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 17 package java.net; 18 19 import libcore.util.BasicLruCache; 20 21 /** 22 * Implements caching for {@code InetAddress}. We use a unified cache for both positive and negative 23 * cache entries. 24 * 25 * TODO: benchmark and optimize InetAddress until we get to the point where we can just rely on 26 * the C library level caching. The main thing caching at this level buys us is avoiding repeated 27 * conversions from 'struct sockaddr's to InetAddress[]. 28 */ 29 class 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 = 16; 35 36 // The TTL for the Java-level cache is short, just 2s. 37 private static final long TTL_NANOS = 2 * 1000000000L; 38 39 // The actual cache. 40 private final BasicLruCache<String, AddressCacheEntry> cache 41 = new BasicLruCache<String, AddressCacheEntry>(MAX_ENTRIES); 42 43 static class AddressCacheEntry { 44 // Either an InetAddress[] for a positive entry, 45 // or a String detail message for a negative entry. 46 final Object value; 47 48 /** 49 * The absolute expiry time in nanoseconds. Nanoseconds from System.nanoTime is ideal 50 * because -- unlike System.currentTimeMillis -- it can never go backwards. 51 * 52 * We don't need to worry about overflow with a TTL_NANOS of 2s. 53 */ 54 final long expiryNanos; 55 AddressCacheEntry(Object value)56 AddressCacheEntry(Object value) { 57 this.value = value; 58 this.expiryNanos = System.nanoTime() + TTL_NANOS; 59 } 60 } 61 62 /** 63 * Removes all entries from the cache. 64 */ clear()65 public void clear() { 66 cache.evictAll(); 67 } 68 69 /** 70 * Returns the cached InetAddress[] associated with 'hostname'. Returns null if nothing is known 71 * about 'hostname'. Returns a String suitable for use as an UnknownHostException detail 72 * message if 'hostname' is known not to exist. 73 */ get(String hostname)74 public Object get(String hostname) { 75 AddressCacheEntry entry = cache.get(hostname); 76 // Do we have a valid cache entry? 77 if (entry != null && entry.expiryNanos >= System.nanoTime()) { 78 return entry.value; 79 } 80 // Either we didn't find anything, or it had expired. 81 // No need to remove expired entries: the caller will provide a replacement shortly. 82 return null; 83 } 84 85 /** 86 * Associates the given 'addresses' with 'hostname'. The association will expire after a 87 * certain length of time. 88 */ put(String hostname, InetAddress[] addresses)89 public void put(String hostname, InetAddress[] addresses) { 90 cache.put(hostname, new AddressCacheEntry(addresses)); 91 } 92 93 /** 94 * Records that 'hostname' is known not to have any associated addresses. (I.e. insert a 95 * negative cache entry.) 96 */ putUnknownHost(String hostname, String detailMessage)97 public void putUnknownHost(String hostname, String detailMessage) { 98 cache.put(hostname, new AddressCacheEntry(detailMessage)); 99 } 100 } 101