/**
* Licensed to the Apache Software Foundation (ASF) under one
* or more contributor license agreements. See the NOTICE file
* distributed with this work for additional information
* regarding copyright ownership. The ASF licenses this file
* to you under the Apache License, Version 2.0 (the
* "License"); you may not use this file except in compliance
* with the License. You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
package org.apache.flume;
import org.apache.flume.channel.BasicChannelSemantics;
import org.apache.flume.channel.BasicTransactionSemantics;
/**
* <p>Provides the transaction boundary while accessing a channel.</p>
* <p>A <tt>Transaction</tt> instance is used to encompass channel access
* via the following idiom:</p>
* <pre><code>
* Channel ch = ...
* Transaction tx = ch.getTransaction();
* try {
* tx.begin();
* ...
* // ch.put(event) or ch.take()
* ...
* tx.commit();
* } catch (ChannelException ex) {
* tx.rollback();
* ...
* } finally {
* tx.close();
* }
* </code></pre>
* <p>Depending upon the implementation of the channel, the transaction
* semantics may be strong, or best-effort only.</p>
*
* <p>
* Transactions must be thread safe. To provide a guarantee of thread safe
* access to Transactions, see {@link BasicChannelSemantics} and
* {@link BasicTransactionSemantics}.
*
* @see org.apache.flume.Channel
*/
public interface Transaction {
public enum TransactionState {Started, Committed, RolledBack, Closed };
/**
* <p>Starts a transaction boundary for the current channel operation. If a
* transaction is already in progress, this method will join that transaction
* using reference counting.</p>
* <p><strong>Note</strong>: For every invocation of this method there must
* be a corresponding invocation of {@linkplain #close()} method. Failure
* to ensure this can lead to dangling transactions and unpredictable results.
* </p>
*/
public void begin();
/**
* Indicates that the transaction can be successfully committed. It is
* required that a transaction be in progress when this method is invoked.
*/
public void commit();
/**
* Indicates that the transaction can must be aborted. It is
* required that a transaction be in progress when this method is invoked.
*/
public void rollback();
/**
* <p>Ends a transaction boundary for the current channel operation. If a
* transaction is already in progress, this method will join that transaction
* using reference counting. The transaction is completed only if there
* are no more references left for this transaction.</p>
* <p><strong>Note</strong>: For every invocation of this method there must
* be a corresponding invocation of {@linkplain #begin()} method. Failure
* to ensure this can lead to dangling transactions and unpredictable results.
* </p>
*/
public void close();
}