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Ehcache is an open source, standards-based cache used to boost performance, offload the database and simplify scalability. Ehcache is robust, proven and full-featured and this has made it the most widely-used Java-based cache.

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/*
 * All content copyright Terracotta, Inc., unless otherwise indicated. All rights reserved.
 */
package org.terracotta.modules.ehcache.writebehind;

import net.sf.ehcache.CacheEntry;
import net.sf.ehcache.CacheException;
import net.sf.ehcache.Ehcache;
import net.sf.ehcache.Element;
import net.sf.ehcache.writer.CacheWriter;
import net.sf.ehcache.writer.writebehind.OperationsFilter;
import net.sf.ehcache.writer.writebehind.WriteBehind;

import org.terracotta.modules.ehcache.async.AsyncCoordinator;
import org.terracotta.modules.ehcache.async.scatterpolicies.ItemScatterPolicy;
import org.terracotta.modules.ehcache.writebehind.operations.DeleteAsyncOperation;
import org.terracotta.modules.ehcache.writebehind.operations.SingleAsyncOperation;
import org.terracotta.modules.ehcache.writebehind.operations.WriteAsyncOperation;

public class AsyncWriteBehind implements WriteBehind {
  public static final ItemScatterPolicy POLICY = new SingleAsyncOperationItemScatterPolicy();

  private final AsyncCoordinator async;
  private final int                                    concurrency;

  /**
   * Instantiate a new instance of {@code AsyncWriteBehind} by providing the async coordinator instance that will be
   * used for the underlying behavior.
   *
   * @param async the async coordinator instance that will be used by the write behind queue
   * @param writeBehindConcurrency the amount of buckets and threads to use
   */
  public AsyncWriteBehind(final AsyncCoordinator async, final int writeBehindConcurrency) {
    if(async == null) {
      throw new IllegalArgumentException("AsyncCoordinator can't be null");
    }
    if(writeBehindConcurrency < 1) {
      throw new IllegalArgumentException("writeBehindConcurrency has to be at least one");
    }
    this.async = async;
    this.concurrency = writeBehindConcurrency;
  }

  @Override
  public void start(CacheWriter writer) throws CacheException {
    async.start(new CacheWriterProcessor(writer), concurrency, POLICY);
  }

  // This method is to be called from within a clustered Lock as it does not take any clustered lock inside.
  @Override
  public void write(Element element) {
    async.add(new WriteAsyncOperation(element));
  }

  // This method is to be called from within a clustered Lock as it does not take any clustered lock inside.
  @Override
  public void delete(CacheEntry entry) {
    async.add(new DeleteAsyncOperation(entry.getKey(), entry.getElement()));
  }

  @Override
  public void setOperationsFilter(OperationsFilter filter) {
    OperationsFilterWrapper filterWrapper = new OperationsFilterWrapper(filter);
    async.setOperationsFilter(filterWrapper);
  }

  @Override
  public void stop() throws CacheException {
    async.stop();
  }

  @Override
  public long getQueueSize() {
    return async.getQueueSize();
  }

  private static class SingleAsyncOperationItemScatterPolicy implements ItemScatterPolicy {
    private SingleAsyncOperationItemScatterPolicy() {
      //
    }

    @Override
    public int selectBucket(final int count, final SingleAsyncOperation item) {
      Object key;
      try {
        key = item.getKey();
      } catch (Exception e) {
        throw new CacheException(e);
      }
      return Math.abs(key.hashCode() % count);
    }
  }

}