com.crankuptheamps.client.PublishStoreResizeHandler Maven / Gradle / Ivy
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package com.crankuptheamps.client;
/**
* Interface used to indicate whether a Store implementation is allowed to
* grow (or shrink) to the requested size. If the request to resize is
* denied, a Store implementation may fail the operation that resulted in
* the request to grow by throwing an exception.
*
*
* Implementation Example:
*
*
*
* public class MaxSizeResizeHandler implements PublishStoreResizeHandler, ConnectionStateListener {
* protected long maxSize; // Maximum allowed size for the publish store
* protected long timeout; // Timeout for store flushing
* protected int maxFlushAttempts; // Maximum number of attempts to flush the store
* protected volatile boolean connected = false; // Keeps track of the connection state
*
* public MaxSizeResizeHandler (long maxSize, long timeout, int maxFlushAttempts) {
* this.maxSize = maxSize;
* this.timeout = timeout;
* this.maxFlushAttempts = maxFlushAttempts;
* }
*
* @Overide
* public boolean invoke(Store store, long newSize) {
* try {
* if(newSize <= maxSize)
* return true;
*
* // Use your preferred logging API instead of println() calls.
* System.out.println("\n------- Resize Handler Called And Over Max Size --------");
*
* long startCount=store.unpersistedCount();
* System.out.println("Unpersisted count before flush: " + startCount);
*
* // We've reached max size. Try to flush store instead of growing it.
* long count=startCount;
* int tries=0;
* while(count > 0 && tries++ < maxFlushAttempts) {
* System.out.println("Store not empty. Unpersisted msg count = " + count);
* System.out.println("Flush attempt = " + tries + ", connected status = " + connected);
* try {
* store.flush(timeout);
* }
* catch(TimedOutException e) { /* ignore */ }
* count=store.unpersistedCount();
* }
* long endCount=store.unpersistedCount();
* System.out.println("Unpersisted count after flush attempt(s): " + endCount
* + ", connected = " + connected);
* } catch(Exception e) {
* e.printStackTrace();
* }
*
* // Let the store know it can't grow. Hopefully space was freed up.
* return false;
* }
*
* @Overide
* public void connectionStateChanged(int state) {
* switch(state) {
* case ConnectionStateListener.Connected:
* case ConnectionStateListener.LoggedOn:
* case ConnectionStateListener.HeartbeatInitiated:
* case ConnectionStateListener.PublishReplayed:
* case ConnectionStateListener.Resubscribed:
* connected = true;
* break;
* case ConnectionStateListener.Disconnected:
* case ConnectionStateListener.Shutdown:
* connected = false;
* break;
* }
* }
* }
*
*
*
* How to use your resize handler:
*
*
*
* client = new HAClient("PubClient");
* Store pubStore = new MemoryPublishStore(100);
* MaxSizeResizeHandler handler = new MaxSizeResizeHandler(maxSize, timeout, maxFlushAttempts);
* pubStore.setResizeHandler(handler);
* client.setPublishStore(pubStore);
* client.addConnectionStateListener(handler);
*
*
*
* You can implement your custom resize handler by implementing the
* {@link PublishStoreResizeHandler} interface and then setting it using the
* {@link PublishStore#setResizeHandler(PublishStoreResizeHandler)} method.
*
*/
public interface PublishStoreResizeHandler
{
/**
* Called by the {@link Store} when it wants to attempt a resize. Rather
* than allow a resize request to grow the store, and implementation
* could choose to flush the store (to allow space to be freed up)
* at the expense of publishing performance. If the store's unpersisted
* count doesn't decrease after a flush times out, it could indicate
* the client is disconnected or a server-side issue such as a
* synchronous replication destination is down.
*
* @param store The store sending the resize request.
* @param size The new size the store would like to resize to.
* @return A boolean indicating whether the Store is allowed to resize or not.
*/
public boolean invoke(Store store, long size);
}