Package net.sf.ehcache.distribution

Class RMIAsynchronousCacheReplicator

  • All Implemented Interfaces:
    java.lang.Cloneable, CacheReplicator, CacheEventListener
    public class RMIAsynchronousCacheReplicator
extends RMISynchronousCacheReplicator
    Listens to CacheManager and Cache events and propagates those to CachePeer peers of the Cache asynchronously.

    Updates are guaranteed to be replicated in the order in which they are received.

    While much faster in operation than RMISynchronousCacheReplicator, it does suffer from a number of problems. Elements, which may be being spooled to DiskStore may stay around in memory because references are being held to them from EventMessages which are queued up. The replication thread runs once per second, limiting the build up. However a lot of elements can be put into a cache in that time. We do not want to get an OutOfMemoryError using distribution in circumstances when it would not happen if we were just using the DiskStore.

    Accordingly, the Element values in EventMessages are held by SoftReference in the queue, so that they can be discarded if required by the GC to avoid an OutOfMemoryError. A log message will be issued on each flush of the queue if there were any forced discards. One problem with GC collection of SoftReferences is that the VM (JDK1.5 anyway) will do that rather than grow the heap size to the maximum. The workaround is to either set minimum heap size to the maximum heap size to force heap allocation at start up, or put up with a few lost messages while the heap grows.

    Version:
    $Id$
    Author:
    Greg Luck

    • Constructor Detail

      • RMIAsynchronousCacheReplicator

        public RMIAsynchronousCacheReplicator​(boolean replicatePuts,
                                      boolean replicatePutsViaCopy,
                                      boolean replicateUpdates,
                                      boolean replicateUpdatesViaCopy,
                                      boolean replicateRemovals,
                                      int replicationInterval,
                                      int maximumBatchSize)
        Constructor for internal and subclass use

    • Method Detail

      • notifyElementPut

        public final void notifyElementPut​(Ehcache cache,
                                   Element element)
                            throws CacheException
        Called immediately after an element has been put into the cache. The Cache.put(net.sf.ehcache.Element) method will block until this method returns.

        Implementers may wish to have access to the Element's fields, including value, so the element is provided. Implementers should be careful not to modify the element. The effect of any modifications is undefined.

        This implementation queues the put notification for in-order replication to peers.

        Specified by:
        notifyElementPut in interface CacheEventListener
        Overrides:
        notifyElementPut in class RMISynchronousCacheReplicator
        Parameters:
        cache - the cache emitting the notification
        element - the element which was just put into the cache.
        Throws:
        CacheException

      • notifyElementUpdated

        public final void notifyElementUpdated​(Ehcache cache,
                                       Element element)
                                throws CacheException
        Called immediately after an element has been put into the cache and the element already existed in the cache. This is thus an update.

        The Cache.put(net.sf.ehcache.Element) method will block until this method returns.

        Implementers may wish to have access to the Element's fields, including value, so the element is provided. Implementers should be careful not to modify the element. The effect of any modifications is undefined.

        Specified by:
        notifyElementUpdated in interface CacheEventListener
        Overrides:
        notifyElementUpdated in class RMISynchronousCacheReplicator
        Parameters:
        cache - the cache emitting the notification
        element - the element which was just put into the cache.
        Throws:
        CacheException

      • notifyElementRemoved

        public final void notifyElementRemoved​(Ehcache cache,
                                       Element element)
                                throws CacheException
        Called immediately after an attempt to remove an element. The remove method will block until this method returns.

        This notification is received regardless of whether the cache had an element matching the removal key or not. If an element was removed, the element is passed to this method, otherwise a synthetic element, with only the key set is passed in.

        Specified by:
        notifyElementRemoved in interface CacheEventListener
        Overrides:
        notifyElementRemoved in class RMISynchronousCacheReplicator
        Parameters:
        cache - the cache emitting the notification
        element - the element just deleted, or a synthetic element with just the key set if no element was removed.
        Throws:
        CacheException

      • addToReplicationQueue

        protected void addToReplicationQueue​(RmiEventMessage eventMessage)
        Adds a message to the queue.

        This method checks the state of the replication thread and warns if it has stopped and then discards the message.

        Parameters:
        eventMessage -

      • clone

        public java.lang.Object clone()
                       throws java.lang.CloneNotSupportedException
        Creates a clone of this listener. This method will only be called by ehcache before a cache is initialized.

        This may not be possible for listeners after they have been initialized. Implementations should throw CloneNotSupportedException if they do not support clone.

        Specified by:
        clone in interface CacheEventListener
        Overrides:
        clone in class RMISynchronousCacheReplicator
        Returns:
        a clone
        Throws:
        java.lang.CloneNotSupportedException - if the listener could not be cloned.