| /* |
| * Licensed to the Apache Software Foundation (ASF) under one |
| * or more contributor license agreements. See the NOTICE file |
| * distributed with this work for additional information |
| * regarding copyright ownership. The ASF licenses this file |
| * to you 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 org.apache.cassandra.db.monitoring; |
| |
| import java.util.concurrent.TimeUnit; |
| |
| import org.slf4j.Logger; |
| import org.slf4j.LoggerFactory; |
| |
| import org.apache.cassandra.concurrent.ScheduledExecutors; |
| import org.apache.cassandra.config.Config; |
| |
| /** |
| * This is an approximation of System.currentTimeInMillis(). It updates its |
| * time value at periodic intervals of CHECK_INTERVAL_MS milliseconds |
| * (currently 10 milliseconds by default). It can be used as a faster alternative |
| * to System.currentTimeInMillis() every time an imprecision of a few milliseconds |
| * can be accepted. |
| */ |
| public class ApproximateTime |
| { |
| private static final Logger logger = LoggerFactory.getLogger(ApproximateTime.class); |
| private static final int CHECK_INTERVAL_MS = Math.max(5, Integer.parseInt(System.getProperty(Config.PROPERTY_PREFIX + "approximate_time_precision_ms", "10"))); |
| |
| private static volatile long time = System.currentTimeMillis(); |
| static |
| { |
| logger.info("Scheduling approximate time-check task with a precision of {} milliseconds", CHECK_INTERVAL_MS); |
| ScheduledExecutors.scheduledFastTasks.scheduleWithFixedDelay(() -> time = System.currentTimeMillis(), |
| CHECK_INTERVAL_MS, |
| CHECK_INTERVAL_MS, |
| TimeUnit.MILLISECONDS); |
| } |
| |
| public static long currentTimeMillis() |
| { |
| return time; |
| } |
| |
| public static long precision() |
| { |
| return 2 * CHECK_INTERVAL_MS; |
| } |
| |
| } |