com.spotify.helios.testing.JobPrefixFile Maven / Gradle / Ivy
/*
* Copyright (c) 2014 Spotify AB.
*
* Licensed 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 com.spotify.helios.testing;
import com.google.common.base.Preconditions;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
import java.io.IOException;
import java.nio.channels.FileChannel;
import java.nio.channels.FileLock;
import java.nio.channels.OverlappingFileLockException;
import java.nio.file.Files;
import java.nio.file.Path;
import java.text.SimpleDateFormat;
import java.util.Date;
import java.util.concurrent.ThreadLocalRandom;
import static java.lang.Integer.toHexString;
import static java.nio.file.StandardOpenOption.CREATE_NEW;
import static java.nio.file.StandardOpenOption.WRITE;
/**
* This class is used to manage job prefix files on disk, which TemporaryJobs uses to keep track
* of old jobs which need to be cleaned up. The class allows you to create/delete files, and
* will handle all management of file locks and channels. When an instance of this class is no
* longer needed either {@link #release}, {@link #close} or {@link #delete} should be called so
* that the underlying FileChannel can be properly closed.
*/
class JobPrefixFile implements AutoCloseable {
private static final Logger log = LoggerFactory.getLogger(JobPrefixFile.class);
private final String prefix;
private final Path file;
private FileChannel channel;
private FileLock lock;
/**
* Creates a JobPrefixFile using a randomly generated filename in the specified directory.
* @return a new JobPrefixFile
* @throws IOException
*/
public static JobPrefixFile create(Path directory) throws IOException {
return create(null, directory);
}
/**
* Creates a JobPrefixFile using the specified prefix and directory.
* @param prefix the job prefix, which will be the name of the file
* @param directory the directory where the file will be created
* @return a new JobPrefixFile
* @throws IOException
*/
public static JobPrefixFile create(final String prefix, final Path directory)
throws IOException {
return new JobPrefixFile(prefix, directory);
}
/**
* Attempts to lock the given file, and create a JobPrefixFile for it. A new JobPrefixFile
* instance will be returned if a lock can be obtained for the file. Null will be returned if the
* lock is already held by either this process or another. For all other cases, an exception will
* be thrown.
* @param file the path to the file
* @return a new JobPrefixFile if a file lock can be obtained. Null if a lock for the file is
* already held by either this process or another.
*/
public static JobPrefixFile tryFromExistingFile(final Path file) throws IOException {
Preconditions.checkNotNull(file);
final FileChannel channel = FileChannel.open(file, WRITE);
final FileLock lock;
try {
// We want to return JobPrefixFile if we can obtain the lock, null if someone already holds
// the lock, and throw an exception in all other cases. tryLock makes this a little tricky.
// It's behavior this:
// - returns a FileLock if one can be obtained
// - returns null if another process holds the lock
// - throws OverlappingFileLockException if the lock is already held by this process
// - throws a various exceptions for other errors
lock = channel.tryLock();
} catch (OverlappingFileLockException e) {
// If the lock is already held by this process, close the channel and return null.
close(channel);
return null;
} catch (Exception e) {
// If an unexpected error occurred, close the channel and rethrow.
close(channel);
throw e;
}
// If another process hold the lock, close the channel and return null.
if (lock == null) {
close(channel);
return null;
}
// If we've obtained the lock, return a new JobPrefixFile
return new JobPrefixFile(file, channel, lock);
}
private JobPrefixFile(final String prefix, final Path directory) throws IOException {
Preconditions.checkNotNull(directory);
this.prefix = prefix == null
? "tmp-" + new SimpleDateFormat("yyyyMMdd").format(new Date()) + "-"
+ toHexString(ThreadLocalRandom.current().nextInt())
: prefix;
// Make sure directory exists, then create prefix file
Files.createDirectories(directory);
file = directory.resolve(this.prefix);
final Path tmp = directory.resolve(this.prefix + ".tmp");
try {
// If we didn't create the file with the .tmp extension, there would be a race condition
// where another process could read the file and try to delete it before we obtained the lock
this.channel = FileChannel.open(tmp, CREATE_NEW, WRITE);
this.lock = channel.lock();
Files.move(tmp, file);
} catch (Exception e) {
deleteIfExists(tmp);
deleteIfExists(file);
close(this.channel);
throw new RuntimeException("Failed to create job prefix file " + file, e);
}
}
private JobPrefixFile(final Path file, final FileChannel channel, final FileLock lock)
throws IOException, IllegalStateException {
this.file = Preconditions.checkNotNull(file, "file");
this.channel = Preconditions.checkNotNull(channel, "channel");
this.lock = Preconditions.checkNotNull(lock, "lock");
this.prefix = file.getFileName().toString();
}
/**
* Deletes the file, cleaning up any associated resources. This will not throw an exception.
* Either this method, {@link #release} or {@link #close} should be called when the instance is
* no longer needed.
*/
public void delete() {
release();
deleteIfExists(file);
}
/**
* Helper method to delete file if it exists. This will not thrown an exception.
* @param file the file to delete
*/
private void deleteIfExists(Path file) {
if (file != null) {
try {
// Use deleteIfExists because there is a slight chance another process deleted the file
// just after we deleted the lock.
Files.deleteIfExists(file);
} catch (Exception e) {
log.warn("Failed to delete file {}", file, e);
}
}
}
/**
* Return the job prefix which is the same as the file name.
* @return the job prefix
*/
public String prefix() {
return prefix;
}
/**
* Release the lock. If the lock has already been released, the method returns immediately. This
* method will not throw an exception. Either this method, {@link #close} or {@link #delete}
* should be called when the instance is no longer needed.
*/
public void release() {
close(lock);
lock = null;
close(channel);
channel = null;
}
/**
* Invokes {@link #release()}. Added so JobPrefixFile can be used within a try-with-resources
* statement. Either this method, {@link #release} or {@link #delete} should be called when the
* instance is no longer needed.
*/
@Override
public void close() {
release();
}
/**
* Helper method for closing any object which implements {@link java.lang.AutoCloseable}.
* Exceptions are swallowed, and nulls ignored.
* @param closeable the object to close
*/
private static void close(final AutoCloseable closeable) {
if (closeable != null) {
try {
closeable.close();
} catch (Exception e) {
log.debug("Failed to close {}", closeable.getClass().getSimpleName(), e);
}
}
}
}
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