trunk/camel-core/src/main/java/org/apache/camel/component/file/GenericFileExclusiveReadLockStrategy.java

/**
 * 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.camel.component.file;

import org.apache.camel.Exchange;

/**
 * Strategy for acquiring exclusive read locks for files to be consumed. After
 * granting the read lock it is released, we just want to make sure that when
 * we start consuming the file its not currently in progress of being written by
 * third party.
 * <p/>
 * Camel supports out of the box the following strategies:
 * <ul>
 * <li>FileRenameExclusiveReadLockStrategy waiting until its possible to rename the file.</li>
 * <li>FileLockExclusiveReadLockStrategy acquiring a RW file lock for the duration of the processing.</li>
 * <li>MarkerFileExclusiveReadLockStrategy using a marker file for acquiring read lock.</li>
 * <li>FileChangedExclusiveReadLockStrategy using a file changed detection for acquiring read lock.</li>
 * </ul>
 */
public interface GenericFileExclusiveReadLockStrategy<T> {

    /**
     * Allows custom logic to be run on startup preparing the strategy, such as removing old lock files etc.
     *
     * @param operations generic file operations
     * @param endpoint   the endpoint
     * @throws Exception can be thrown in case of errors
     */
    void prepareOnStartup(GenericFileOperations<T> operations, GenericFileEndpoint<T> endpoint) throws Exception;

    /**
     * Acquires exclusive read lock to the file.
     *
     * @param operations generic file operations
     * @param file       the file
     * @param exchange   the exchange
     * @return <tt>true</tt> if read lock was acquired. If <tt>false</tt> Camel
     *         will skip the file and try it on the next poll
     * @throws Exception can be thrown in case of errors
     */
    boolean acquireExclusiveReadLock(GenericFileOperations<T> operations, GenericFile<T> file, Exchange exchange) throws Exception;

    /**
     * Releases the exclusive read lock granted by the <tt>acquireExclusiveReadLock</tt> method.
     *
     * @param operations generic file operations
     * @param file       the file
     * @param exchange   the exchange
     * @throws Exception can be thrown in case of errors
     */
    void releaseExclusiveReadLock(GenericFileOperations<T> operations, GenericFile<T> file, Exchange exchange) throws Exception;

    /**
     * Sets an optional timeout period.
     * <p/>
     * If the readlock could not be granted within the time period then the wait is stopped and the
     * <tt>acquireExclusiveReadLock</tt> method returns <tt>false</tt>.
     *
     * @param timeout period in millis
     */
    void setTimeout(long timeout);


    /**
     * Sets the check interval period.
     * <p/>
     * The check interval is used for sleeping between attempts to acquire read lock.
     * Setting a high value allows to cater for <i>slow writes</i> in case the producer
     * of the file is slow.
     * <p/>
     * The default period is 1000 millis.
     *
     * @param checkInterval interval in millis
     */
    void setCheckInterval(long checkInterval);

}