001/* 002 * (C) Copyright 2017 Nuxeo (http://nuxeo.com/) and others. 003 * 004 * Licensed under the Apache License, Version 2.0 (the "License"); 005 * you may not use this file except in compliance with the License. 006 * You may obtain a copy of the License at 007 * 008 * http://www.apache.org/licenses/LICENSE-2.0 009 * 010 * Unless required by applicable law or agreed to in writing, software 011 * distributed under the License is distributed on an "AS IS" BASIS, 012 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. 013 * See the License for the specific language governing permissions and 014 * limitations under the License. 015 * 016 * Contributors: 017 * Florent Guillaume 018 */ 019package org.nuxeo.ecm.core.storage.kv; 020 021import java.util.Arrays; 022import java.util.HashMap; 023import java.util.Map; 024import java.util.Objects; 025import java.util.concurrent.locks.Lock; 026import java.util.concurrent.locks.ReadWriteLock; 027import java.util.concurrent.locks.ReentrantReadWriteLock; 028 029/** 030 * Memory-based implementation of a Key/Value store. 031 * 032 * @since 9.1 033 */ 034public class MemKeyValueStore implements KeyValueStoreProvider { 035 036 protected final Map<String, byte[]> map; 037 038 protected final Lock readLock; 039 040 protected final Lock writeLock; 041 042 public MemKeyValueStore() { 043 ReadWriteLock rwLock = new ReentrantReadWriteLock(); 044 readLock = rwLock.readLock(); 045 writeLock = rwLock.writeLock(); 046 // We can't use ConcurrentHashMap because compareAndSet needs to compare by value 047 // and ConcurrentHashMap doesn't know how to do that. Instead we use full locking; 048 // this is ok as this class isn't expected to be used in a high write rate scenario. 049 map = new HashMap<>(); 050 } 051 052 @Override 053 public void initialize(Map<String, String> properties) { 054 } 055 056 @Override 057 public void close() { 058 } 059 060 @Override 061 public void clear() { 062 writeLock.lock(); 063 try { 064 map.clear(); 065 } finally { 066 writeLock.unlock(); 067 } 068 } 069 070 protected static byte[] clone(byte[] value) { 071 return value == null ? null : value.clone(); 072 } 073 074 @Override 075 public void put(String key, byte[] value) { 076 Objects.requireNonNull(key); 077 value = clone(value); 078 writeLock.lock(); 079 try { 080 map.put(key, value); 081 } finally { 082 writeLock.unlock(); 083 } 084 } 085 086 @Override 087 public byte[] get(String key) { 088 Objects.requireNonNull(key); 089 byte[] value; 090 readLock.lock(); 091 try { 092 value = map.get(key); 093 } finally { 094 readLock.unlock(); 095 } 096 return clone(value); 097 } 098 099 @Override 100 public boolean compareAndSet(String key, byte[] expected, byte[] value) { 101 Objects.requireNonNull(key); 102 // clone is not needed if the comparison fails 103 // but we are optimistic and prefer to do the clone outside the lock 104 value = clone(value); 105 writeLock.lock(); 106 try { 107 byte[] current = map.get(key); 108 boolean equal = Arrays.equals(expected, current); 109 if (equal) { 110 map.put(key, value); 111 } 112 return equal; 113 } finally { 114 writeLock.unlock(); 115 } 116 } 117 118}