docs: describe BucketFinder

lib_vector_search/include/bucket_finder.h

@@ -10,17 +10,34 @@ private:
   std::unordered_map<char, WordRefList> directory_;
 
 public:
+  /// Inserts references to all words from word_list between first_index and
+  /// last_index, including first_index, excluding last_index.
   void insert(const WordList &word_list, size_t first_index, size_t last_index);
 
+  /// Find all words that start with search_term
+  /// @return A list with references to the results.
   WordRefList find_prefix(std::string_view search_term) const;
 };
 
+/** This class provides efficient, parallel search over a list of strings.
+ *
+ * References to all input strings are stored in a tree-like structure that
+ * provides fast and lock-free parallel insertion and parallel (with minimal
+ * synchronization) search for all words that start with a given term.
+ */
 class BucketFinder : public Finder {
 private:
   std::vector<Bucket> buckets_;
 
 public:
+  /// Creates a BucketFinder over all words in word_list.
   BucketFinder(const WordList &word_list);
 
+  /// Find all words that start with search_term
+  /// @return A list with references to the results.
   WordRefList find_prefix(std::string_view search_term) const override;
+
+private:
+  /// Inserts references to all words from word_list.
+  void insert(const WordList &word_list);
 };

lib_vector_search/include/word_list.h

@@ -1,12 +1,9 @@
 #pragma once
 
 #include <filesystem>
-#include <mutex>
 #include <string>
 #include <vector>
 
-class WordRefList;
-
 class WordList : public std::vector<std::string> {
 public:
   WordList &multiply(size_t factor);
@@ -15,22 +12,10 @@ public:
   static WordList oneCap();
   static WordList fourCaps();
   static WordList fromFile(const std::filesystem::path &path);
-
-  static void find_prefix_in_range(const WordList &word_list,
-                                   const std::string_view &search_prefix,
-                                   size_t start_index, size_t end_index,
-                                   WordRefList &result,
-                                   std::mutex &result_mutex);
 };
 
 class WordRefList : public std::vector<const std::string *> {
 public:
   WordRefList() = default;
   WordRefList(const WordList &source);
-
-  static void find_prefix_in_range(const WordRefList &word_list,
-                                   const std::string_view &search_prefix,
-                                   size_t start_index, size_t end_index,
-                                   WordRefList &result,
-                                   std::mutex &result_mutex);
 };

lib_vector_search/src/bucket_finder.cpp

@@ -1,8 +1,11 @@
 #include "bucket_finder.h"
 
+#include <algorithm>
+#include <iterator>
 #include <mutex>
-#include <strings.h>
+#include <string>
 #include <thread>
+#include <vector>
 
 void Bucket::insert(const WordList &word_list, size_t first_index,
                     size_t last_index) {
@@ -28,34 +31,35 @@ WordRefList Bucket::find_prefix(std::string_view search_term) const {
   return result;
 }
 
-BucketFinder::BucketFinder(const WordList &word_list) {
+BucketFinder::BucketFinder(const WordList &word_list) { insert(word_list); }
+
+void BucketFinder::insert(const WordList &word_list) {
   if (word_list.empty()) {
     return;
   }
 
+  const size_t max_threads = std::thread::hardware_concurrency();
   const size_t word_list_size = word_list.size();
-  const size_t bucket_count =
+  const size_t bucket_count = std::min<size_t>(max_threads, word_list_size);
-      std::min<size_t>(std::thread::hardware_concurrency(), word_list_size);
   const size_t bucket_size = word_list_size / bucket_count;
 
   buckets_.resize(bucket_count);
 
-  std::vector<std::thread> threads;
+  std::vector<std::thread> insert_threads;
   for (auto bucket_index = 0; bucket_index < bucket_count; ++bucket_index) {
     auto &bucket = buckets_[bucket_index];
 
-    bool is_last_bucket = bucket_index == bucket_count - 1;
+    const bool is_last_bucket = bucket_index == bucket_count - 1;
+    const size_t first_word_index = bucket_index * bucket_size;
+    const size_t last_word_index =
+        is_last_bucket ? word_list_size : first_word_index + bucket_size;
 
-    const size_t first_index = bucket_index * bucket_size;
+    insert_threads.emplace_back([&, first_word_index, last_word_index] {
-    const size_t last_index =
+      bucket.insert(word_list, first_word_index, last_word_index);
-        is_last_bucket ? word_list_size : first_index + bucket_size;
-
-    threads.emplace_back([&, first_index, last_index] {
-      bucket.insert(word_list, first_index, last_index);
     });
   }
 
-  for (auto &thread : threads) {
+  for (auto &thread : insert_threads) {
     thread.join();
   }
 }
@@ -69,7 +73,7 @@ WordRefList BucketFinder::find_prefix(std::string_view search_term) const {
     threads.emplace_back([&] {
       auto thread_search_results = bucket.find_prefix(search_term);
       if (!thread_search_results.empty()) {
-        std::lock_guard result_lock(search_results_mutex);
+        const std::lock_guard result_lock(search_results_mutex);
         std::move(thread_search_results.begin(), thread_search_results.end(),
                   std::back_inserter(search_results));
       }

lib_vector_search/src/grouped_finder.cpp

@@ -19,31 +19,43 @@ WordRefList GroupedFinder::find_prefix(string_view search_prefix) const {
   }
 
   const auto word_list = group->second;
-  const auto word_list_size = word_list.size();
+  const size_t word_list_size = word_list.size();
-
+  const size_t thread_count =
-  const auto thread_count =
       std::min<size_t>(std::thread::hardware_concurrency(), word_list_size);
+  const size_t words_per_thread = word_list_size / thread_count;
 
-  WordRefList result;
+  WordRefList search_results;
-  mutex result_mutex;
+  mutex search_results_mutex;
 
   vector<thread> search_threads;
   for (size_t thread_index = 0; thread_index < thread_count; ++thread_index) {
-    const size_t first_index = thread_index * (word_list_size / thread_count);
+    const bool is_last_thread = thread_index == thread_count - 1;
+    const size_t start_index = thread_index * words_per_thread;
+    const size_t end_index =
+        is_last_thread ? word_list_size : start_index + words_per_thread;
 
-    const size_t last_index =
+    search_threads.emplace_back([&, start_index, end_index] {
-        (thread_index == thread_count - 1)
+      WordRefList local_results;
-            ? word_list_size
-            : (thread_index + 1) * (word_list_size / thread_count);
 
-    search_threads.emplace_back(
+      for (size_t word_index = start_index; word_index < end_index;
-        WordRefList::find_prefix_in_range, cref(word_list), cref(search_prefix),
+           ++word_index) {
-        first_index, last_index, ref(result), ref(result_mutex));
+        const auto *current_word = word_list[word_index];
+        if (current_word->starts_with(search_prefix)) {
+          local_results.push_back(current_word);
+        }
+      }
+
+      if (!local_results.empty()) {
+        const std::lock_guard lock(search_results_mutex);
+        std::move(local_results.begin(), local_results.end(),
+                  std::back_inserter(search_results));
+      }
+    });
   }
 
   for (auto &thread : search_threads) {
     thread.join();
   }
 
-  return result;
+  return search_results;
 }

lib_vector_search/src/parallel_finder.cpp

@@ -9,30 +9,43 @@ ParallelFinder::ParallelFinder(const WordList &word_list)
     : word_list_(word_list) {}
 
 WordRefList ParallelFinder::find_prefix(string_view search_prefix) const {
-  WordRefList result;
+  WordRefList search_results;
-  mutex result_mutex;
+  mutex search_results_mutex;
 
   const size_t word_list_size = word_list_.size();
   const size_t thread_count =
       std::min<size_t>(thread::hardware_concurrency(), word_list_size);
+  const size_t words_per_thread = word_list_size / thread_count;
 
   vector<thread> search_threads;
   for (size_t thread_index = 0; thread_index < thread_count; ++thread_index) {
-    const size_t first_index = thread_index * (word_list_size / thread_count);
+    const bool is_last_thread = thread_index == thread_count - 1;
+    const size_t start_index = thread_index * words_per_thread;
+    const size_t end_index =
+        is_last_thread ? word_list_size : start_index + words_per_thread;
 
-    const size_t last_index =
+    search_threads.emplace_back([&, start_index, end_index] {
-        (thread_index == thread_count - 1)
+      WordRefList local_results;
-            ? word_list_size
-            : (thread_index + 1) * (word_list_size / thread_count);
 
-    search_threads.emplace_back(
+      for (size_t word_index = start_index; word_index < end_index;
-        WordList::find_prefix_in_range, cref(word_list_), cref(search_prefix),
+           ++word_index) {
-        first_index, last_index, ref(result), ref(result_mutex));
+        const auto &current_word = word_list_[word_index];
+        if (current_word.starts_with(search_prefix)) {
+          local_results.push_back(&current_word);
+        }
+      }
+
+      if (!local_results.empty()) {
+        const std::lock_guard lock(search_results_mutex);
+        std::move(local_results.begin(), local_results.end(),
+                  std::back_inserter(search_results));
+      }
+    });
   }
 
   for (auto &thread : search_threads) {
     thread.join();
   }
 
-  return result;
+  return search_results;
 }

lib_vector_search/src/word_list.cpp

@@ -71,50 +71,8 @@ WordList WordList::fromFile(const std::filesystem::path &path) {
   return word_list;
 }
 
-void WordList::find_prefix_in_range(const WordList &word_list,
-                                    const std::string_view &search_prefix,
-                                    size_t start_index, size_t end_index,
-                                    WordRefList &result,
-                                    std::mutex &result_mutex) {
-  WordRefList local_results;
-
-  for (size_t index = start_index; index < end_index; ++index) {
-    const auto &current_word = word_list[index];
-    if (current_word.starts_with(search_prefix)) {
-      local_results.push_back(&current_word);
-    }
-  }
-
-  if (!local_results.empty()) {
-    const std::lock_guard<std::mutex> lock(result_mutex);
-    std::move(local_results.begin(), local_results.end(),
-              std::back_inserter(result));
-  }
-};
-
 WordRefList::WordRefList(const WordList &source) {
   for (const auto &word : source) {
     push_back(&word);
   }
 }
-
-void WordRefList::find_prefix_in_range(const WordRefList &word_list,
-                                       const std::string_view &search_prefix,
-                                       size_t start_index, size_t end_index,
-                                       WordRefList &result,
-                                       std::mutex &result_mutex) {
-  WordRefList local_results;
-
-  for (size_t index = start_index; index < end_index; ++index) {
-    const auto *current_word = word_list[index];
-    if (current_word->starts_with(search_prefix)) {
-      local_results.push_back(current_word);
-    }
-  }
-
-  if (!local_results.empty()) {
-    const std::lock_guard<std::mutex> lock(result_mutex);
-    std::move(local_results.begin(), local_results.end(),
-              std::back_inserter(result));
-  }
-};