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* distributed with this work for additional information
* regarding copyright ownership. The ASF licenses this file
* to you under the Apache License, Version 2.0 (the
* "License"); you may not use this file except in compliance
* with the License. You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing,
* software distributed under the License is distributed on an
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package org.apache.cayenne.access.dbsync;
import org.apache.cayenne.access.DataNode;
import java.sql.SQLException;
/**
* @since 3.0
*/
// Note that this object must be scoped by DataNode. An attempt to share it between nodes will result in ignoring
// schema update for all but one node (see CAY-2125)
public abstract class BaseSchemaUpdateStrategy implements SchemaUpdateStrategy {
protected volatile boolean run;
protected final ThreadLocal<Boolean> threadRunInProgress;
public BaseSchemaUpdateStrategy() {
// this barrier is needed to prevent stack overflow in the same thread
// (getConnection/updateSchema/getConnection/...)
this.threadRunInProgress = new ThreadLocal<>();
}
@Override
public void updateSchema(DataNode dataNode) throws SQLException {
Boolean inProgress = threadRunInProgress.get();
if (!run && (inProgress == null || !inProgress)) {
synchronized (this) {
if (!run) {
try {
threadRunInProgress.set(true);
processSchemaUpdate(dataNode);
run = true;
}
finally {
threadRunInProgress.set(false);
}
}
}
}
}
/**
* @since 3.0
*/
protected abstract void processSchemaUpdate(DataNode dataNode) throws SQLException;
}