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QueryEngineProvider.java
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QueryEngineProvider.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.kernel.impl.query;
import org.neo4j.helpers.Service;
import org.neo4j.kernel.impl.util.Dependencies;
import org.neo4j.kernel.internal.GraphDatabaseAPI;
import static java.lang.String.format;
public abstract class QueryEngineProvider extends Service
{
public QueryEngineProvider( String name )
{
super( name );
}
protected abstract QueryExecutionEngine createEngine( Dependencies deps, GraphDatabaseAPI graphAPI );
public static QueryExecutionEngine initialize( Dependencies deps, GraphDatabaseAPI graphAPI,
Iterable<QueryEngineProvider> providers )
{
QueryEngineProvider provider = null;
for ( QueryEngineProvider candidate : providers )
{
if ( provider == null )
{
provider = candidate;
}
else
{
throw new IllegalStateException( "Too many query engines." );
}
}
if ( provider == null )
{
return noEngine();
}
QueryExecutionEngine engine = provider.createEngine( deps, graphAPI );
return deps.satisfyDependency( engine );
}
public static QueryExecutionEngine noEngine()
{
return NoQueryEngine.INSTANCE;
}
public static QuerySession embeddedSession( TransactionalContext transactionalContext )
{
final Thread thread = Thread.currentThread();
return new QuerySession( transactionalContext )
{
@Override
public String toString()
{
return format( "embedded-session\tthread\t%s", thread.getName() );
}
};
}
}