/**
* 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.waveprotocol.wave.model.util;
import org.waveprotocol.wave.model.util.FuzzingBackOffGenerator.BackOffParameters;
/**
* Schedules a task with fuzzing fibonacci backoff schedule. The
* Actual scheduling is delegated to a native scheduler.
* This class does not interpret the delay values, but simply passes
* them through to the native scheduler.
*
* @author zdwang@google.com (David Wang)
*/
public class FuzzingBackOffScheduler implements Scheduler {
/** The scheduled task that can be cancelled */
public interface Cancellable {
/**
* Cancel this task.
*/
void cancel();
}
/**
* Allows injection of actually defer executing a task. This because the
* client and server has different scheduling implementations. A collective
* scheduler tries to executed the task at the given targetTimeMs, but may
* execute the task at minAllowedMs if it is more efficient to do so.
*/
public interface CollectiveScheduler {
/**
* Schedules a task to be executed between minAllowedMs and targetTimeMs
* milliseconds in the future.
*
* @param task the task to execute
* @param minAllowedMs the minimum amount of time to wait.
* @param targetTimeMs the target delay to wait
*/
Cancellable schedule(Command task, int minAllowedMs, int targetTimeMs);
}
private final FuzzingBackOffGenerator generator;
private final CollectiveScheduler scheduler;
private final int maxAttempts;
private Cancellable scheduledTask;
private int attempts = 0;
/**
* @param initialBackOffMs Initial value to back off. This class does not interpret the meaning of
* this value.
* @param maxBackOffMs Max value to back off
* @param randomisationFactor between 0 and 1 to control the range of randomness.
* @param scheduler assumed not null.
* @param maxAttempts maximum number of times to schedule a task
*/
private FuzzingBackOffScheduler(int initialBackOffMs, int maxBackOffMs,
double randomisationFactor, CollectiveScheduler scheduler, int maxAttempts) {
this.generator = new FuzzingBackOffGenerator(initialBackOffMs, maxBackOffMs,
randomisationFactor);
this.scheduler = scheduler;
this.maxAttempts = maxAttempts;
}
@Override
public void reset() {
generator.reset();
if (scheduledTask != null) {
scheduledTask.cancel();
}
scheduledTask = null;
}
@Override
public boolean schedule(Command task) {
if (scheduledTask != null) {
scheduledTask.cancel();
}
if (attempts >= maxAttempts) {
return false;
}
BackOffParameters parameters = generator.next();
scheduledTask = scheduler.schedule(task, parameters.minimumDelay, parameters.targetDelay);
attempts++;
return true;
}
/**
* Builder for FuzzingBackOffSchedulers.
*/
public static class Builder {
private int initialBackOffMs = 10;
private int maxBackOffMs = 5000;
private double randomisationFactor = 0.5;
private final CollectiveScheduler scheduler;
private int maxAttempts = Integer.MAX_VALUE;
/**
* Constructor.
*
* @param scheduler the underlying scheduler to use to actually execute tasks.
*/
public Builder(CollectiveScheduler scheduler) {
this.scheduler = scheduler;
}
/**
* Build the scheduler.
*
* @return the newly created scheduler
*/
public Scheduler build() {
return new FuzzingBackOffScheduler(initialBackOffMs, maxBackOffMs, randomisationFactor,
scheduler, maxAttempts);
}
public Builder setInitialBackOffMs(int initialBackOffMs) {
this.initialBackOffMs = initialBackOffMs;
return this;
}
public Builder setMaxBackOffMs(int maxBackOffMs) {
this.maxBackOffMs = maxBackOffMs;
return this;
}
public Builder setRandomisationFactor(double randomisationFactor) {
this.randomisationFactor = randomisationFactor;
return this;
}
public Builder setMaxAttempts(int maxAttempts) {
this.maxAttempts = maxAttempts;
return this;
}
}
}