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Input/output abstraction layer for Neo4j.
There is a newer version: 2025.02.0
/*
 * Copyright (c) 2002-2016 "Neo Technology,"
 * Network Engine for Objects in Lund AB [http://neotechnology.com]
 *
 * This file is part of Neo4j.
 *
 * Neo4j is free software: you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation, either version 3 of the License, or
 * (at your option) any later version.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with this program.  If not, see .
 */
package org.neo4j.io.pagecache.tracing;

import java.io.File;
import java.io.IOException;
import java.lang.invoke.MethodHandle;
import java.lang.invoke.MethodHandles;
import java.lang.invoke.MethodType;
import java.lang.invoke.SwitchPoint;
import java.util.concurrent.atomic.AtomicLong;

import org.neo4j.io.pagecache.PageSwapper;

import static org.neo4j.unsafe.impl.internal.dragons.FeatureToggles.packageFlag;

/**
 * The default PageCacheTracer implementation, that just increments counters.
 */
public class DefaultPageCacheTracer implements PageCacheTracer
{
    private static final MethodHandle beginPinMH;
    private static final SwitchPoint beginPinSwitchPoint;
    static
    {
        try
        {
            // A hidden setting to have pin/unpin monitoring enabled from the start by default.
            // NOTE: This flag is documented in jmx.asciidoc
            boolean alwaysEnabled = packageFlag( DefaultPageCacheTracer.class, "tracePinUnpin", false );

            MethodType type = MethodType.methodType( PinEvent.class );
            MethodHandles.Lookup lookup = MethodHandles.lookup();
            MethodHandle monitoredPinMH = lookup.findVirtual( DefaultPageCacheTracer.class, "beginTracingPin", type );
            if ( alwaysEnabled )
            {
                beginPinMH = monitoredPinMH;
                beginPinSwitchPoint = null;
            }
            else
            {
                MethodHandle nullPinMH = lookup.findVirtual( DefaultPageCacheTracer.class, "beginNullPin", type );
                beginPinSwitchPoint = new SwitchPoint();
                beginPinMH = beginPinSwitchPoint.guardWithTest( nullPinMH, monitoredPinMH );
            }
        }
        catch ( Exception e )
        {
            throw new AssertionError( "Unexpected MethodHandle initiation error", e );
        }
    }

    /**
     * Enable monitoring of page pins and unpins, which is disabled by default for
     * performance reasons.
     *
     * This is a one-way operation; once monitoring of pinning and unpinning has been
     * enabled, it cannot be disabled again without restarting the JVM.
     */
    public static void enablePinUnpinTracing()
    {
        if ( beginPinSwitchPoint != null && !beginPinSwitchPoint.hasBeenInvalidated() )
        {
            SwitchPoint.invalidateAll( new SwitchPoint[]{ beginPinSwitchPoint } );
        }
    }

    protected final AtomicLong faults = new AtomicLong();
    protected final AtomicLong evictions = new AtomicLong();
    protected final AtomicLong pins = new AtomicLong();
    protected final AtomicLong unpins = new AtomicLong();
    protected final AtomicLong flushes = new AtomicLong();
    protected final AtomicLong bytesRead = new AtomicLong();
    protected final AtomicLong bytesWritten = new AtomicLong();
    protected final AtomicLong filesMapped = new AtomicLong();
    protected final AtomicLong filesUnmapped = new AtomicLong();
    protected final AtomicLong evictionExceptions = new AtomicLong();

    private final FlushEvent flushEvent = new FlushEvent()
    {
        @Override
        public void addBytesWritten( long bytes )
        {
            bytesWritten.getAndAdd( bytes );
        }

        @Override
        public void done()
        {
            flushes.getAndIncrement();
        }

        @Override
        public void done( IOException exception )
        {
            done();
        }

        @Override
        public void addPagesFlushed( int pageCount )
        {
        }
    };

    private final FlushEventOpportunity flushEventOpportunity = new FlushEventOpportunity()
    {
        @Override
        public FlushEvent beginFlush( long filePageId, int cachePageId, PageSwapper swapper )
        {
            return flushEvent;
        }
    };

    private final EvictionEvent evictionEvent = new EvictionEvent()
    {
        @Override
        public void setFilePageId( long filePageId )
        {
        }

        @Override
        public void setSwapper( PageSwapper swapper )
        {
        }

        @Override
        public FlushEventOpportunity flushEventOpportunity()
        {
            return flushEventOpportunity;
        }

        @Override
        public void threwException( IOException exception )
        {
            evictionExceptions.getAndIncrement();
        }

        @Override
        public void setCachePageId( int cachePageId )
        {
        }

        @Override
        public void close()
        {
            evictions.getAndIncrement();
        }
    };

    private final EvictionRunEvent evictionRunEvent = new EvictionRunEvent()
    {
        @Override
        public EvictionEvent beginEviction()
        {
            return evictionEvent;
        }

        @Override
        public void close()
        {
        }
    };

    private final PageFaultEvent pageFaultEvent = new PageFaultEvent()
    {
        @Override
        public void addBytesRead( long bytes )
        {
            bytesRead.getAndAdd( bytes );
        }

        @Override
        public void done()
        {
            faults.getAndIncrement();
        }

        @Override
        public void done( Throwable throwable )
        {
            done();
        }

        @Override
        public EvictionEvent beginEviction()
        {
            return evictionEvent;
        }

        @Override
        public void setCachePageId( int cachePageId )
        {
        }
    };

    private final PinEvent pinTracingEvent = new PinEvent()
    {
        @Override
        public void setCachePageId( int cachePageId )
        {
        }

        @Override
        public PageFaultEvent beginPageFault()
        {
            return pageFaultEvent;
        }

        @Override
        public void done()
        {
            unpins.getAndIncrement();
        }
    };

    private final PinEvent nullPinEvent = new PinEvent()
    {
        @Override
        public void setCachePageId( int cachePageId )
        {
        }

        @Override
        public PageFaultEvent beginPageFault()
        {
            return pageFaultEvent;
        }

        @Override
        public void done()
        {
        }
    };

    private final MajorFlushEvent majorFlushEvent = new MajorFlushEvent()
    {
        @Override
        public FlushEventOpportunity flushEventOpportunity()
        {
            return flushEventOpportunity;
        }

        @Override
        public void close()
        {
        }
    };

    @Override
    public void mappedFile( File file )
    {
        filesMapped.getAndIncrement();
    }

    @Override
    public void unmappedFile( File file )
    {
        filesUnmapped.getAndIncrement();
    }

    @Override
    public EvictionRunEvent beginPageEvictions( int pageCountToEvict )
    {
        return evictionRunEvent;
    }

    @Override
    public PinEvent beginPin( boolean writeLock, long filePageId, PageSwapper swapper )
    {
        try
        {
            return (PinEvent) beginPinMH.invokeExact( this );
        }
        catch ( Throwable throwable )
        {
            throw new AssertionError( "Unexpected MethodHandle error", throwable );
        }
    }

    /**
     * Invoked through beginPinMH.
     */
    @SuppressWarnings( "UnusedDeclaration" )
    private PinEvent beginNullPin()
    {
        return nullPinEvent;
    }

    /**
     * Invoked through beginPinMH.
     */
    @SuppressWarnings( "UnusedDeclaration" )
    private PinEvent beginTracingPin()
    {
        pins.getAndIncrement();
        return pinTracingEvent;
    }

    @Override
    public MajorFlushEvent beginFileFlush( PageSwapper swapper )
    {
        return majorFlushEvent;
    }

    @Override
    public MajorFlushEvent beginCacheFlush()
    {
        return majorFlushEvent;
    }

    @Override
    public long faults()
    {
        return faults.get();
    }

    @Override
    public long evictions()
    {
        return evictions.get();
    }

    @Override
    public long pins()
    {
        return pins.get();
    }

    @Override
    public long unpins()
    {
        return unpins.get();
    }

    @Override
    public long flushes()
    {
        return flushes.get();
    }

    @Override
    public long bytesRead()
    {
        return bytesRead.get();
    }

    @Override
    public long bytesWritten()
    {
        return bytesWritten.get();
    }

    @Override
    public long filesMapped()
    {
        return filesMapped.get();
    }

    @Override
    public long filesUnmapped()
    {
        return filesUnmapped.get();
    }

    @Override
    public long evictionExceptions()
    {
        return evictionExceptions.get();
    }
}