net.sf.ehcache.distribution
Class RMIAsynchronousCacheReplicator
public final
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,
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: RMIAsynchronousCacheReplicator.java 141 2006-06-30 01:56:32Z gregluck $
Author: Greg Luck
Field Summary |
protected List | replicationQueue
A queue of updates. |
protected Thread | replicationThread
A thread which handles replication, so that replication can take place asynchronously and not hold up the cache |
protected static int | REPLICATION_THREAD_INTERVAL
The amount of time the replication thread sleeps after it detects the replicationQueue is empty
before checking again. |
protected final List replicationQueue
A queue of updates.
protected final Thread replicationThread
A thread which handles replication, so that replication can take place asynchronously and not hold up the cache
protected static final int REPLICATION_THREAD_INTERVAL
The amount of time the replication thread sleeps after it detects the replicationQueue is empty
before checking again.
protected RMIAsynchronousCacheReplicator(boolean replicatePuts, boolean replicateUpdates, boolean replicateUpdatesViaCopy, boolean replicateRemovals)
Constructor for internal and subclass use
Parameters: replicatePuts replicateUpdates replicateUpdatesViaCopy replicateRemovals
protected void addToReplicationQueue(RMIAsynchronousCacheReplicator.CacheEventMessage cacheEventMessage)
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: cacheEventMessage
public final void dispose()
Give the replicator a chance to cleanup and free resources when no longer needed
public final void notifyElementPut(
Cache cache,
Element element)
{@inheritDoc }
This implementation queues the put notification for in-order replication to peers.
Parameters: cache the cache emitting the notification element the element which was just put into the cache.
public final void notifyElementRemoved(
Cache cache,
Element element)
Called immediately after an element has been removed. The remove method will block until
this method returns.
This implementation queues the removal notification for in order replication to peers.
Parameters: cache the cache emitting the notification element just deleted
public final void notifyElementUpdated(
Cache cache,
Element element)
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
put 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.
Parameters: cache the cache emitting the notification element the element which was just put into the cache.