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Swirlds is a software platform designed to build fully-distributed applications that harness the power of the cloud without servers. Now you can develop applications with fairness in decision making, speed, trust and reliability, at a fraction of the cost of traditional server-based platforms.
/*
* Copyright (C) 2023-2024 Hedera Hashgraph, LLC
*
* 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 com.swirlds.common.wiring.model.internal.analysis;
import static com.swirlds.logging.legacy.LogMarker.EXCEPTION;
import static com.swirlds.logging.legacy.LogMarker.STARTUP;
import edu.umd.cs.findbugs.annotations.NonNull;
import java.util.ArrayList;
import java.util.Collection;
import java.util.Deque;
import java.util.HashMap;
import java.util.HashSet;
import java.util.LinkedList;
import java.util.List;
import java.util.Map;
import java.util.Set;
import org.apache.logging.log4j.LogManager;
import org.apache.logging.log4j.Logger;
/**
* A utility for finding cyclical back pressure in a wiring model.
*/
public final class CycleFinder {
private static final Logger logger = LogManager.getLogger(CycleFinder.class);
private CycleFinder() {}
/**
* Check for cyclical back pressure in a wiring model.
*
* @param vertices the vertices in the wiring model
* @return true if there is cyclical backpressure
*/
public static boolean checkForCyclicalBackPressure(@NonNull final Collection vertices) {
for (final ModelVertex vertex : vertices) {
if (checkForCycleStartingFromVertex(vertex)) {
return true;
}
}
logger.info(STARTUP.getMarker(), "No cyclical back pressure detected in wiring model.");
return false;
}
/**
* Check for a cycle starting from a vertex.
*
* @param start the vertex to start from
* @return true if there is a cycle
*/
private static boolean checkForCycleStartingFromVertex(@NonNull final ModelVertex start) {
// Perform a depth first traversal of the graph starting from the given vertex.
// Ignore any edge that doesn't apply back pressure.
final Deque stack = new LinkedList<>();
stack.addLast(start);
final Set visited = new HashSet<>();
// Track the parent of each vertex. Useful for tracing the cycle after it's detected.
final Map parents = new HashMap<>();
while (!stack.isEmpty()) {
final ModelVertex parent = stack.removeLast();
for (final ModelEdge childEdge : parent.getOutgoingEdges()) {
if (!childEdge.isInsertionIsBlocking()) {
// Ignore non-blocking edges.
continue;
}
final ModelVertex child = childEdge.getDestination();
if (child.equals(start)) {
// We've found a cycle!
parents.put(child, parent);
logCycle(start, parents);
return true;
}
if (visited.add(child)) {
stack.addLast(child);
parents.put(child, parent);
}
}
}
return false;
}
/**
* Logs a warning message when cyclical back pressure is detected. Is intended to fail standard test validators.
*
* @param start the vertex where the cycle was detected
* @param parents records the parents for the traversal, used to trace the cycle
*/
private static void logCycle(
@NonNull final ModelVertex start, @NonNull final Map parents) {
final StringBuilder sb = new StringBuilder();
sb.append("Cyclical back pressure detected in wiring model. Cycle: ");
// Following parent links will walk the cycle in reverse order.
final List path = new ArrayList<>();
path.add(start);
ModelVertex target = start;
while (!target.equals(start) || path.size() == 1) {
target = parents.get(target);
path.add(target);
}
for (int i = path.size() - 1; i >= 0; i--) {
sb.append(path.get(i).getName());
if (i > 0) {
sb.append(" -> ");
}
}
logger.error(EXCEPTION.getMarker(), sb.toString());
}
}