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The tracer server for Apache Accumulo to listen for, and store, distributed tracing messages.

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/*
 * Licensed to the Apache Software Foundation (ASF) under one or more
 * contributor license agreements.  See the NOTICE file 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 "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 org.apache.accumulo.tracer;

import java.util.ArrayList;
import java.util.HashMap;
import java.util.HashSet;
import java.util.List;
import java.util.Map;
import java.util.Set;

import org.apache.accumulo.tracer.thrift.RemoteSpan;

public class SpanTree {
  final Map> parentChildren = new HashMap<>();
  public final Map nodes = new HashMap<>();
  private final List rootSpans = new ArrayList<>();

  public void addNode(RemoteSpan span) {
    nodes.put(span.spanId, span);
    if (span.getParentIdsSize() == 0) {
      rootSpans.add(span.spanId);
    }
    for (Long parentId : span.getParentIds()) {
      parentChildren.computeIfAbsent(parentId, id -> new ArrayList<>()).add(span.spanId);
    }
  }

  public Set visit(SpanTreeVisitor visitor) {
    Set visited = new HashSet<>();
    if (rootSpans.isEmpty())
      return visited;
    RemoteSpan rootSpan = nodes.get(rootSpans.iterator().next());
    if (rootSpan == null)
      return visited;
    recurse(0, rootSpan, visitor, visited);
    return visited;
  }

  private void recurse(int level, RemoteSpan node, SpanTreeVisitor visitor, Set visited) {
    // improbable case: duplicate spanId in a trace tree: prevent
    // infinite recursion
    if (visited.contains(node.spanId))
      return;
    visited.add(node.spanId);
    List children = new ArrayList<>();
    List childrenIds = parentChildren.get(node.spanId);
    if (childrenIds != null) {
      for (Long childId : childrenIds) {
        RemoteSpan child = nodes.get(childId);
        if (child != null) {
          children.add(child);
        }
      }
    }
    children = TraceDump.sortByStart(children);
    visitor.visit(level, node);
    for (RemoteSpan child : children) {
      recurse(level + 1, child, visitor, visited);
    }
  }
}