2 * Copyright (c) 2016 Cisco Systems, Inc. and others. All rights reserved.
4 * This program and the accompanying materials are made available under the
5 * terms of the Eclipse Public License v1.0 which accompanies this distribution,
6 * and is available at http://www.eclipse.org/legal/epl-v10.html
9 package org.opendaylight.controller.cluster.access.client;
11 import java.util.concurrent.TimeUnit;
14 * A ProgressTracker subclass which uses {@code ticksWorkedPerClosedTask} to compute delays.
16 * <p>This class has {@code tasksOpenLimit} used as a (weak) limit,
17 * as number of open tasks approaches that value, delays computed are increasing.
19 * <p>In order to keep {@code estimateIsolatedDelay} values from raising unreasonably high,
20 * {@code defaultTicksPerTask} acts as a maximal value. {@code openTask} may return
21 * higher value if there are tasks above the limit.
23 * <p>On the other hand, there is no delay when number of open tasks is half the limit or less,
24 * in order to prevent backend from running out of tasks while there may be waiting frontend threads.
27 * This class is NOT thread-safe.
29 * @author Vratko Polak
31 final class AveragingProgressTracker extends ProgressTracker {
32 private static final long DEFAULT_TICKS_PER_TASK = TimeUnit.MILLISECONDS.toNanos(500);
35 * The implementation will avoid having more that this number of tasks open.
37 private final long tasksOpenLimit;
40 * We do not delay tasks until their count hits this threshold.
42 private final long noDelayThreshold;
45 * Create an idle tracker with limit and specified ticks per task value to use as default.
47 * @param limit of open tasks to avoid exceeding
48 * @param ticksPerTask value to use as default
50 private AveragingProgressTracker(final long limit, final long ticksPerTask) {
52 tasksOpenLimit = limit;
53 noDelayThreshold = limit / 2;
57 * Create a default idle tracker with given limit.
59 * @param limit of open tasks to avoid exceeding
61 AveragingProgressTracker(final long limit) {
62 this(limit, DEFAULT_TICKS_PER_TASK);
66 * Construct a new tracker suitable for a new task queue related to a "reconnect".
68 * <p>The limit is set independently of the old tracker.
70 * @param oldTracker the tracker used for the previously used backend
71 * @param limit of open tasks to avoid exceeding
72 * @param now tick number corresponding to caller's present
74 AveragingProgressTracker(final ProgressTracker oldTracker, final long limit, final long now) {
75 super(oldTracker, now);
76 tasksOpenLimit = limit;
77 noDelayThreshold = limit / 2;
81 * Construct a new tracker suitable for a new task queue related to a "reconnect".
83 * <p>The limit is copied from the old tracker.
85 * @param oldTracker the tracker used for the previously used backend
86 * @param now tick number corresponding to caller's present
88 AveragingProgressTracker(final AveragingProgressTracker oldTracker, final long now) {
89 this(oldTracker, oldTracker.tasksOpenLimit, now);
92 // Protected read-only methods
95 * Give an estimate of a fair delay, assuming delays caused by other opened tasks are ignored.
97 * <p>This implementation returns zero delay if number of open tasks is half of limit or less.
98 * Else the delay is computed, aiming to keep number of open tasks at 3/4 of limit,
99 * assuming backend throughput remains constant.
101 * <p>As the number of open tasks approaches the limit,
102 * the computed delay increases, but it never exceeds defaultTicksPerTask.
103 * That means the actual number of open tasks can exceed the limit.
105 * @param now tick number corresponding to caller's present
106 * @return delay (in ticks) after which another openTask() would be fair to be called by the same thread again
109 protected long estimateIsolatedDelay(final long now) {
110 final long open = tasksOpen();
111 if (open <= noDelayThreshold) {
114 if (open >= tasksOpenLimit) {
115 return defaultTicksPerTask();
119 * Calculate the task capacity relative to the limit on open tasks. In real terms this value can be
120 * in the open interval (0.0, 0.5).
122 final double relativeRemainingCapacity = 1.0 - (double) open / tasksOpenLimit;
125 * Calculate delay coefficient. It increases in inverse proportion to relative remaining capacity, approaching
126 * infinity as remaining capacity approaches 0.0.
128 final double delayCoefficient = (0.5 - relativeRemainingCapacity) / relativeRemainingCapacity;
129 final long delay = (long) (ticksWorkedPerClosedTask(now) * delayCoefficient);
132 * Cap the result to defaultTicksPerTask, since the calculated delay may overstep it.
134 return Math.min(delay, defaultTicksPerTask());