1/* 2 * Copyright (C) 2010 The Android Open Source Project 3 * 4 * Licensed under the Apache License, Version 2.0 (the "License"); 5 * you may not use this file except in compliance with the License. 6 * You may obtain a copy of the License at 7 * 8 * http://www.apache.org/licenses/LICENSE-2.0 9 * 10 * Unless required by applicable law or agreed to in writing, software 11 * distributed under the License is distributed on an "AS IS" BASIS, 12 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. 13 * See the License for the specific language governing permissions and 14 * limitations under the License. 15 */ 16 17package java.net; 18 19import java.security.AccessController; 20import java.util.LinkedHashMap; 21import java.util.Map; 22 23import org.apache.harmony.luni.util.PriviAction; 24 25/** 26 * Implements caching for {@code InetAddress}. We use a unified cache for both positive and negative 27 * cache entries. 28 */ 29class AddressCache { 30 /** 31 * When the cache contains more entries than this, we start dropping the oldest ones. 32 * This should be a power of two to avoid wasted space in our custom map. 33 */ 34 private static final int MAX_ENTRIES = 512; 35 36 // This isn't used by our HashMap implementation, but the API demands it. 37 private static final float DEFAULT_LOAD_FACTOR = .75F; 38 39 // Default time-to-live for positive cache entries. 600 seconds (10 minutes). 40 private static final long DEFAULT_POSITIVE_TTL_NANOS = 600 * 1000000000L; 41 // Default time-to-live for negative cache entries. 10 seconds. 42 private static final long DEFAULT_NEGATIVE_TTL_NANOS = 10 * 1000000000L; 43 44 // Failed lookups are represented in the cache my mappings to this empty array. 45 private static final InetAddress[] NO_ADDRESSES = new InetAddress[0]; 46 47 // The actual cache. 48 private final Map<String, AddressCacheEntry> map; 49 50 static class AddressCacheEntry { 51 // The addresses. May be the empty array for a negative cache entry. 52 InetAddress[] addresses; 53 54 /** 55 * The absolute expiry time in nanoseconds. Nanoseconds from System.nanoTime is ideal 56 * because -- unlike System.currentTimeMillis -- it can never go backwards. 57 * 58 * Unless we need to cope with DNS TTLs of 292 years, we don't need to worry about overflow. 59 */ 60 long expiryNanos; 61 62 AddressCacheEntry(InetAddress[] addresses, long expiryNanos) { 63 this.addresses = addresses; 64 this.expiryNanos = expiryNanos; 65 } 66 } 67 68 public AddressCache() { 69 // We pass 'true' so removeEldestEntry removes the least-recently accessed entry, rather 70 // than the least-recently inserted. 71 map = new LinkedHashMap<String, AddressCacheEntry>(0, DEFAULT_LOAD_FACTOR, true) { 72 @Override protected boolean removeEldestEntry(Entry<String, AddressCacheEntry> eldest) { 73 // By the time this method is called, the new entry has already been inserted and 74 // the map will have grown to accommodate it. Using == lets us prevent resizing. 75 return size() == MAX_ENTRIES; 76 } 77 }; 78 } 79 80 /** 81 * Returns the cached addresses associated with 'hostname'. Returns null if nothing is known 82 * about 'hostname'. Returns an empty array if 'hostname' is known not to exist. 83 */ 84 public InetAddress[] get(String hostname) { 85 AddressCacheEntry entry; 86 synchronized (map) { 87 entry = map.get(hostname); 88 } 89 // Do we have a valid cache entry? 90 if (entry != null && entry.expiryNanos >= System.nanoTime()) { 91 return entry.addresses; 92 } 93 // Either we didn't find anything, or it had expired. 94 // No need to remove expired entries: the caller will provide a replacement shortly. 95 return null; 96 } 97 98 /** 99 * Associates the given 'addresses' with 'hostname'. The association will expire after a 100 * certain length of time. 101 */ 102 public void put(String hostname, InetAddress[] addresses) { 103 // Calculate the expiry time. 104 boolean isPositive = (addresses.length > 0); 105 String propertyName = isPositive ? "networkaddress.cache.ttl" : "networkaddress.cache.negative.ttl"; 106 long defaultTtlNanos = isPositive ? DEFAULT_POSITIVE_TTL_NANOS : DEFAULT_NEGATIVE_TTL_NANOS; 107 // Fast-path the default case... 108 long expiryNanos = System.nanoTime() + defaultTtlNanos; 109 if (System.getSecurityManager() != null || System.getProperty(propertyName, null) != null) { 110 // ...and let those using a SecurityManager or custom properties pay full price. 111 expiryNanos = customTtl(propertyName, defaultTtlNanos); 112 if (expiryNanos == Long.MIN_VALUE) { 113 return; 114 } 115 } 116 // Update the cache. 117 synchronized (map) { 118 map.put(hostname, new AddressCacheEntry(addresses, expiryNanos)); 119 } 120 } 121 122 /** 123 * Records that 'hostname' is known not to have any associated addresses. (I.e. insert a 124 * negative cache entry.) 125 */ 126 public void putUnknownHost(String hostname) { 127 put(hostname, NO_ADDRESSES); 128 } 129 130 private long customTtl(String propertyName, long defaultTtlNanos) { 131 String ttlString = AccessController.doPrivileged(new PriviAction<String>(propertyName, null)); 132 if (ttlString == null) { 133 return System.nanoTime() + defaultTtlNanos; 134 } 135 try { 136 long ttlS = Long.parseLong(ttlString); 137 // For the system properties, -1 means "cache forever" and 0 means "don't cache". 138 if (ttlS == -1) { 139 return Long.MAX_VALUE; 140 } else if (ttlS == 0) { 141 return Long.MIN_VALUE; 142 } else { 143 return System.nanoTime() + ttlS * 1000000000L; 144 } 145 } catch (NumberFormatException ex) { 146 return System.nanoTime() + defaultTtlNanos; 147 } 148 } 149} 150