com.github.triceo.robozonky.app.Exclusivity Maven / Gradle / Ivy
/*
* Copyright 2017 Lukáš Petrovický
*
* 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.github.triceo.robozonky.app;
import java.io.File;
import java.io.IOException;
import java.io.RandomAccessFile;
import java.nio.channels.FileLock;
import java.util.Optional;
import java.util.function.Consumer;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
/**
* Used to ensure that only one RoboZonky process may be executing at any one time. See {@link #get()} for the
* contract. Will not mutually exclude RoboZonky instances running within the same JVM.
*/
final class Exclusivity implements ShutdownHook.Handler {
private static final Logger LOGGER = LoggerFactory.getLogger(Exclusivity.class);
private static final class LockControl {
private final RandomAccessFile randomAccessFile;
private final FileLock lock;
public LockControl(final File lockedFile) throws IOException {
this.randomAccessFile = new RandomAccessFile(lockedFile, "rw");
this.lock = this.randomAccessFile.getChannel().lock();
}
public boolean hasValidLock() {
return lock.isValid();
}
public void invalidateLock() throws IOException {
this.randomAccessFile.close();
}
}
private final File fileToLock;
private Exclusivity.LockControl lockControl = null;
/**
* Guarantees exclusivity based on a randomly created temp file. This is only useful for testing, since in all
* other cases multiple JVMs need to synchronize around the same file.
* @throws IOException When the temp file could not be created.
*/
Exclusivity() throws IOException {
this(File.createTempFile("robozonky-", ".lock"));
}
/**
* Guarantees exclusivity around a provided file.
* @param lock File to lock on.
*/
public Exclusivity(final File lock) {
this.fileToLock = lock;
}
File getFileToLock() {
return this.fileToLock;
}
/**
* Whether or not the application has managed to acquire exclusivity.
* @return True between any two successful successive calls to {@link #ensure()} and {@link #waive()} respectively.
* Will be false before first successful {@link #ensure()} or after every {@link #waive()}.
*/
synchronized boolean isEnsured() {
return lockControl != null && lockControl.hasValidLock();
}
/**
* Allow other instances of RoboZonky to run, possibly acquiring exclusivity for themselves.
*/
synchronized void waive() {
if (!this.isEnsured()) {
Exclusivity.LOGGER.debug("Already waived.");
return;
}
try {
this.lockControl.invalidateLock();
Exclusivity.LOGGER.debug("File lock released.");
} catch (final IOException ex) {
Exclusivity.LOGGER.warn("Failed releasing lock, new RoboZonky processes may not launch.", ex);
} finally {
Exclusivity.LOGGER.trace("Lock file deleted successfully: {}.", this.fileToLock.delete());
}
}
/**
* Will return after this instance of RoboZonky has acquired exclusivity, or failed. May block for extensive periods
* of time. Make sure to call {@link #isEnsured()} afterwards to see if exclusivity is ensured.
*/
synchronized void ensure() {
if (this.isEnsured()) {
Exclusivity.LOGGER.debug("Already ensured.");
return;
}
Exclusivity.LOGGER.debug("Acquiring file lock: {}.", this.fileToLock.getAbsolutePath());
try {
this.lockControl = new Exclusivity.LockControl(this.fileToLock);
Exclusivity.LOGGER.debug("File lock acquired.");
} catch (final IOException ex) {
Exclusivity.LOGGER.error("Failed acquiring lock, another RoboZonky process likely running.", ex);
}
}
/**
* Call in order to acquire exclusivity. May block for extensive periods of time until exclusivity is acquired.
* @return If present, call in order to waive exclusivity. If empty, exclusivity not acquired.
*/
@Override
public Optional> get() {
this.ensure();
if (!this.isEnsured()) {
return Optional.empty();
} else { // other RoboZonky instances can now start executing
return Optional.of((code) -> this.waive());
}
}
}