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/**
 * 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.twitter.distributedlog.readahead;

import com.twitter.distributedlog.ReadAheadCache;
import org.apache.bookkeeper.stats.Gauge;
import org.apache.bookkeeper.stats.StatsLogger;

import java.util.concurrent.atomic.AtomicLong;

/**
 * ReadAheadTracker is tracking the progress of readahead worker. so we could use it to investigate where
 * the readahead worker is.
 */
public class ReadAheadTracker {
    // ticks is used to differentiate that the worker enter same phase in different time.
    final AtomicLong ticks = new AtomicLong(0);
    // which phase that the worker is in.
    ReadAheadPhase phase;

    ReadAheadTracker(String streamName,
                     final ReadAheadCache cache,
                     ReadAheadPhase initialPhase,
                     StatsLogger statsLogger) {
        this.phase = initialPhase;
        statsLogger.registerGauge("phase", new Gauge() {
            @Override
            public Number getDefaultValue() {
                return ReadAheadPhase.SCHEDULE_READAHEAD.getCode();
            }

            @Override
            public Number getSample() {
                return phase.getCode();
            }
        });
        statsLogger.registerGauge("ticks", new Gauge() {
            @Override
            public Number getDefaultValue() {
                return 0;
            }

            @Override
            public Number getSample() {
                return ticks.get();
            }
        });
        statsLogger.registerGauge("cache_entries", new Gauge() {
            @Override
            public Number getDefaultValue() {
                return 0;
            }

            @Override
            public Number getSample() {
                return cache.getNumCachedRecords();
            }
        });
    }

    ReadAheadPhase getPhase() {
        return this.phase;
    }

    public void enterPhase(ReadAheadPhase readAheadPhase) {
        this.ticks.incrementAndGet();
        this.phase = readAheadPhase;
    }
}