guru.nidi.graphviz.model.SafeRecursion Maven / Gradle / Ivy
/*
* Copyright © 2015 Stefan Niederhauser ([email protected])
*
* Licensed 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 "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
package guru.nidi.graphviz.model;
import java.util.*;
import java.util.function.Supplier;
class SafeRecursion {
private final ThreadLocal> targetsHolder = new ThreadLocal<>();
R recurse(T target, R shortcutResult, Supplier action) {
Set targets = targetsHolder.get();
if (targets == null) {
try {
targets = Collections.newSetFromMap(new IdentityHashMap<>());
targetsHolder.set(targets);
targets.add(target);
return action.get();
} finally {
targetsHolder.remove();
}
}
if (targets.contains(target)) {
return shortcutResult;
}
targets.add(target);
return action.get();
}
}