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.camel.util.StopWatch;
025 import org.slf4j.Logger;
026 import org.slf4j.LoggerFactory;
027
028 /**
029 * Acquires exclusive read lock to the given file. Will wait until the lock is granted.
030 * After granting the read lock it is released, we just want to make sure that when we start
031 * consuming the file its not currently in progress of being written by third party.
032 */
033 public class GenericFileRenameExclusiveReadLockStrategy<T> implements GenericFileExclusiveReadLockStrategy<T> {
034 private static final transient Logger LOG = LoggerFactory.getLogger(GenericFileRenameExclusiveReadLockStrategy.class);
035 private long timeout;
036 private long checkInterval;
037
038 public void prepareOnStartup(GenericFileOperations<T> operations, GenericFileEndpoint<T> endpoint) throws Exception {
039 // noop
040 }
041
042 public boolean acquireExclusiveReadLock(GenericFileOperations<T> operations, GenericFile<T> file,
043 Exchange exchange) throws Exception {
044 LOG.trace("Waiting for exclusive read lock to file: {}", file);
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 StopWatch watch = new StopWatch();
054
055 boolean exclusive = false;
056 while (!exclusive) {
057 // timeout check
058 if (timeout > 0) {
059 long delta = watch.taken();
060 if (delta > timeout) {
061 LOG.warn("Cannot acquire read lock within " + timeout + " millis. Will skip the file: " + file);
062 // we could not get the lock within the timeout period, so return false
063 return false;
064 }
065 }
066
067 exclusive = operations.renameFile(file.getAbsoluteFilePath(), newFile.getAbsoluteFilePath());
068 if (exclusive) {
069 LOG.trace("Acquired exclusive read lock to file: {}", file);
070 // rename it back so we can read it
071 operations.renameFile(newFile.getAbsoluteFilePath(), file.getAbsoluteFilePath());
072 } else {
073 boolean interrupted = sleep();
074 if (interrupted) {
075 // we were interrupted while sleeping, we are likely being shutdown so return false
076 return false;
077 }
078 }
079 }
080
081 return true;
082 }
083
084 public void releaseExclusiveReadLock(GenericFileOperations<T> operations, GenericFile<T> file,
085 Exchange exchange) throws Exception {
086 // noop
087 }
088
089 private boolean sleep() {
090 LOG.trace("Exclusive read lock not granted. Sleeping for {} millis.", checkInterval);
091 try {
092 Thread.sleep(checkInterval);
093 return false;
094 } catch (InterruptedException e) {
095 LOG.debug("Sleep interrupted while waiting for exclusive read lock, so breaking out");
096 return true;
097 }
098 }
099
100 public long getTimeout() {
101 return timeout;
102 }
103
104 public void setTimeout(long timeout) {
105 this.timeout = timeout;
106 }
107
108 public void setCheckInterval(long checkInterval) {
109 this.checkInterval = checkInterval;
110 }
111 }