src/xalanc/PlatformSupport/ReusableArenaBlock.hpp

/*
 * Licensed to the Apache Software Foundation (ASF) under one
 * or more contributor license agreements. See the NOTICE file
 * distributed with this work for additional information
 * regarding copyright ownership. The ASF licenses this file
 * to you under the Apache License, Version 2.0 (the  "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

#if !defined(REUSABLEARENABLOCK_INCLUDE_GUARD_1357924680)
#define REUSABLEARENABLOCK_INCLUDE_GUARD_1357924680


#include <xalanc/PlatformSupport/ArenaBlockBase.hpp>



#include <xalanc/Include/XalanMemMgrAutoPtr.hpp>



namespace XALAN_CPP_NAMESPACE {



template <class ObjectType,
#if defined(XALAN_NO_DEFAULT_TEMPLATE_ARGUMENTS)
         class SizeType>
#else
         class SizeType = unsigned short>
#endif
class ReusableArenaBlock : public ArenaBlockBase<ObjectType, SizeType>
{

public:

    typedef ArenaBlockBase<ObjectType, SizeType>        BaseClassType;

    typedef typename BaseClassType::size_type           size_type;

    typedef ReusableArenaBlock<ObjectType, SizeType>    ThisType;

    struct NextBlock
    {
        enum { VALID_OBJECT_STAMP = 0xffddffdd };

        size_type       next;
        const int       verificationStamp;
        
        NextBlock( size_type _next):
            next(_next),
            verificationStamp(VALID_OBJECT_STAMP)
        {
        }

        bool
        isValidFor( size_type  rightBorder ) const
        {
            return ( ( verificationStamp == int(VALID_OBJECT_STAMP)) &&
                ( next <= rightBorder ) ) ? true : false ;
        }
    };

    /*
     * Construct an ArenaBlock of the specified size
     * of objects.
     *
     * @param theBlockSize The size of the block (the
     * number of objects it can contain).
     */
    ReusableArenaBlock(
                MemoryManager&  theManager,
                size_type           theBlockSize) :
        BaseClassType(theManager, theBlockSize),
        m_firstFreeBlock(0),
        m_nextFreeBlock(0)

    {
        XALAN_STATIC_ASSERT(sizeof(ObjectType) >= sizeof(NextBlock));
        
        for( size_type i = 0; i < this->m_blockSize; ++i )
        {
            new (&this->m_objectBlock[i]) NextBlock(size_type(i + 1));
        }
    }

    ~ReusableArenaBlock()
    {
        size_type removedObjects = 0;

        for (size_type i = 0;
                i < this->m_blockSize &&
                removedObjects < this->m_objectCount;
                    ++i)
        {
            if ( isOccupiedBlock(&this->m_objectBlock[i]) )
            {
                this->m_objectBlock[i].~ObjectType();

                ++removedObjects;
            }
        }
    }

    static ThisType*
    create(
                MemoryManager&  theManager,
                size_type           theBlockSize)
    {
        ThisType* theInstance;

        return XalanConstruct(
                    theManager,
                    theInstance,
                    theManager,
                    theBlockSize);
    }

    /*
     * Allocate a block.  Once the object is constructed, you must call
     * commitAllocation().
     *
     * @return a pointer to the new block.
     */
    ObjectType*
    allocateBlock()
    {
        if ( this->m_objectCount == this->m_blockSize )
        {
            assert ( this->m_firstFreeBlock == (this->m_blockSize + 1) );

            return 0;
        }
        else
        {
            assert( this->m_objectCount < this->m_blockSize );

            ObjectType*     theResult = 0;

            assert ( this->m_firstFreeBlock <= this->m_blockSize );
            assert ( this->m_nextFreeBlock <= this->m_blockSize );

            // check if any part was allocated but not commited
            if(this->m_firstFreeBlock != this->m_nextFreeBlock)
            {
                // return the previously allocated block and wait for a commit
                theResult = this->m_objectBlock + this->m_firstFreeBlock;
            }
            else
            {
                theResult = this->m_objectBlock + this->m_firstFreeBlock;

                assert(size_type(theResult - this->m_objectBlock) < this->m_blockSize);

                NextBlock* const    theBlock =
                    reinterpret_cast<NextBlock*>(theResult);

                this->m_nextFreeBlock = theBlock->next;

                assert(theBlock->isValidFor(this->m_blockSize));
                assert(this->m_nextFreeBlock <= this->m_blockSize);

                ++this->m_objectCount;
            }

            return theResult;
        }
    }

    /*
     * Commit the previous allocation.
     *
     * @param theBlock the address that was returned by allocateBlock()
     */
    void
    commitAllocation(ObjectType* /* theBlock */)
    {
        assert ( this->m_objectCount <= this->m_blockSize );

        this->m_firstFreeBlock = this->m_nextFreeBlock;
    }

    /*
     * Destroy the object, and return the block to the free list.
     * The behavior is undefined if the object pointed to is not
     * owned by the block.
     *
     * @param theObject the address of the object.
     */
    void
    destroyObject(ObjectType*   theObject)
    {
        assert(theObject != 0);

        // check if any uncommited block is there, add it to the list
        if ( this->m_firstFreeBlock != this->m_nextFreeBlock )
        {
            // Return it to the pool of free blocks
            void* const     p = this->m_objectBlock + this->m_firstFreeBlock;

            new (p) NextBlock(this->m_nextFreeBlock);

            this->m_nextFreeBlock = this->m_firstFreeBlock;
        }

        assert(ownsObject(theObject) == true);
        assert(shouldDestroyBlock(theObject));

        XalanDestroy(*theObject);

        new (theObject) NextBlock(this->m_firstFreeBlock);

        m_firstFreeBlock =
            this->m_nextFreeBlock =
            size_type(theObject - this->m_objectBlock);

        assert (this->m_firstFreeBlock <= this->m_blockSize);

        --this->m_objectCount;
    }

    /*
     * Determine if this block owns the specified object.  Note
     * that even if the object address is within our block, this
     * call will return false if no object currently occupies the
     * block.  See also ownsBlock().
     *
     * @param theObject the address of the object.
     * @return true if we own the object, false if not.
     */
    bool
    ownsObject(const ObjectType*    theObject) const
    {
        assert ( theObject != 0 );

        return isOccupiedBlock(theObject);
    }

protected:

    /*
     * Determine if the block should be destroyed.  Returns true,
     * unless the object is on the free list.  The behavior is
     * undefined if the object pointed to is not owned by the
     * block.
     *
     * @param theObject the address of the object
     * @return true if block should be destroyed, false if not.
     */
    bool
    shouldDestroyBlock(const ObjectType*    theObject) const
    {
        assert(size_type(theObject - this->m_objectBlock) < this->m_blockSize);

        return !isOnFreeList(theObject);
    }

    bool
    isOccupiedBlock(const ObjectType*    block) const
    {
        assert( block !=0 );

        return !(this->ownsBlock(block) &&
                 reinterpret_cast<const NextBlock*>(block)->isValidFor(this->m_blockSize));
    }

private:

    // Not implemented...
    ReusableArenaBlock(const ReusableArenaBlock<ObjectType, SizeType>&);

    ReusableArenaBlock<ObjectType, SizeType>&
    operator=(const ReusableArenaBlock<ObjectType, SizeType>&);

    bool
    operator==(const ReusableArenaBlock<ObjectType, SizeType>&) const;


    /*
     * Determine if the block is on the free list.  The behavior is
     * undefined if the object pointed to is not owned by the
     * block.
     *
     * @param theObject the address of the object
     * @return true if block is on the free list, false if not.
     */
    bool
    isOnFreeList(const ObjectType*  theObject) const
    {
        if ( this->m_objectCount == 0 )
        {
            return false;
        }
        else
        {
            ObjectType*     pRunPtr = this->m_objectBlock + this->m_firstFreeBlock;

            for (size_type i = 0;
                    i < this->m_blockSize - this->m_objectCount;
                        ++i)
            {
                assert(this->ownsBlock(pRunPtr));

                if (pRunPtr == theObject)
                {
                    return true;
                }
                else
                {
                    NextBlock* const    p = reinterpret_cast<NextBlock*>(pRunPtr);

                    assert(p->isValidFor(this->m_blockSize));

                    pRunPtr = this->m_objectBlock + p->next;
                }
            }

            return false;
        }
    }

    // Data members...
    size_type   m_firstFreeBlock;

    size_type   m_nextFreeBlock;
};



}



#endif  // !defined(REUSABLEARENABLOCK_INCLUDE_GUARD_1357924680)