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LockWaitStrategies.java
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LockWaitStrategies.java
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/*
* Copyright (c) 2002-2018 "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.kernel.impl.util.concurrent;
import org.neo4j.storageengine.api.lock.AcquireLockTimeoutException;
import org.neo4j.storageengine.api.lock.WaitStrategy;
import static org.neo4j.kernel.api.exceptions.Status.Transaction.Interrupted;
public enum LockWaitStrategies implements WaitStrategy<AcquireLockTimeoutException>
{
SPIN
{
@Override
public void apply( long iteration ) throws AcquireLockTimeoutException
{
// TODO We can experiment with introducing branch mispredictions here, to create
// TODO bubbles in the pipeline that'll allow hyper-threaded threads on the
// TODO same core to make progress. We can do that by generating a random number,
// TODO e.g. with XorShift, and based on that, randomly branch to do a volatile
// TODO write to one of two fields. The volatile fields would be there to give
// TODO side-effect to the operation, preventing dead-code elimination.
}
},
YIELD
{
@Override
public void apply( long iteration ) throws AcquireLockTimeoutException
{
Thread.yield();
}
},
INCREMENTAL_BACKOFF
{
private static final int spinIterations = 1000;
private static final long multiplyUntilIteration = spinIterations + 2;
@Override
public void apply( long iteration ) throws AcquireLockTimeoutException
{
if ( iteration < spinIterations )
{
SPIN.apply( iteration );
return;
}
try
{
if ( iteration < multiplyUntilIteration )
{
Thread.sleep( 0, 1 << (iteration - spinIterations) );
}
else
{
Thread.sleep( 0, 500 );
}
}
catch ( InterruptedException e )
{
Thread.interrupted();
throw new AcquireLockTimeoutException( e, "Interrupted while waiting.", Interrupted );
}
}
}
}