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The Apache Cassandra Project develops a highly scalable second-generation distributed database, bringing together Dynamo's fully distributed design and Bigtable's ColumnFamily-based data model.
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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 org.apache.cassandra.tracing;

import java.net.InetAddress;
import java.nio.ByteBuffer;
import java.util.UUID;
import java.util.concurrent.TimeUnit;
import java.util.concurrent.atomic.AtomicInteger;

import com.google.common.base.Stopwatch;
import org.slf4j.helpers.MessageFormatter;

import org.apache.cassandra.concurrent.Stage;
import org.apache.cassandra.concurrent.StageManager;
import org.apache.cassandra.config.CFMetaData;
import org.apache.cassandra.db.CFRowAdder;
import org.apache.cassandra.db.ColumnFamily;
import org.apache.cassandra.db.Mutation;
import org.apache.cassandra.utils.ByteBufferUtil;
import org.apache.cassandra.utils.FBUtilities;
import org.apache.cassandra.utils.UUIDGen;
import org.apache.cassandra.utils.WrappedRunnable;

/**
 * ThreadLocal state for a tracing session. The presence of an instance of this class as a ThreadLocal denotes that an
 * operation is being traced.
 */
public class TraceState
{
    public final UUID sessionId;
    public final InetAddress coordinator;
    public final Stopwatch watch;
    public final ByteBuffer sessionIdBytes;

    // Multiple requests can use the same TraceState at a time, so we need to reference count.
    // See CASSANDRA-7626 for more details.
    private final AtomicInteger references = new AtomicInteger(1);

    public TraceState(InetAddress coordinator, UUID sessionId)
    {
        assert coordinator != null;
        assert sessionId != null;

        this.coordinator = coordinator;
        this.sessionId = sessionId;
        sessionIdBytes = ByteBufferUtil.bytes(sessionId);
        watch = Stopwatch.createStarted();
    }

    public int elapsed()
    {
        long elapsed = watch.elapsed(TimeUnit.MICROSECONDS);
        return elapsed < Integer.MAX_VALUE ? (int) elapsed : Integer.MAX_VALUE;
    }

    public void trace(String format, Object arg)
    {
        trace(MessageFormatter.format(format, arg).getMessage());
    }

    public void trace(String format, Object arg1, Object arg2)
    {
        trace(MessageFormatter.format(format, arg1, arg2).getMessage());
    }

    public void trace(String format, Object[] args)
    {
        trace(MessageFormatter.arrayFormat(format, args).getMessage());
    }

    public void trace(String message)
    {
        TraceState.trace(sessionIdBytes, message, elapsed());
    }

    public static void trace(final ByteBuffer sessionIdBytes, final String message, final int elapsed)
    {
        final String threadName = Thread.currentThread().getName();

        StageManager.getStage(Stage.TRACING).execute(new WrappedRunnable()
        {
            public void runMayThrow()
            {
                Mutation mutation = new Mutation(Tracing.TRACE_KS, sessionIdBytes);
                ColumnFamily cells = mutation.addOrGet(CFMetaData.TraceEventsCf);

                CFRowAdder adder = new CFRowAdder(cells, cells.metadata().comparator.make(UUIDGen.getTimeUUID()), FBUtilities.timestampMicros());
                adder.add("activity", message);
                adder.add("source", FBUtilities.getBroadcastAddress());
                if (elapsed >= 0)
                    adder.add("source_elapsed", elapsed);
                adder.add("thread", threadName);

                Tracing.mutateWithCatch(mutation);
            }
        });
    }

    public boolean acquireReference()
    {
        while (true)
        {
            int n = references.get();
            if (n <= 0)
                return false;
            if (references.compareAndSet(n, n + 1))
                return true;
        }
    }

    public int releaseReference()
    {
        return references.decrementAndGet();
    }
}