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The Amazon Web Services SDK for Java provides Java APIs for building software on AWS' cost-effective, scalable, and reliable infrastructure products. The AWS Java SDK allows developers to code against APIs for all of Amazon's infrastructure web services (Amazon S3, Amazon EC2, Amazon SQS, Amazon Relational Database Service, Amazon AutoScaling, etc).
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/*
 * Copyright 2010-2014 Amazon.com, Inc. or its affiliates. All Rights Reserved.
 *
 * Licensed under the Apache License, Version 2.0 (the "License").
 * You may not use this file except in compliance with the License.
 * A copy of the License is located at
 *
 *  http://aws.amazon.com/apache2.0
 *
 * or in the "license" file accompanying this file. This file 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.amazonaws.metrics.internal.cloudwatch;

import java.util.concurrent.BlockingQueue;
import java.util.concurrent.LinkedBlockingQueue;

import org.apache.commons.logging.Log;
import org.apache.commons.logging.LogFactory;
import org.apache.http.annotation.ThreadSafe;

import com.amazonaws.metrics.MetricCollector;
import com.amazonaws.metrics.RequestMetricCollector;
import com.amazonaws.metrics.ServiceMetricCollector;
import com.amazonaws.services.cloudwatch.AmazonCloudWatchClient;
import com.amazonaws.services.cloudwatch.model.MetricDatum;

/**
 * This is the default implementation of an AWS SDK request metric collection
 * system.
 * 
 * @see RequestMetricCollector
 */
@ThreadSafe
public class MetricCollectorSupport extends MetricCollector {
    protected final static Log log = LogFactory.getLog(MetricCollectorSupport.class);
    private static volatile MetricCollectorSupport singleton;
    
    /** Returns the singleton instance; or null if there isn't one. */
    static MetricCollectorSupport getInstance() {
        return singleton;
    }

    /** 
     * Starts a new CloudWatch collector if it's not already started.
     *
     * @return true if it is successfully started by this call; false if the
     * collector is already running or if there is failure in trying to start
     * the collector for the first time. 
     */
    static synchronized boolean startSingleton(CloudWatchMetricConfig config) {
        if (singleton != null) {
            return false;
        }
        log.info("Initializing " + MetricCollectorSupport.class.getSimpleName());
        return createAndStartCollector(config);
    }

    /** Retarts with a new CloudWatch collector. */
    static synchronized boolean restartSingleton(CloudWatchMetricConfig config) {
        if (singleton == null) {
            throw new IllegalStateException(MetricCollectorSupport.class.getSimpleName()
                + " has neven been initialized");
        }
        log.info("Re-initializing " + MetricCollectorSupport.class.getSimpleName());
        singleton.stop();
        // singleton is set to null at this point via the stop method
        return createAndStartCollector(config);
    }

    /**
     * Returns true if the collector is successfully created and started;
     * false otherwise.
     */
    private static boolean createAndStartCollector(CloudWatchMetricConfig config) {
        MetricCollectorSupport collector = new MetricCollectorSupport(config);
        if (collector.start()) {
            singleton = collector;
            return true;
        }
        return false;
    }

    private final RequestMetricCollectorSupport requestMetricCollector;
    private final ServiceMetricCollectorSupport serviceMetricCollector;

    private final BlockingQueue queue;
//    private final PredefinedMetricTransformer transformer = new PredefinedMetricTransformer();
    private final CloudWatchMetricConfig config;
    private MetricUploaderThread uploaderThread;

    protected MetricCollectorSupport(CloudWatchMetricConfig config) {
        if (config == null) {
            throw new IllegalArgumentException();
        }
        this.config = config;
        this.queue = new LinkedBlockingQueue(config.getMetricQueueSize());
        this.requestMetricCollector = new RequestMetricCollectorSupport(queue);
        this.serviceMetricCollector = new ServiceMetricCollectorSupport(queue);
    }

    @Override
    public boolean start() {
        synchronized(MetricCollectorSupport.class) {
            if (uploaderThread != null) {
                return false;   // already started
            }
            uploaderThread = new MetricUploaderThread(config, queue);
            uploaderThread.start();
        }
        return true;
    }

    /**
     * Stops this collector immediately, dropping all pending metrics in memory.
     */
    @Override
    public boolean stop() {
        synchronized(MetricCollectorSupport.class) {
            if (uploaderThread != null) {
                uploaderThread.cancel();
                uploaderThread.interrupt();
                uploaderThread = null;
                if (singleton == this) { // defensive check
                    singleton = null;
                }
                return true;
            }
        }
        return false;
    }

    /** Returns the configuration. */
    public CloudWatchMetricConfig getConfig() { return config; }

    public AmazonCloudWatchClient getCloudwatchClient() {
        return uploaderThread == null ? null : uploaderThread.getCloudwatchClient();
    }
    /** Always returns true. */
    @Override public final boolean isEnabled() { return true; }

    @Override
    public RequestMetricCollector getRequestMetricCollector() {
        return requestMetricCollector;
    }

    @Override 
    public ServiceMetricCollector getServiceMetricCollector() {
        return serviceMetricCollector;
    }
}