{"action":"created","comment":{"url":"https://api.github.com/repos/elastic/elasticsearch/pulls/comments/41400146","id":41400146,"diff_hunk":"@@ -0,0 +1,665 @@\n+/*\n+ * Licensed to Elasticsearch under one or more contributor\n+ * license agreements. See the NOTICE file distributed with\n+ * this work for additional information regarding copyright\n+ * ownership. Elasticsearch licenses this file to you under\n+ * the Apache License, Version 2.0 (the \"License\"); you may\n+ * not use this file except in compliance with the License.\n+ * You may obtain a copy of the License at\n+ *\n+ *    http://www.apache.org/licenses/LICENSE-2.0\n+ *\n+ * Unless required by applicable law or agreed to in writing,\n+ * software distributed under the License is distributed on an\n+ * \"AS IS\" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY\n+ * KIND, either express or implied.  See the License for the\n+ * specific language governing permissions and limitations\n+ * under the License.\n+ */\n+\n+package org.elasticsearch.common.cache;\n+\n+import org.elasticsearch.common.collect.Tuple;\n+import org.elasticsearch.common.util.concurrent.ReleasableLock;\n+\n+import java.util.*;\n+import java.util.concurrent.ExecutionException;\n+import java.util.concurrent.atomic.LongAdder;\n+import java.util.concurrent.locks.ReadWriteLock;\n+import java.util.concurrent.locks.ReentrantLock;\n+import java.util.concurrent.locks.ReentrantReadWriteLock;\n+import java.util.function.Function;\n+import java.util.function.ToLongBiFunction;\n+\n+/**\n+ * A simple concurrent cache.\n+ * <p>\n+ * Cache is a simple concurrent cache that supports time-based and weight-based evictions, with notifications for all\n+ * evictions. The design goals for this cache were simplicity and read performance. This means that we are willing to\n+ * accept reduced write performance in exchange for easy-to-understand code. Cache statistics for hits, misses and\n+ * evictions are exposed.\n+ * <p>\n+ * The design of the cache is relatively simple. The cache is segmented into 256 segments which are backed by HashMaps.\n+ * The segments are protected by a re-entrant read/write lock. The read/write locks permit multiple concurrent readers\n+ * without contention, and the segments gives us write throughput without impacting readers (so readers are blocked only\n+ * if they are reading a segment that a writer is writing to).\n+ * <p>\n+ * The LRU functionality is backed by a single doubly-linked list chaining the entries in order of insertion. This\n+ * LRU list is protected by a lock that serializes all writes to it. There are opportunities for improvements\n+ * here if write throughput is a concern.\n+ * <ol>\n+ * <li>LRU list mutations could be inserted into a blocking queue that a single thread is reading from\n+ * and applying to the LRU list.</li>\n+ * <li>Promotions could be deferred for entries that were \"recently\" promoted.</li>\n+ * <li>Locks on the list could be taken per node being modified instead of globally.</li>\n+ * </ol>\n+ * <p>\n+ * Evictions only occur after a mutation to the cache (meaning an entry promotion, a cache insertion, or a manual\n+ * invalidation) or an explicit call to {@link #refresh()}.\n+ *\n+ * @param <K> The type of the keys\n+ * @param <V> The type of the values\n+ */\n+public class Cache<K, V> {\n+    // positive if entries have an expiration\n+    private long expireAfterAccess = -1;\n+\n+    // true if entries can expire after access\n+    private boolean entriesExpireAfterAccess;","path":"core/src/main/java/org/elasticsearch/common/cache/Cache.java","position":67,"original_position":68,"commit_id":"37becf3dc2a1886fe5032536ec9ce766d93c78d8","original_commit_id":"bde4889daf8c07b2b55bd2a937fad47e8cadac04","user":{"login":"nik9000","id":215970,"avatar_url":"https://avatars.githubusercontent.com/u/215970?v=3","gravatar_id":"","url":"https://api.github.com/users/nik9000","html_url":"https://github.com/nik9000","followers_url":"https://api.github.com/users/nik9000/followers","following_url":"https://api.github.com/users/nik9000/following{/other_user}","gists_url":"https://api.github.com/users/nik9000/gists{/gist_id}","starred_url":"https://api.github.com/users/nik9000/starred{/owner}{/repo}","subscriptions_url":"https://api.github.com/users/nik9000/subscriptions","organizations_url":"https://api.github.com/users/nik9000/orgs","repos_url":"https://api.github.com/users/nik9000/repos","events_url":"https://api.github.com/users/nik9000/events{/privacy}","received_events_url":"https://api.github.com/users/nik9000/received_events","type":"User","site_admin":false},"body":"I don't think it changed the readability much - it made the checks simpler but then it left me wondering why two variables were needed. I was doing the \"why does this have to be here, let me think hard about it\" think.","created_at":"2015-10-07T14:54:53Z","updated_at":"2015-10-07T14:54:53Z","html_url":"https://github.com/elastic/elasticsearch/pull/13879#discussion_r41400146","pull_request_url":"https://api.github.com/repos/elastic/elasticsearch/pulls/13879","_links":{"self":{"href":"https://api.github.com/repos/elastic/elasticsearch/pulls/comments/41400146"},"html":{"href":"https://github.com/elastic/elasticsearch/pull/13879#discussion_r41400146"},"pull_request":{"href":"https://api.github.com/repos/elastic/elasticsearch/pulls/13879"}}},"pull_request":{"url":"https://api.github.com/repos/elastic/elasticsearch/pulls/13879","id":46450431,"html_url":"https://github.com/elastic/elasticsearch/pull/13879","diff_url":"https://github.com/elastic/elasticsearch/pull/13879.diff","patch_url":"https://github.com/elastic/elasticsearch/pull/13879.patch","issue_url":"https://api.github.com/repos/elastic/elasticsearch/issues/13879","number":13879,"state":"open","locked":false,"title":"Replace Guava cache with simple concurrent LRU cache","user":{"login":"jasontedor","id":4744941,"avatar_url":"https://avatars.githubusercontent.com/u/4744941?v=3","gravatar_id":"","url":"https://api.github.com/users/jasontedor","html_url":"https://github.com/jasontedor","followers_url":"https://api.github.com/users/jasontedor/followers","following_url":"https://api.github.com/users/jasontedor/following{/other_user}","gists_url":"https://api.github.com/users/jasontedor/gists{/gist_id}","starred_url":"https://api.github.com/users/jasontedor/starred{/owner}{/repo}","subscriptions_url":"https://api.github.com/users/jasontedor/subscriptions","organizations_url":"https://api.github.com/users/jasontedor/orgs","repos_url":"https://api.github.com/users/jasontedor/repos","events_url":"https://api.github.com/users/jasontedor/events{/privacy}","received_events_url":"https://api.github.com/users/jasontedor/received_events","type":"User","site_admin":false},"body":"This pull request replaces the Guava cache with a simple concurrent LRU cache with flexible eviction policies.\r\n","created_at":"2015-09-30T20:14:14Z","updated_at":"2015-10-07T14:54:53Z","closed_at":null,"merged_at":null,"merge_commit_sha":"decfaa80cf63b8d8bc6179247b35c400a4bdb10e","assignee":null,"milestone":null,"commits_url":"https://api.github.com/repos/elastic/elasticsearch/pulls/13879/commits","review_comments_url":"https://api.github.com/repos/elastic/elasticsearch/pulls/13879/comments","review_comment_url":"https://api.github.com/repos/elastic/elasticsearch/pulls/comments{/number}","comments_url":"https://api.github.com/repos/elastic/elasticsearch/issues/13879/comments","statuses_url":"https://api.github.com/repos/elastic/elasticsearch/statuses/37becf3dc2a1886fe5032536ec9ce766d93c78d8","head":{"label":"jasontedor:straight-cache-homey","ref":"straight-cache-homey","sha":"37becf3dc2a1886fe5032536ec9ce766d93c78d8","user":{"login":"jasontedor","id":4744941,"avatar_url":"https://avatars.githubusercontent.com/u/4744941?v=3","gravatar_id":"","url":"https://api.github.com/users/jasontedor","html_url":"https://github.com/jasontedor","followers_url":"https://api.github.com/users/jasontedor/followers","following_url":"https://api.github.com/users/jasontedor/following{/other_user}","gists_url":"https://api.github.com/users/jasontedor/gists{/gist_id}","starred_url":"https://api.github.com/users/jasontedor/starred{/owner}{/repo}","subscriptions_url":"https://api.github.com/users/jasontedor/subscriptions","organizations_url":"https://api.github.com/users/jasontedor/orgs","repos_url":"https://api.github.com/users/jasontedor/repos","events_url":"https://api.github.com/users/jasontedor/events{/privacy}","received_events_url":"https://api.github.com/users/jasontedor/received_events","type":"User","site_admin":false},"repo":{"id":38618383,"name":"elasticsearch","full_name":"jasontedor/elasticsearch","owner":{"login":"jasontedor","id":4744941,"avatar_url":"https://avatars.githubusercontent.com/u/4744941?v=3","gravatar_id":"","url":"https://api.github.com/users/jasontedor","html_url":"https://github.com/jasontedor","followers_url":"https://api.github.com/users/jasontedor/followers","following_url":"https://api.github.com/users/jasontedor/following{/other_user}","gists_url":"https://api.github.com/users/jasontedor/gists{/gist_id}","starred_url":"https://api.github.com/users/jasontedor/starred{/owner}{/repo}","subscriptions_url":"https://api.github.com/users/jasontedor/subscriptions","organizations_url":"https://api.github.com/users/jasontedor/orgs","repos_url":"https://api.github.com/users/jasontedor/repos","events_url":"https://api.github.com/users/jasontedor/events{/privacy}","received_events_url":"https://api.github.com/users/jasontedor/received_events","type":"User","site_admin":false},"private":false,"html_url":"https://github.com/jasontedor/elasticsearch","description":"Open 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