Copyright 2015 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.
/**
 * Copyright 2015 Netflix, Inc.
 * <p/>
 * 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
 * <p/>
 * http://www.apache.org/licenses/LICENSE-2.0
 * <p/>
 * 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.hystrix.metric.consumer;

import com.netflix.hystrix.HystrixCommandKey;
import com.netflix.hystrix.HystrixCommandProperties;
import com.netflix.hystrix.metric.HystrixCommandStartStream;

import java.util.concurrent.ConcurrentHashMap;
import java.util.concurrent.ConcurrentMap;

Maintains a stream of the maximum concurrency seen by this command. This gets calculated using a rolling window of t1 milliseconds. This window has b buckets. Therefore, a new rolling-max is produced every t2 (=t1/b) milliseconds t1 = HystrixCommandProperties.metricsRollingStatisticalWindowInMilliseconds() b = HystrixCommandProperties.metricsRollingStatisticalWindowBuckets() This value gets cached in this class. It may be queried using RollingConcurrencyStream.getLatestRollingMax() This value is stable - there's no peeking into a bucket until it is emitted /**
 * Maintains a stream of the maximum concurrency seen by this command.
 *
 * This gets calculated using a rolling window of t1 milliseconds.  This window has b buckets.
 * Therefore, a new rolling-max is produced every t2 (=t1/b) milliseconds
 * t1 = {@link HystrixCommandProperties#metricsRollingStatisticalWindowInMilliseconds()}
 * b = {@link HystrixCommandProperties#metricsRollingStatisticalWindowBuckets()}
 *
 * This value gets cached in this class.  It may be queried using {@link #getLatestRollingMax()}
 * This value is stable - there's no peeking into a bucket until it is emitted
 *
 */
public class RollingCommandMaxConcurrencyStream extends RollingConcurrencyStream {

    private static final ConcurrentMap<String, RollingCommandMaxConcurrencyStream> streams = new ConcurrentHashMap<String, RollingCommandMaxConcurrencyStream>();

    public static RollingCommandMaxConcurrencyStream getInstance(HystrixCommandKey commandKey, HystrixCommandProperties properties) {
        final int counterMetricWindow = properties.metricsRollingStatisticalWindowInMilliseconds().get();
        final int numCounterBuckets = properties.metricsRollingStatisticalWindowBuckets().get();
        final int counterBucketSizeInMs = counterMetricWindow / numCounterBuckets;

        return getInstance(commandKey, numCounterBuckets, counterBucketSizeInMs);
    }

    public static RollingCommandMaxConcurrencyStream getInstance(HystrixCommandKey commandKey, int numBuckets, int bucketSizeInMs) {
        RollingCommandMaxConcurrencyStream initialStream = streams.get(commandKey.name());
        if (initialStream != null) {
            return initialStream;
        } else {
            synchronized (RollingCommandMaxConcurrencyStream.class) {
                RollingCommandMaxConcurrencyStream existingStream = streams.get(commandKey.name());
                if (existingStream == null) {
                    RollingCommandMaxConcurrencyStream newStream = new RollingCommandMaxConcurrencyStream(commandKey, numBuckets, bucketSizeInMs);
                    streams.putIfAbsent(commandKey.name(), newStream);
                    return newStream;
                } else {
                    return existingStream;
                }
            }
        }
    }

    public static void reset() {
        streams.clear();
    }

    private RollingCommandMaxConcurrencyStream(final HystrixCommandKey commandKey, final int numBuckets, final int bucketSizeInMs) {
        super(HystrixCommandStartStream.getInstance(commandKey), numBuckets, bucketSizeInMs);
    }
}