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/**
 * Copyright 2013 Netflix, Inc.
 *
 * Licensed 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.netflix.servo.publish;

import com.netflix.servo.util.UnmodifiableList;
import com.netflix.servo.Metric;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;

import java.util.ArrayList;
import java.util.Collections;
import java.util.HashMap;
import java.util.List;
import java.util.Map;
import java.util.concurrent.ExecutionException;
import java.util.concurrent.ExecutorService;
import java.util.concurrent.Future;
import java.util.concurrent.TimeUnit;
import java.util.concurrent.TimeoutException;

/**
 * Combines results from a list of metric pollers. This clas
 */
public class CompositeMetricPoller implements MetricPoller {

    private static final Logger LOGGER = LoggerFactory.getLogger(CompositeMetricPoller.class);

    private static final List EMPTY = UnmodifiableList.of();

    private static final String POLLER_KEY = "PollerName";

    private final Map pollers;
    private final ExecutorService executor;
    private final long timeout;

    /**
     * Creates a new instance for a set of pollers.
     *
     * @param pollers   a set of pollers to collect data from, the map key for a
     *                  poller is used as a name identify a particular poller
     *                  for logging and error messages
     * @param executor  an executor to use for executing the poll methods
     * @param timeout   timeout in milliseconds used when getting the value
     *                  from the future
     */
    public CompositeMetricPoller(
            Map pollers, ExecutorService executor, long timeout) {
        this.pollers = Collections.unmodifiableMap(pollers);
        this.executor = executor;
        this.timeout = timeout;
    }

    private void increment(Throwable t, String name) {
        //TagList tags = SortedTagList.builder().withTag(new BasicTag(POLLER_KEY, name)).build();
        //Counters.increment(t.getClass().getSimpleName() + "Count", tags);
    }

    private List getMetrics(String name, Future> future) {
        List metrics = EMPTY;
        try {
            metrics = future.get(timeout, TimeUnit.MILLISECONDS);
        } catch (ExecutionException e) {
            increment(e, name);
            LOGGER.warn("uncaught exception from poll method for " + name, e);
        } catch (TimeoutException e) {
            // The cancel is needed to prevent the slow task from using up all threads
            future.cancel(true);
            increment(e, name);
            LOGGER.warn("timeout executing poll method for " + name, e);
        } catch (InterruptedException e) {
            increment(e, name);
            LOGGER.warn("interrupted while doing get for " + name, e);
        }
        return metrics;
    }

    /** {@inheritDoc} */
    public final List poll(MetricFilter filter) {
        return poll(filter, false);
    }

    /** {@inheritDoc} */
    public final List poll(MetricFilter filter, boolean reset) {
        Map>> futures = new HashMap>>();
        for (Map.Entry e : pollers.entrySet()) {
            PollCallable task = new PollCallable(e.getValue(), filter, reset);
            futures.put(e.getKey(), executor.submit(task));
        }

        List allMetrics = new ArrayList();
        for (Map.Entry>> e : futures.entrySet()) {
            allMetrics.addAll(getMetrics(e.getKey(), e.getValue()));
        }
        return allMetrics;
    }
}