001 /**
002 * Licensed to the Apache Software Foundation (ASF) under one or more
003 * contributor license agreements. See the NOTICE file distributed with
004 * this work for additional information regarding copyright ownership.
005 * The ASF licenses this file to You under the Apache License, Version 2.0
006 * (the "License"); you may not use this file except in compliance with
007 * the License. You may obtain a copy of the License at
008 *
009 * http://www.apache.org/licenses/LICENSE-2.0
010 *
011 * Unless required by applicable law or agreed to in writing, software
012 * distributed under the License is distributed on an "AS IS" BASIS,
013 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
014 * See the License for the specific language governing permissions and
015 * limitations under the License.
016 */
017 package org.apache.camel.component.file.strategy;
018
019 import org.apache.camel.Exchange;
020 import org.apache.camel.component.file.GenericFile;
021 import org.apache.camel.component.file.GenericFileEndpoint;
022 import org.apache.camel.component.file.GenericFileExclusiveReadLockStrategy;
023 import org.apache.camel.component.file.GenericFileOperations;
024 import org.apache.commons.logging.Log;
025 import org.apache.commons.logging.LogFactory;
026
027 /**
028 * Acquires exclusive read lock to the given file. Will wait until the lock is granted.
029 * After granting the read lock it is released, we just want to make sure that when we start
030 * consuming the file its not currently in progress of being written by third party.
031 */
032 public class GenericFileRenameExclusiveReadLockStrategy<T> implements GenericFileExclusiveReadLockStrategy<T> {
033 private static final transient Log LOG = LogFactory.getLog(GenericFileRenameExclusiveReadLockStrategy.class);
034 private long timeout;
035
036 public void prepareOnStartup(GenericFileOperations<T> operations, GenericFileEndpoint<T> endpoint) throws Exception {
037 // noop
038 }
039
040 public boolean acquireExclusiveReadLock(GenericFileOperations<T> operations, GenericFile<T> file,
041 Exchange exchange) throws Exception {
042 if (LOG.isTraceEnabled()) {
043 LOG.trace("Waiting for exclusive read lock to file: " + file);
044 }
045
046 // the trick is to try to rename the file, if we can rename then we have exclusive read
047 // since its a Generic file we cannot use java.nio to get a RW lock
048 String newName = file.getFileName() + ".camelExclusiveReadLock";
049
050 // make a copy as result and change its file name
051 GenericFile<T> newFile = file.copyFrom(file);
052 newFile.changeFileName(newName);
053
054 long start = System.currentTimeMillis();
055
056 boolean exclusive = false;
057 while (!exclusive) {
058 // timeout check
059 if (timeout > 0) {
060 long delta = System.currentTimeMillis() - start;
061 if (delta > timeout) {
062 LOG.warn("Cannot acquire read lock within " + timeout + " millis. Will skip the file: " + file);
063 // we could not get the lock within the timeout period, so return false
064 return false;
065 }
066 }
067
068 exclusive = operations.renameFile(file.getAbsoluteFilePath(), newFile.getAbsoluteFilePath());
069 if (exclusive) {
070 if (LOG.isTraceEnabled()) {
071 LOG.trace("Acquired exclusive read lock to file: " + file);
072 }
073 // rename it back so we can read it
074 operations.renameFile(newFile.getAbsoluteFilePath(), file.getAbsoluteFilePath());
075 } else {
076 boolean interrupted = sleep();
077 if (interrupted) {
078 // we were interrupted while sleeping, we are likely being shutdown so return false
079 return false;
080 }
081 }
082 }
083
084 return true;
085 }
086
087 public void releaseExclusiveReadLock(GenericFileOperations<T> operations, GenericFile<T> file,
088 Exchange exchange) throws Exception {
089 // noop
090 }
091
092 private boolean sleep() {
093 if (LOG.isTraceEnabled()) {
094 LOG.trace("Exclusive read lock not granted. Sleeping for 1000 millis.");
095 }
096 try {
097 Thread.sleep(1000);
098 return false;
099 } catch (InterruptedException e) {
100 LOG.debug("Sleep interrupted while waiting for exclusive read lock, so breaking out");
101 return true;
102 }
103 }
104
105 public long getTimeout() {
106 return timeout;
107 }
108
109 public void setTimeout(long timeout) {
110 this.timeout = timeout;
111 }
112 }