cmslrucache.java

cms是开源的框架

            // remove the object from within the list
            theCacheObject.getPreviousLruObject().setNextLruObject(theCacheObject.getNextLruObject());
            theCacheObject.getNextLruObject().setPreviousLruObject(theCacheObject.getPreviousLruObject());
        }

        // update cache stats. and notify the cached object
        decreaseCache(theCacheObject);

        return theCacheObject;
    }

    /**
     * Returns the count of all cached objects.<p>
     *
     * @return the count of all cached objects
     */
    public int size() {

        return m_objectCount;
    }

    /**
     * Returns a string representing the current state of the cache.<p>
     * @return a string representing the current state of the cache
     */
    public String toString() {

        StringBuffer buf = new StringBuffer();
        buf.append("max. costs: " + m_maxCacheCosts).append(", ");
        buf.append("avg. costs: " + m_avgCacheCosts).append(", ");
        buf.append("max. costs/object: " + m_maxObjectCosts).append(", ");
        buf.append("costs: " + m_objectCosts).append(", ");
        buf.append("count: " + m_objectCount);
        return buf.toString();
    }

    /**
     * Touch an existing object in this cache, in the sense that it's "last-recently-used" state
     * is updated.<p>
     *
     * @param theCacheObject the object being touched
     * @return true if an object was found and touched
     */
    public synchronized boolean touch(I_CmsLruCacheObject theCacheObject) {

        if (!isCached(theCacheObject)) {
            return false;
        }

        // only objects with cache costs < the max. allowed object cache costs can be cached!
        if ((m_maxObjectCosts != -1) && (theCacheObject.getLruCacheCosts() > m_maxObjectCosts)) {
            if (LOG.isInfoEnabled()) {
                LOG.info(Messages.get().getBundle().key(
                    Messages.LOG_CACHE_COSTS_TOO_HIGH_2,
                    new Integer(theCacheObject.getLruCacheCosts()),
                    new Integer(m_maxObjectCosts)));
            }
            remove(theCacheObject);
            return false;
        }

        // set the list pointers correct
        I_CmsLruCacheObject nextObj = theCacheObject.getNextLruObject();
        if (nextObj == null) {
            // case 1: the object is already at the head pos.
            return true;
        }
        I_CmsLruCacheObject prevObj = theCacheObject.getPreviousLruObject();
        if (prevObj == null) {
            // case 2: the object at the tail pos., remove it from the tail to put it to the front as the new head
            I_CmsLruCacheObject newTail = nextObj;
            newTail.setPreviousLruObject(null);
            m_listTail = newTail;
        } else {
            // case 3: the object is somewhere within the list, remove it to put it the front as the new head
            prevObj.setNextLruObject(nextObj);
            nextObj.setPreviousLruObject(prevObj);
        }

        // set the touched object as the new head in the linked list:
        I_CmsLruCacheObject oldHead = m_listHead;
        if (oldHead != null) {
            oldHead.setNextLruObject(theCacheObject);
            theCacheObject.setNextLruObject(null);
            theCacheObject.setPreviousLruObject(oldHead);
        }
        m_listHead = theCacheObject;

        return true;
    }

    /**
     * Clears this cache for finalization.<p>
     * @throws Throwable if something goes wring
     */
    protected void finalize() throws Throwable {

        try {
            clear();
        } catch (Throwable t) {
            // ignore
        }
        super.finalize();
    }

    /**
     * Adds a cache object as the new haed to the list of all cached objects in this cache.<p>
     *
     * @param theCacheObject the object being added as the new head to the list of all cached objects
     */
    private void addHead(I_CmsLruCacheObject theCacheObject) {

        // set the list pointers correct
        if (m_objectCount > 0) {
            // there is at least 1 object already in the list
            I_CmsLruCacheObject oldHead = m_listHead;
            oldHead.setNextLruObject(theCacheObject);
            theCacheObject.setPreviousLruObject(oldHead);
            m_listHead = theCacheObject;
        } else {
            // it is the first object to be added to the list
            m_listTail = theCacheObject;
            m_listHead = theCacheObject;
            theCacheObject.setPreviousLruObject(null);
        }
        theCacheObject.setNextLruObject(null);

        // update cache stats. and notify the cached object
        increaseCache(theCacheObject);
    }

    /**
     * Decrease this caches statistics
     * and notify the cached object that it was removed from this cache.<p>
     *
     * @param theCacheObject the object being notified that it was removed from the cache
     */
    private void decreaseCache(I_CmsLruCacheObject theCacheObject) {

        // notify the object that it was now removed from the cache
        //theCacheObject.notify();
        theCacheObject.removeFromLruCache();

        // set the list pointers to null
        theCacheObject.setNextLruObject(null);
        theCacheObject.setPreviousLruObject(null);

        // update the cache stats.
        m_objectCosts -= theCacheObject.getLruCacheCosts();
        m_objectCount--;
    }

    /**
     * Removes the last recently used objects from the list of all cached objects as long
     * as the costs of all cached objects are higher than the allowed avg. costs of the cache.<p>
     */
    private void gc() {

        I_CmsLruCacheObject currentObject = m_listTail;
        while (currentObject != null) {
            if (m_objectCosts < m_avgCacheCosts) {
                break;
            }
            currentObject = currentObject.getNextLruObject();
            removeTail();
        }

    }

    /**
     * Increase this caches statistics 
     * and notify the cached object that it was added to this cache.<p>
     *
     * @param theCacheObject the object being notified that it was added to the cache
     */
    private void increaseCache(I_CmsLruCacheObject theCacheObject) {

        // notify the object that it was now added to the cache
        //theCacheObject.notify();
        theCacheObject.addToLruCache();

        // update the cache stats.
        m_objectCosts += theCacheObject.getLruCacheCosts();
        m_objectCount++;
    }

    /**
     * Test if a given object resides inside the cache.<p>
     *
     * @param theCacheObject the object to test 
     * @return true if the object is inside the cache, false otherwise
     */
    private boolean isCached(I_CmsLruCacheObject theCacheObject) {

        if (theCacheObject == null || m_objectCount == 0) {
            // the cache is empty or the object is null (which is never cached)
            return false;
        }

        I_CmsLruCacheObject nextObj = theCacheObject.getNextLruObject();
        I_CmsLruCacheObject prevObj = theCacheObject.getPreviousLruObject();

        if ((nextObj != null) || (prevObj != null)) {
            // the object has either a predecessor or successor in the linked 
            // list of all cached objects, so it is inside the cache
            return true;
        }

        if ((nextObj == null) && (prevObj == null)) {
            if ((m_objectCount == 1)
                && (m_listHead != null)
                && (m_listTail != null)
                && m_listHead.equals(theCacheObject)
                && m_listTail.equals(theCacheObject)) {
                // the object is the one and only object in the cache
                return true;
            }
        }

        return false;
    }

    /**
     * Removes the tailing object from the list of all cached objects.<p>
     */
    private synchronized void removeTail() {

        I_CmsLruCacheObject oldTail = m_listTail;
        if (oldTail != null) {
            I_CmsLruCacheObject newTail = oldTail.getNextLruObject();

            // set the list pointers correct
            if (newTail != null) {
                // there are still objects remaining in the list
                newTail.setPreviousLruObject(null);
                m_listTail = newTail;
            } else {
                // we removed the last object from the list
                m_listTail = null;
                m_listHead = null;
            }

            // update cache stats. and notify the cached object
            decreaseCache(oldTail);
        }
    }
}