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FutureAdapter.java
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FutureAdapter.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.helpers;
import java.util.concurrent.Callable;
import java.util.concurrent.CountDownLatch;
import java.util.concurrent.ExecutionException;
import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;
import java.util.concurrent.Future;
import java.util.concurrent.TimeUnit;
import java.util.concurrent.TimeoutException;
import java.util.function.Supplier;
public abstract class FutureAdapter<V> implements Future<V>
{
@Override
public boolean cancel( boolean mayInterruptIfRunning )
{
throw new UnsupportedOperationException();
}
@Override
public boolean isCancelled()
{
throw new UnsupportedOperationException();
}
public static class Present<V> extends FutureAdapter<V>
{
private final V value;
public Present( V value )
{
this.value = value;
}
@Override
public boolean isDone()
{
return true;
}
@Override
public V get()
{
return value;
}
@Override
public V get( long timeout, TimeUnit unit )
{
return value;
}
}
public static <T> Present<T> present( T value )
{
return new Present<>( value );
}
public static final Future<Void> VOID = new Present<>( null );
public static <T> Future<T> latchGuardedValue( final Supplier<T> supplier, final CountDownLatch guardedByLatch,
final String jobDescription )
{
return new FutureAdapter<T>()
{
@Override
public boolean isDone()
{
return guardedByLatch.getCount() == 0;
}
@Override
public T get() throws InterruptedException, ExecutionException
{
guardedByLatch.await();
return supplier.get();
}
@Override
public T get( long timeout, TimeUnit unit ) throws InterruptedException, ExecutionException,
TimeoutException
{
if ( !guardedByLatch.await( timeout, unit ) )
{
throw new TimeoutException( jobDescription + " didn't complete within " +
timeout + " " + unit );
}
return supplier.get();
}
};
}
public static Future<Integer> processFuture( final Process process )
{
return new FutureAdapter<Integer>()
{
@Override
public boolean isDone()
{
return tryGetExitValue( process ) != null;
}
private Integer tryGetExitValue( final Process process )
{
try
{
return process.exitValue();
}
catch ( IllegalThreadStateException e )
{ // Thrown if this process hasn't exited yet.
return null;
}
}
@Override
public Integer get() throws InterruptedException
{
return process.waitFor();
}
@Override
public Integer get( long timeout, TimeUnit unit ) throws InterruptedException, ExecutionException,
TimeoutException
{
long end = System.currentTimeMillis() + unit.toMillis( timeout );
while ( System.currentTimeMillis() < end )
{
Integer result = tryGetExitValue( process );
if ( result != null )
{
return result;
}
Thread.sleep( 10 );
}
throw new TimeoutException( "Process '" + process + "' didn't exit within " + timeout + " " + unit );
}
};
}
public static <T> Future<T> future( final Callable<T> task )
{
ExecutorService executor = Executors.newSingleThreadExecutor();
Future<T> future = executor.submit( task );
executor.shutdown();
return future;
}
}