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TicketedProcessing.java
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TicketedProcessing.java
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/*
* 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 <http://www.gnu.org/licenses/>.
*/
package org.neo4j.unsafe.impl.batchimport.staging;
import java.util.Iterator;
import java.util.concurrent.ArrayBlockingQueue;
import java.util.concurrent.Future;
import java.util.concurrent.atomic.AtomicLong;
import java.util.function.BiFunction;
import java.util.function.LongPredicate;
import java.util.function.Supplier;
import org.neo4j.unsafe.impl.batchimport.Parallelizable;
import org.neo4j.unsafe.impl.batchimport.executor.DynamicTaskExecutor;
import org.neo4j.unsafe.impl.batchimport.executor.ParkStrategy;
import org.neo4j.unsafe.impl.batchimport.executor.TaskExecutor;
import static java.util.concurrent.TimeUnit.MILLISECONDS;
import static org.neo4j.helpers.FutureAdapter.future;
import static org.neo4j.unsafe.impl.batchimport.staging.Processing.await;
/**
* Accepts jobs and processes them, potentially in parallel. Each task is given a ticket, an incrementing
* integer where results of processed tasks are {@link #next() returned} in the order of ticket,
* i.e. in order of submission. Number of threads processing jobs can be controlled via methods from
* {@link Parallelizable}. This little ASCII image will make an attempt to visualize this simple flow.
*
* <pre>
* Processors...
* ┌────┐
* ┌─>│Job ├──┐
* │ └────┘ │
* ┌────────────────┐ │ ┌────┐ │ ┌─────────────────┐
* │Submitted jobs ├──┼─>│Job ├──┼─>│Processed jobs │
* └────────────────┘ │ └────┘ │ └─────────────────┘
* │ ┌────┐ │
* └─>│Job ├──┘
* └────┘
* </pre>
*
* For easily spawning a thread sitting and submitting jobs to be processed from an {@link Iterator},
* see {@link #slurp(Iterator, boolean)}.
*
* @param <FROM> raw material to process
* @param <STATE> thread local state that each processing thread will share between jobs
* @param <TO> result that a raw material will be processed into
*/
public class TicketedProcessing<FROM,STATE,TO> implements Parallelizable
{
private static final ParkStrategy park = new ParkStrategy.Park( 10, MILLISECONDS );
private final TaskExecutor<STATE> executor;
private final BiFunction<FROM,STATE,TO> processor;
private final ArrayBlockingQueue<TO> processed;
private final AtomicLong submittedTicket = new AtomicLong( -1 );
private final AtomicLong processedTicket = new AtomicLong( -1 );
private final LongPredicate myTurnToAddToProcessedQueue = new LongPredicate()
{
@Override
public boolean test( long ticket )
{
return processedTicket.get() == ticket - 1;
}
};
private final LongPredicate catchUp = new LongPredicate()
{
@Override
public boolean test( long ticket )
{
long queued = submittedTicket.get() - processedTicket.get();
return queued <= executor.processors( 0 );
}
};
private final Runnable healthCheck;
private volatile boolean done;
public TicketedProcessing( String name, int maxProcessors, BiFunction<FROM,STATE,TO> processor,
Supplier<STATE> threadLocalStateSupplier )
{
this.processor = processor;
this.executor = new DynamicTaskExecutor<>( 1, maxProcessors, maxProcessors, park, name,
threadLocalStateSupplier );
this.healthCheck = executor::assertHealthy;
this.processed = new ArrayBlockingQueue<>( maxProcessors );
}
/**
* Submits a job for processing. Results from processed jobs will be available from {@link #next()}
* in the order in which they got submitted. This method will queue jobs for processing, but not
* more than the number of current processors and never more than number of maximum processors
* given in the constructor; the call will block until queue size goes under this threshold.
* Blocking will provide push-back of submitting new jobs as to reduce unnecessary memory requirements
* for jobs that will sit and wait to be processed.
*
* @param job to process.
*/
public void submit( FROM job )
{
long ticket = submittedTicket.incrementAndGet();
await( catchUp, ticket, healthCheck, park );
executor.submit( threadLocalState ->
{
// Process this job (we're now in one of the processing threads)
TO result = processor.apply( job, threadLocalState );
// Wait until it's my turn to add this result to the result queue, we have to add it in the
// correct order so that we preserve the ticket order. We want to wait as short periods of time
// as possible here because every cycle we wait adding this result, we're also blocking
// other results from being added to the result queue
await( myTurnToAddToProcessedQueue, ticket, healthCheck, park );
// OK now it's my turn to add this result to the result queue which user will pull from later on
while ( !processed.offer( result, 10, MILLISECONDS ) );
// Signal that this ticket has been processed and added to the result queue
processedTicket.incrementAndGet();
} );
}
/**
* Essentially starting a thread {@link #submit(Object) submitting} a stream of inputs which will
* each be processed and asynchronically made available in order of processing ticket by later calling
* {@link #next()}.
*
* @param input {@link Iterator} of input to process.
* @param shutdownAfterAllSubmitted will call {@link #shutdown(boolean)} after all jobs submitted if {@code true}.
* @return {@link Future} representing the work of submitting the inputs to be processed. When the future
* is completed all items from the {@code input} {@link Iterator} have been submitted, but some items
* may still be queued and processed.
*/
public Future<Void> slurp( Iterator<FROM> input, boolean shutdownAfterAllSubmitted )
{
return future( () ->
{
while ( input.hasNext() )
{
submit( input.next() );
}
if ( shutdownAfterAllSubmitted )
{
shutdown( true );
}
return null;
} );
}
/**
* Tells this processor that there will be no more submissions and so {@link #next()} will stop blocking,
* waiting for new processed results.
*
* @param awaitAllProcessed if {@code true} will block until all submitted jobs have been processed,
* otherwise if {@code false} will return immediately, where processing will still commence and complete.
*/
public void shutdown( boolean awaitAllProcessed )
{
done = true;
executor.shutdown( awaitAllProcessed ? TaskExecutor.SF_AWAIT_ALL_COMPLETED : 0 );
}
/**
* @return next processed job (blocking call), or {@code null} if all jobs have been processed
* and {@link #shutdown(boolean)} has been called.
*/
public TO next()
{
while ( !done || processedTicket.get() < submittedTicket.get() || !processed.isEmpty() )
{
try
{
TO next = processed.poll( 10, MILLISECONDS );
if ( next != null )
{
return next;
}
}
catch ( InterruptedException e )
{
// Someone wants us to abort this thing
Thread.currentThread().interrupt();
return null;
}
healthCheck.run();
}
// We've reached the end of the line
return null;
}
@Override
public int processors( int delta )
{
return executor.processors( delta );
}
}