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Scheduler of java processes that seeks to optimize the execution of processing tasks by the JVM with minimal threads in order to reduce the overhead of context switching, optimize the utilization of CPU cores, and provide controls to the application over the scheduling of processing tasks.

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/*
 *   Copyright 2015 AML Innovation & Consulting LLC
 *
 *   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 com.amlinv.javasched.process;

import com.amlinv.javasched.SchedulerProcess;
import com.amlinv.javasched.Step;

/**
 * Scheduler Process that repeats the same step on every request, optionally limited to execution
 * only when signaled.  An example use-case is aggregation of values that are periodically polled.
 *
 * Created by art on 6/5/15.
 */
public class SingleRepeatingStepProcess implements SchedulerProcess {
  private final Step repeatableStep;

  private final Object signalSync = new Object();

  private boolean repeatOnlyWhenSignalled = true;
  private long numSignal = 0;
  private long executionStartedSignalCount = 0;
  private WaitForSignalStep waitForSignalStep = new WaitForSignalStep();

  private boolean stopped = false;

  public SingleRepeatingStepProcess(Step repeatableStep, boolean repeatOnlyWhenSignalled) {
    this.repeatableStep = repeatableStep;
    this.repeatOnlyWhenSignalled = repeatOnlyWhenSignalled;
  }

  public SingleRepeatingStepProcess(Step repeatableStep) {
    this.repeatableStep = repeatableStep;
  }

  public boolean isRepeatOnlyWhenSignalled() {
    return repeatOnlyWhenSignalled;
  }

  public void setRepeatOnlyWhenSignalled(boolean repeatOnlyWhenSignalled) {
    this.repeatOnlyWhenSignalled = repeatOnlyWhenSignalled;
  }

  public void signal() {
    synchronized (this.signalSync) {
      this.numSignal++;
      this.signalSync.notifyAll();
    }
  }

  public void shutdown() {
    synchronized (this.signalSync) {
      this.stopped = true;
      this.signalSync.notifyAll();
    }
  }

  @Override
  public Step getNextStep() {
    if (this.stopped) {
      return null;
    }

    boolean repeatNow = false;
    if (this.repeatOnlyWhenSignalled) {
      if (this.numSignal > this.executionStartedSignalCount) {
        repeatNow = true;
      }
    } else {
      repeatNow = true;
    }

    Step result;
    if (repeatNow) {
      this.executionStartedSignalCount = this.numSignal;
      result = repeatableStep;
    } else {
      result = waitForSignalStep;
    }
    return result;
  }


  ////////////////////
  // INTERNAL CLASSES
  ////////////////////

  protected class WaitForSignalStep implements Step {
    SingleRepeatingStepProcess parent = SingleRepeatingStepProcess.this;

    @Override
    public void execute() {
      synchronized (parent.signalSync) {
        while ((parent.numSignal <= parent.executionStartedSignalCount) && (!parent.stopped)) {
          try {
            parent.signalSync.wait();
          } catch (InterruptedException intExc) {
            throw new RuntimeException("process interrupted", intExc);
          }
        }
      }
    }

    @Override
    public boolean isBlocking() {
      return true;
    }
  }
}