root/core/QCache.cpp

DEFINITIONS

1. m_max
2. flush
3. resize
4. add
5. validate

/* ***** BEGIN LICENSE BLOCK *****
 * Version: MPL 1.1/GPL 2.0/LGPL 2.1
 *
 * The contents of this file are subject to the Mozilla Public License Version
 * 1.1 (the "License"); you may not use this file except in compliance with
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 *
 * Software distributed under the License is distributed on an "AS IS" basis,
 * WITHOUT WARRANTY OF ANY KIND, either express or implied. See the License
 * for the specific language governing rights and limitations under the
 * License.
 *
 * The Original Code is [Open Source Virtual Machine.].
 *
 * The Initial Developer of the Original Code is
 * Adobe System Incorporated.
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 * the Initial Developer. All Rights Reserved.
 *
 * Contributor(s):
 *   Adobe AS3 Team
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 * either the GNU General Public License Version 2 or later (the "GPL"), or
 * the GNU Lesser General Public License Version 2.1 or later (the "LGPL"),
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#include "avmplus.h"

namespace avmplus
{
        using namespace MMgc;

        QCache::QCache(uint32_t _max, MMgc::GC* _gc) : 
                m_gc(_gc),
                m_head(NULL), 
                m_count(0), 
                m_max(0)
        { 
                MathUtils::RandomFastInit(&m_rand);
                resize(_max);
        }
        
        QCache::~QCache()
        {
                flush();
        }

        void QCache::flush() 
        {
                QCachedItem* gen = first();
                while (gen)
                {
                        QCachedItem* n = next(gen);
                        gen->next = NULL;
                        gen = n;
                }
                m_head = NULL;
                m_count = 0;
        }

        void QCache::resize(uint32_t _max) 
        {
                flush();
                // 0 -> unlimited
                m_max = !_max ? 0xffffffff : _max;
        }

        QCachedItem* QCache::add(QCachedItem* gen) 
        { 
                AvmAssert(gen && !next(gen));
                
                QCachedItem* evicted = NULL;
                
                // if no space, evict oldest
                if (m_count >= m_max)
                {
                        AvmAssert(m_count == m_max);
                        uint32_t which = MathUtils::Random(count(), &m_rand);
                        QCachedItem* evicted_prev = NULL;
                        for (QCachedItem* td = first(); td; td = next(td))
                        {
                                if (!which--)
                                {
                                        evicted = td;
                                        break;
                                }
                                evicted_prev = td;
                        }
                        if (evicted_prev)
                        {
                                evicted = evicted_prev->next;
                                AvmAssert(evicted != NULL && evicted != gen);
                                WB(m_gc, evicted_prev, &evicted_prev->next, evicted->next);
                        }
                        else
                        {
                                evicted = m_head;
                                AvmAssert(evicted != NULL && evicted != gen);
                                WB(m_gc, this, &m_head, evicted->next);
                        }
                        evicted->next = NULL;   // never need a WB to write NULL
                        --m_count;
                        #ifdef QCACHE_DEBUG
                        validate();
                        #endif
                }
                
                // add at head
                WB(m_gc, gen, &gen->next, m_head);
                WB(m_gc, this, &m_head, gen);
                ++m_count;
                                
                #ifdef QCACHE_DEBUG
                validate();
                #endif
                
                AvmAssert(evicted ? evicted->next == NULL : true);
                return evicted;
        }
        
        #ifdef QCACHE_DEBUG
        void QCache::validate() const
        {
                if (!m_head) 
                {
                        AvmAssert(m_count == 0);
                        return;
                }
                uint32_t c = 0;
                QCachedItem* prev = NULL;
                for (QCachedItem* td = first(); td; td = next(td))
                {
                        AvmAssert(prev ? prev->next == td : true);
                        ++c;
                        prev = td;
                        if (c > m_max)
                        {
                                // oops, probably a cycle, busted code
                                AvmAssert(0);
                        }
                }
                AvmAssert(c == m_count);
        }
        #endif
}