| /* |
| * 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 java.security.AccessController; |
| import java.util.LinkedHashMap; |
| import java.util.Map; |
| import org.apache.harmony.luni.util.PriviAction; |
| |
| /** |
| * Implements caching for {@code InetAddress}. We use a unified cache for both positive and negative |
| * cache entries. |
| */ |
| 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 = 512; |
| |
| // This isn't used by our HashMap implementation, but the API demands it. |
| private static final float DEFAULT_LOAD_FACTOR = .75F; |
| |
| // Default time-to-live for positive cache entries. 600 seconds (10 minutes). |
| private static final long DEFAULT_POSITIVE_TTL_NANOS = 600 * 1000000000L; |
| // Default time-to-live for negative cache entries. 10 seconds. |
| private static final long DEFAULT_NEGATIVE_TTL_NANOS = 10 * 1000000000L; |
| |
| // Failed lookups are represented in the cache my mappings to this empty array. |
| private static final InetAddress[] NO_ADDRESSES = new InetAddress[0]; |
| |
| // The actual cache. |
| private final Map<String, AddressCacheEntry> map; |
| |
| static class AddressCacheEntry { |
| // The addresses. May be the empty array for a negative cache entry. |
| InetAddress[] addresses; |
| |
| /** |
| * The absolute expiry time in nanoseconds. Nanoseconds from System.nanoTime is ideal |
| * because -- unlike System.currentTimeMillis -- it can never go backwards. |
| * |
| * Unless we need to cope with DNS TTLs of 292 years, we don't need to worry about overflow. |
| */ |
| long expiryNanos; |
| |
| AddressCacheEntry(InetAddress[] addresses, long expiryNanos) { |
| this.addresses = addresses; |
| this.expiryNanos = expiryNanos; |
| } |
| } |
| |
| public AddressCache() { |
| // We pass 'true' so removeEldestEntry removes the least-recently accessed entry, rather |
| // than the least-recently inserted. |
| map = new LinkedHashMap<String, AddressCacheEntry>(0, DEFAULT_LOAD_FACTOR, true) { |
| @Override protected boolean removeEldestEntry(Entry<String, AddressCacheEntry> eldest) { |
| // By the time this method is called, the new entry has already been inserted and |
| // the map will have grown to accommodate it. Using == lets us prevent resizing. |
| return size() == MAX_ENTRIES; |
| } |
| }; |
| } |
| |
| /** |
| * Returns the cached addresses associated with 'hostname'. Returns null if nothing is known |
| * about 'hostname'. Returns an empty array if 'hostname' is known not to exist. |
| */ |
| public InetAddress[] get(String hostname) { |
| AddressCacheEntry entry; |
| synchronized (map) { |
| entry = map.get(hostname); |
| } |
| // Do we have a valid cache entry? |
| if (entry != null && entry.expiryNanos >= System.nanoTime()) { |
| return entry.addresses; |
| } |
| // 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) { |
| // Calculate the expiry time. |
| boolean isPositive = (addresses.length > 0); |
| String propertyName = isPositive ? "networkaddress.cache.ttl" : "networkaddress.cache.negative.ttl"; |
| long defaultTtlNanos = isPositive ? DEFAULT_POSITIVE_TTL_NANOS : DEFAULT_NEGATIVE_TTL_NANOS; |
| // Fast-path the default case... |
| long expiryNanos = System.nanoTime() + defaultTtlNanos; |
| if (System.getSecurityManager() != null || System.getProperty(propertyName, null) != null) { |
| // ...and let those using a SecurityManager or custom properties pay full price. |
| expiryNanos = customTtl(propertyName, defaultTtlNanos); |
| if (expiryNanos == Long.MIN_VALUE) { |
| return; |
| } |
| } |
| // Update the cache. |
| synchronized (map) { |
| map.put(hostname, new AddressCacheEntry(addresses, expiryNanos)); |
| } |
| } |
| |
| /** |
| * Records that 'hostname' is known not to have any associated addresses. (I.e. insert a |
| * negative cache entry.) |
| */ |
| public void putUnknownHost(String hostname) { |
| put(hostname, NO_ADDRESSES); |
| } |
| |
| private long customTtl(String propertyName, long defaultTtlNanos) { |
| String ttlString = AccessController.doPrivileged(new PriviAction<String>(propertyName, null)); |
| if (ttlString == null) { |
| return System.nanoTime() + defaultTtlNanos; |
| } |
| try { |
| long ttlS = Long.parseLong(ttlString); |
| // For the system properties, -1 means "cache forever" and 0 means "don't cache". |
| if (ttlS == -1) { |
| return Long.MAX_VALUE; |
| } else if (ttlS == 0) { |
| return Long.MIN_VALUE; |
| } else { |
| return System.nanoTime() + ttlS * 1000000000L; |
| } |
| } catch (NumberFormatException ex) { |
| return System.nanoTime() + defaultTtlNanos; |
| } |
| } |
| } |