1/*
2 * Licensed to the Apache Software Foundation (ASF) under one or more
3 * contributor license agreements.  See the NOTICE file distributed with
4 * this work for additional information regarding copyright ownership.
5 * The ASF licenses this file to You under the Apache License, Version 2.0
6 * (the "License"); you may not use this file except in compliance with
7 * the License.  You may obtain a copy of the License at
8 *
9 *    http://www.apache.org/licenses/LICENSE-2.0
10 *
11 * Unless required by applicable law or agreed to in writing, software
12 * distributed under the License is distributed on an "AS IS" BASIS,
13 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
14 * See the License for the specific language governing permissions and
15 * limitations under the License.
16 */
17
18package org.apache.spark.util
19
20/**
21 * An interface to represent clocks, so that they can be mocked out in unit tests.
22 */
23private[spark] trait Clock {
24  def getTimeMillis(): Long
25  def waitTillTime(targetTime: Long): Long
26}
27
28/**
29 * A clock backed by the actual time from the OS as reported by the `System` API.
30 */
31private[spark] class SystemClock extends Clock {
32
33  val minPollTime = 25L
34
35  /**
36   * @return the same time (milliseconds since the epoch)
37   *         as is reported by `System.currentTimeMillis()`
38   */
39  def getTimeMillis(): Long = System.currentTimeMillis()
40
41  /**
42   * @param targetTime block until the current time is at least this value
43   * @return current system time when wait has completed
44   */
45  def waitTillTime(targetTime: Long): Long = {
46    var currentTime = 0L
47    currentTime = System.currentTimeMillis()
48
49    var waitTime = targetTime - currentTime
50    if (waitTime <= 0) {
51      return currentTime
52    }
53
54    val pollTime = math.max(waitTime / 10.0, minPollTime).toLong
55
56    while (true) {
57      currentTime = System.currentTimeMillis()
58      waitTime = targetTime - currentTime
59      if (waitTime <= 0) {
60        return currentTime
61      }
62      val sleepTime = math.min(waitTime, pollTime)
63      Thread.sleep(sleepTime)
64    }
65    -1
66  }
67}
68