| // Copyright (C) 2017 The Android Open Source Project |
| // |
| // 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.googlesource.gerrit.plugins.events.fsstore; |
| |
| import java.io.IOException; |
| import java.nio.file.Files; |
| import java.nio.file.Path; |
| |
| /** Helper file for serialzing and storing a single type in a file */ |
| public class FileValue<T> { |
| protected final Path path; |
| protected Serializer<T> serializer; |
| |
| /** |
| * Use this constructor to use a builtin serializer (String or Long), and be sure to call init(T) |
| * with a value of your type for the serializer auto identification to happen. |
| */ |
| public FileValue(Path path) { |
| this(path, (Serializer<T>) null); |
| } |
| |
| public FileValue(Path path, Serializer<T> serializer) { |
| this.path = path; |
| this.serializer = serializer; |
| } |
| |
| /** Should be called by subclasses when initializing their file to a value. */ |
| protected void init(T init) { |
| initSerializer(init); |
| } |
| |
| /** |
| * Auto setup the serializer based on the type used to initialize the class. |
| * |
| * <p>Must be called with a supported type before use if a serializer has been set manualy. Safe |
| * to call if the Serializer was already set. |
| */ |
| protected void initSerializer(T init) { |
| if (serializer == null) { |
| if (init instanceof String) { |
| serializer = (Serializer<T>) new Serializer.String(); |
| } else if (init instanceof Long) { |
| serializer = (Serializer<T>) new Serializer.Long(); |
| } |
| } |
| } |
| |
| /** get (read) the unserialized object from the file with retries for stale file handles (NFS). */ |
| public T spinGet(long maxTries) throws IOException { |
| for (long i = 0; i < maxTries; i++) { |
| try { |
| return get(); |
| } catch (IOException e) { |
| Nfs.throwIfNotStaleFileHandle(e); |
| } |
| } |
| throw new IOException( |
| "Cannot read file " + path + " after " + maxTries + " Stale file handle tries."); |
| } |
| |
| /** get (read) the unserialized object from the file */ |
| protected T get() throws IOException { |
| return serializer.fromString(read()); |
| } |
| |
| /** The lowest level raw String read of the file */ |
| protected String read() throws IOException { |
| return Fs.readFile(path); |
| } |
| |
| /** Serialize object to given tmp file in preparation to call update() */ |
| protected void prepareT(Path tmp, T t) throws IOException { |
| prepare(tmp, serializer.fromGeneric(t)); |
| } |
| |
| /** Atmoically update (replace) file with src file. */ |
| protected boolean update(Path src) throws IOException { |
| return Fs.tryAtomicMove(src, path); |
| } |
| |
| /** Low level raw string write to given tmp file in preparation to call update(). */ |
| protected static void prepare(Path tmp, String s) throws IOException { |
| Files.write(tmp, s.getBytes()); |
| } |
| } |