gf2121 commented on code in PR #14333: URL: https://github.com/apache/lucene/pull/14333#discussion_r2005865922
########## lucene/core/src/java/org/apache/lucene/codecs/lucene90/blocktree/TrieBuilder.java: ########## @@ -0,0 +1,552 @@ +/* + * 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.lucene.codecs.lucene90.blocktree; + +import java.io.IOException; +import java.util.ArrayDeque; +import java.util.Deque; +import java.util.Iterator; +import java.util.LinkedList; +import java.util.List; +import java.util.ListIterator; +import java.util.function.BiConsumer; +import org.apache.lucene.store.DataOutput; +import org.apache.lucene.store.IndexOutput; +import org.apache.lucene.store.RandomAccessInput; +import org.apache.lucene.util.BytesRef; +import org.apache.lucene.util.BytesRefBuilder; + +/** TODO make it a more memory efficient structure */ +class TrieBuilder { + + static final int SIGN_NO_CHILDREN = 0x00; + static final int SIGN_SINGLE_CHILD_WITH_OUTPUT = 0x01; + static final int SIGN_SINGLE_CHILD_WITHOUT_OUTPUT = 0x02; + static final int SIGN_MULTI_CHILDREN = 0x03; + + static final int LEAF_NODE_HAS_TERMS = 1 << 5; + static final int LEAF_NODE_HAS_FLOOR = 1 << 6; + static final long NON_LEAF_NODE_HAS_TERMS = 1L << 1; + static final long NON_LEAF_NODE_HAS_FLOOR = 1L << 0; + + /** + * The output describing the term block the prefix point to. + * + * @param fp describes the on-disk terms block which a trie node points to. + * @param hasTerms A boolean which will be false if this on-disk block consists entirely of + * pointers to child blocks. + * @param floorData A {@link BytesRef} which will be non-null when a large block of terms sharing + * a single trie prefix is split into multiple on-disk blocks. + */ + record Output(long fp, boolean hasTerms, BytesRef floorData) {} + + private enum Status { + BUILDING, + SAVED, + DESTROYED + } + + private static class Node { + + // The utf8 digit that leads to this Node, 0 for root node + private final int label; + // The children listed in order by their utf8 label + private final LinkedList<Node> children; + // The output of this node. + private Output output; + + // Vars used during saving: + + // The file pointer point to where the node saved. -1 means the node has not been saved. + private long fp = -1; + // The iterator whose next() point to the first child has not been saved. + private Iterator<Node> childrenIterator; + + Node(int label, Output output, LinkedList<Node> children) { + this.label = label; + this.output = output; + this.children = children; + } + } + + private Status status = Status.BUILDING; + final Node root = new Node(0, null, new LinkedList<>()); + + static TrieBuilder bytesRefToTrie(BytesRef k, Output v) { + return new TrieBuilder(k, v); + } + + private TrieBuilder(BytesRef k, Output v) { + if (k.length == 0) { + root.output = v; + return; + } + Node parent = root; + for (int i = 0; i < k.length; i++) { + int b = k.bytes[i + k.offset] & 0xFF; + Output output = i == k.length - 1 ? v : null; + Node node = new Node(b, output, new LinkedList<>()); + parent.children.add(node); + parent = node; + } + } + + /** + * Absorb all (K, V) pairs from the given trie into this one. The given trie builder should not + * have key that already exists in this one, otherwise a {@link IllegalArgumentException } will be + * thrown and this trie will get destroyed. + * + * <p>Note: the given trie will be destroyed after absorbing. + */ + void absorb(TrieBuilder trieBuilder) { + if (status != Status.BUILDING || trieBuilder.status != Status.BUILDING) { + throw new IllegalStateException("tries should be unsaved"); + } + // Use a simple stack to avoid recursion. + Deque<Runnable> stack = new ArrayDeque<>(); + stack.add(() -> absorb(this.root, trieBuilder.root, stack)); + while (!stack.isEmpty()) { + stack.pop().run(); + } + trieBuilder.status = Status.DESTROYED; + } + + private void absorb(Node n, Node add, Deque<Runnable> stack) { + assert n.label == add.label; + if (add.output != null) { + if (n.output != null) { + this.status = Status.DESTROYED; + throw new IllegalArgumentException("Duplicated key found in the given trie."); + } + n.output = add.output; + } + ListIterator<Node> iter = n.children.listIterator(); + // TODO we can do more efficient if there is no intersection, block tree always do that Review Comment: As talked another place, this is a O(M+N), so i'd leave a todo to follow up PR. -- This is an automated message from the Apache Git Service. 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