed to is not
00179      * owned by the block.
00180      *
00181      * @param theObject the address of the object.
00182      */
00183     void
00184     destroyObject(ObjectType*   theObject)
00185     {
00186         assert(ownsObject(theObject) == true);
00187 
00188         m_destroyFunction(*theObject);
00189 
00190         addToFreeList(theObject);
00191     }
00192 
00193 protected:
00194 
00195     /*
00196      * Determine if the block should be destroyed.  Returns true,
00197      * unless the object is on the free list.  The behavior is
00198      * undefined if the object pointed to is not owned by the
00199      * block.
00200      *
00201      * @param theObject the address of the object
00202      * @return true if block should be destroyed, false if not.
00203      */
00204     virtual bool
00205     shouldDestroyBlock(const ObjectType*    theObject) const
00206     {
00207         return !isOnFreeList(theObject);
00208     }
00209 
00210 private:
00211 
00212     // Not implemented...
00213     ReusableArenaBlock(const ReusableArenaBlock<ObjectType>&);
00214 
00215     ReusableArenaBlock<ObjectType>&
00216     operator=(const ReusableArenaBlock<ObjectType>&);
00217 
00218     bool
00219     operator==(const ReusableArenaBlock<ObjectType>&) const;
00220 
00221 
00222     /*
00223      * Determine if the block is on the free list.  The behavior is
00224      * undefined if the object pointed to is not owned by the
00225      * block.
00226      *
00227      * @param theObject the address of the object
00228      * @return true if block is on the free list, false if not.
00229      */
00230     bool
00231     isOnFreeList(const ObjectType*  theObject) const
00232     {
00233         if (m_freeBlockCount == 0)
00234         {
00235             return false;
00236         }
00237         else
00238         {
00239             const size_type     theOffset =
00240                     getBlockOffset(theObject);
00241 
00242             return m_freeList.isSet(theOffset);
00243         }
00244     }
00245 
00246     /*
00247      * Add a block to the free list.  The behavior is
00248      * undefined if the object pointed to is not owned by the
00249      * block.
00250      *
00251      * @param theObject the address of the object
00252      */
00253     void
00254     addToFreeList(const ObjectType*     theObject)
00255     {
00256         const size_type     theOffset =
00257                 getBlockOffset(theObject);
00258 
00259         m_freeList.set(theOffset);
00260 
00261         ++m_freeBlockCount;
00262     }
00263 
00264     /*
00265      * Remove a block from the free list.  The behavior is
00266      * undefined if the object pointed to is not owned by the
00267      * block.
00268      *
00269      * @param theObject the address of the object
00270      */
00271     void
00272     removeFromFreeList(const ObjectType*    theObject)
00273     {
00274         const size_type     theOffset =
00275                 getBlockOffset(theObject);
00276 
00277         m_freeList.clear(theOffset);
00278 
00279         --m_freeBlockCount;
00280     }
00281 
00282     /*
00283      * Get the next block from the free list.  Returns 0 if
00284      * the free list is empty.
00285      *
00286      * @return the address of the block
00287      */
00288     ObjectType*
00289     getNextFromFreeList()
00290     {
00291         ObjectType*     theResult = 0;
00292 
00293         if (m_freeBlockCount > 0)
00294         {
00295             const size_type     theFreeListSize = m_freeList.getSize();
00296 
00297             for(size_type i = 0; i < theFreeListSize; ++i)
00298             {
00299                 if (m_freeList.isSet(i) == true)
00300                 {
00301                     // Note that this-> is required by template lookup rules.
00302                     theResult = this->getBlockAddress(i);
00303 
00304                     break;
00305                 }
00306             }
00307         }
00308 
00309         return theResult;
00310     }
00311 
00312     // Bitmap which tracks which blocks are not in use
00313     // and that should not be destroyed.
00314     XalanBitmap     m_freeList;
00315 
00316     // The number of blocks on the free list.)
00317     size_type       m_freeBlockCount;
00318 };
00319 
00320 
00321 
00322 #endif  // !defined(REUSABLEARENABLOCK_INCLUDE_GUARD_1357924680)

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