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/*
* Copyright (c) 2014 Spotify AB.
*
* 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 com.spotify.helios.servicescommon;
import com.google.common.base.Objects;
import com.google.common.base.Supplier;
import com.google.common.base.Throwables;
import com.fasterxml.jackson.core.type.TypeReference;
import com.fasterxml.jackson.databind.JavaType;
import com.spotify.helios.common.Json;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
import java.io.IOException;
import java.io.InterruptedIOException;
import java.nio.channels.ClosedByInterruptException;
import java.nio.file.FileSystems;
import java.nio.file.Files;
import java.nio.file.Path;
import static com.google.common.base.Charsets.UTF_8;
import static java.nio.file.StandardCopyOption.ATOMIC_MOVE;
import static java.nio.file.StandardCopyOption.REPLACE_EXISTING;
/**
* A class that is similar to {@code AtomicReference} but is backed by a file, so can be
* persisted across a server restart. Assumes the underlying type can be serialized by Jackson.
*
* Strangely, this is not actually atomic in the {@code AtomicReference} way; i.e. not threadsafe,
* nor does it do CAS.
*/
public class PersistentAtomicReference {
private static final Logger log = LoggerFactory.getLogger(PersistentAtomicReference.class);
private final Path filename;
private final Path tempfilename;
private final Object sync = new Object();
private volatile T value;
private PersistentAtomicReference(final Path filename,
final JavaType javaType,
final Supplier initialValue)
throws IOException, InterruptedException {
try {
this.filename = filename.toAbsolutePath();
this.tempfilename = filename.getFileSystem().getPath(this.filename.toString() + ".tmp");
if (Files.exists(filename)) {
final byte[] bytes = Files.readAllBytes(filename);
if (bytes.length > 0) {
value = Json.read(bytes, javaType);
} else {
value = initialValue.get();
}
} else {
value = initialValue.get();
}
} catch (InterruptedIOException | ClosedByInterruptException e) {
throw new InterruptedException(e.getMessage());
}
}
/**
* Set the reference to {@code newValue}.
*
* @param newValue The value to set.
* @throws IOException If an error occurs working with the file on disk.
* @throws InterruptedException If the thread is interrupted.
*/
public void set(T newValue) throws IOException, InterruptedException {
try {
set0(newValue);
} catch (InterruptedIOException | ClosedByInterruptException e) {
throw new InterruptedException(e.getMessage());
}
}
private void set0(final T newValue) throws IOException {
log.debug("set: ({}) {}", filename, newValue);
synchronized (sync) {
final String json = Json.asPrettyStringUnchecked(newValue);
log.debug("write: ({}) {}", tempfilename, json);
Files.write(tempfilename, json.getBytes(UTF_8));
log.debug("move: {} -> {}", tempfilename, filename);
Files.move(tempfilename, filename, ATOMIC_MOVE, REPLACE_EXISTING);
this.value = newValue;
}
}
/**
* Set the reference to {@code newValue}, and wraps {@link IOException}s in
* {@link RuntimeException}s.
*
* @param newValue The value to set.
* @throws InterruptedException If the thread is interrupted.
*/
public void setUnchecked(T newValue) throws InterruptedException {
try {
set(newValue);
} catch (IOException e) {
throw Throwables.propagate(e);
}
}
/**
* Returns the value stored.
*
* @return The value.
*/
public T get() {
return value;
}
public static PersistentAtomicReference create(final Path filename,
final TypeReference typeReference,
final Supplier initialValue)
throws IOException, InterruptedException {
return new PersistentAtomicReference<>(filename, Json.type(typeReference), initialValue);
}
public static PersistentAtomicReference create(final String filename,
final TypeReference typeReference,
final Supplier initialValue)
throws IOException, InterruptedException {
return create(FileSystems.getDefault().getPath(filename), typeReference, initialValue);
}
public static PersistentAtomicReference create(final Path filename,
final JavaType javaType,
final Supplier initialValue)
throws IOException, InterruptedException {
return new PersistentAtomicReference<>(filename, javaType, initialValue);
}
public static PersistentAtomicReference create(final String filename,
final JavaType javaType,
final Supplier initialValue)
throws IOException, InterruptedException {
return create(FileSystems.getDefault().getPath(filename), javaType, initialValue);
}
@Override
public String toString() {
return Objects.toStringHelper(this)
.add("filename", filename)
.toString();
}
}
