api/src/main/java/org/apache/edgent/oplet/core/PeriodicSource.java

/*
Licensed to the Apache Software Foundation (ASF) under one
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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

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"AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
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specific language governing permissions and limitations
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*/
package org.apache.edgent.oplet.core;

import java.util.concurrent.ScheduledExecutorService;
import java.util.concurrent.ScheduledFuture;
import java.util.concurrent.TimeUnit;

import org.apache.edgent.execution.mbeans.PeriodMXBean;
import org.apache.edgent.execution.services.ControlService;
import org.apache.edgent.oplet.OpletContext;
import org.apache.edgent.oplet.OutputPortContext;

public abstract class PeriodicSource<T> extends Source<T> implements Runnable, PeriodMXBean {
  
    // see comment in TStream.TYPE
    private static final String TSTREAM_TYPE = /*TStream.TYPE*/"stream";

    private long period;
    private TimeUnit unit;
    private ScheduledFuture<?> future;

    protected PeriodicSource(long period, TimeUnit unit) {
        this.period = period;
        this.unit = unit;
    }

    @Override
    public void initialize(OpletContext<Void, T> context) {
        super.initialize(context);
    }

    @Override
    public synchronized void start() {
        ControlService cs = getOpletContext().getService(ControlService.class);
        // TODO BUG HERE: the control alias needs to be unique across the
        // entire provider instance (multiple topologies) because the ControlService
        // is provider-wide, not org.apache.edgent.org.apache.edgent.topology specific.
        // Scope it with just the jobId.  What's going to unregister this control?
        if (cs != null)
            cs.registerControl(TSTREAM_TYPE, getOpletContext().uniquify(getClass().getSimpleName()), 
                    getAlias(), PeriodMXBean.class, this);
        schedule(false);
    }
    
    private String getAlias() {
        OutputPortContext oc = getOpletContext().getOutputContext().get(0);
        return oc.getAlias();
    }

    private synchronized void schedule(boolean delay) {
        future = getOpletContext().getService(ScheduledExecutorService.class).scheduleAtFixedRate(
                getRunnable(), delay ? getPeriod() : 0, getPeriod(), getUnit());
    }

    protected Runnable getRunnable() {
        return this;
    }

    protected abstract void fetchTuples() throws Exception;

    @Override
    public void run() {
        try {
            fetchTuples();
        } catch (Exception e) {
            throw new RuntimeException(e);
        }
    }

    @Override
    public synchronized long getPeriod() {
        return period;
    }

    @Override
    public synchronized TimeUnit getUnit() {
        return unit;
    }

    @Override
    public synchronized void setPeriod(long period) {
        setPeriod(period, getUnit());
    }

    @Override
    public synchronized void setPeriod(long period, TimeUnit unit) {
        if (period <= 0)
            throw new IllegalArgumentException();
        if (this.period != period || this.unit != unit) {
            future.cancel(false);
            this.period = period;
            this.unit = unit;
            schedule(true);
        }  
    }
}