| /* |
| * Copyright (C) 2010 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 java.net; |
| |
| import libcore.util.BasicLruCache; |
| |
| /** |
| * Implements caching for {@code InetAddress}. We use a unified cache for both positive and negative |
| * cache entries. |
| * |
| * TODO: benchmark and optimize InetAddress until we get to the point where we can just rely on |
| * the C library level caching. The main thing caching at this level buys us is avoiding repeated |
| * conversions from 'struct sockaddr's to InetAddress[]. |
| */ |
| class AddressCache { |
| /** |
| * When the cache contains more entries than this, we start dropping the oldest ones. |
| * This should be a power of two to avoid wasted space in our custom map. |
| */ |
| private static final int MAX_ENTRIES = 16; |
| |
| // The TTL for the Java-level cache is short, just 2s. |
| private static final long TTL_NANOS = 2 * 1000000000L; |
| |
| // The actual cache. |
| private final BasicLruCache<String, AddressCacheEntry> cache |
| = new BasicLruCache<String, AddressCacheEntry>(MAX_ENTRIES); |
| |
| static class AddressCacheEntry { |
| // Either an InetAddress[] for a positive entry, |
| // or a String detail message for a negative entry. |
| final Object value; |
| |
| /** |
| * The absolute expiry time in nanoseconds. Nanoseconds from System.nanoTime is ideal |
| * because -- unlike System.currentTimeMillis -- it can never go backwards. |
| * |
| * We don't need to worry about overflow with a TTL_NANOS of 2s. |
| */ |
| final long expiryNanos; |
| |
| AddressCacheEntry(Object value) { |
| this.value = value; |
| this.expiryNanos = System.nanoTime() + TTL_NANOS; |
| } |
| } |
| |
| /** |
| * Removes all entries from the cache. |
| */ |
| public void clear() { |
| cache.evictAll(); |
| } |
| |
| /** |
| * Returns the cached InetAddress[] associated with 'hostname'. Returns null if nothing is known |
| * about 'hostname'. Returns a String suitable for use as an UnknownHostException detail |
| * message if 'hostname' is known not to exist. |
| */ |
| public Object get(String hostname) { |
| AddressCacheEntry entry = cache.get(hostname); |
| // Do we have a valid cache entry? |
| if (entry != null && entry.expiryNanos >= System.nanoTime()) { |
| return entry.value; |
| } |
| // Either we didn't find anything, or it had expired. |
| // No need to remove expired entries: the caller will provide a replacement shortly. |
| return null; |
| } |
| |
| /** |
| * Associates the given 'addresses' with 'hostname'. The association will expire after a |
| * certain length of time. |
| */ |
| public void put(String hostname, InetAddress[] addresses) { |
| cache.put(hostname, new AddressCacheEntry(addresses)); |
| } |
| |
| /** |
| * Records that 'hostname' is known not to have any associated addresses. (I.e. insert a |
| * negative cache entry.) |
| */ |
| public void putUnknownHost(String hostname, String detailMessage) { |
| cache.put(hostname, new AddressCacheEntry(detailMessage)); |
| } |
| } |