| /** |
| * 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.htrace.impl; |
| |
| import java.math.BigInteger; |
| import java.util.concurrent.TimeUnit; |
| |
| /** |
| * Utilities for dealing with monotonic time. |
| */ |
| class TimeUtil { |
| /** |
| * Returns the current monotonic time in milliseconds. |
| */ |
| static long nowMs() { |
| return TimeUnit.MILLISECONDS.convert( |
| System.nanoTime(), TimeUnit.NANOSECONDS); |
| } |
| |
| /** |
| * Get the approximate delta between two monotonic times. |
| * |
| * This function makes the following assumptions: |
| * 1. We read startMs from the monotonic clock prior to endMs. |
| * 2. The two times are not more than 100 years or so apart. |
| * |
| * With these two assumptions in hand, we can smooth over some of the |
| * unpleasant features of the monotonic clock: |
| * 1. It can return either positive or negative values. |
| * 2. When the number of nanoseconds reaches Long.MAX_VALUE it wraps around |
| * to Long.MIN_VALUE. |
| * 3. On some messed up systems it has been known to jump backwards every |
| * now and then. Oops. CPU core synchronization mumble mumble. |
| * |
| * @param startMs The start time. |
| * @param endMs The end time. |
| * @return The delta between the two times. |
| */ |
| static long deltaMs(long startMs, long endMs) { |
| BigInteger startNs = BigInteger.valueOf(TimeUnit.NANOSECONDS. |
| convert(startMs, TimeUnit.MILLISECONDS)); |
| BigInteger endNs = BigInteger.valueOf(TimeUnit.NANOSECONDS. |
| convert(endMs, TimeUnit.MILLISECONDS)); |
| BigInteger deltaNs = endNs.subtract(startNs); |
| if (deltaNs.signum() >= 0) { |
| return TimeUnit.MILLISECONDS.convert(deltaNs.min( |
| BigInteger.valueOf(Long.MAX_VALUE)).longValue(), TimeUnit.NANOSECONDS); |
| } |
| deltaNs = deltaNs.negate(); |
| if (deltaNs.compareTo(BigInteger.valueOf(Long.MAX_VALUE / 2)) < 0) { |
| // If the 'startNs' is numerically less than the 'endNs', and the |
| // difference between the two is less than 100 years, it's probably |
| // just clock jitter. Certain old OSes and CPUs had monotonic clocks |
| // that could go backwards under certain conditions (ironic, given |
| // the name). |
| return 0L; |
| } |
| // Handle rollover. |
| BigInteger revDeltaNs = BigInteger.ONE.shiftLeft(64).subtract(deltaNs); |
| return TimeUnit.MILLISECONDS.convert(revDeltaNs.min( |
| BigInteger.valueOf(Long.MAX_VALUE)).longValue(), TimeUnit.NANOSECONDS); |
| } |
| } |