From 21ca48b9c2f51f37e892538f443544de9f580204 Mon Sep 17 00:00:00 2001
From: Michael Mandl <mandlm@molez.net>
Date: Wed, 20 Mar 2024 16:35:57 +0100
Subject: [PATCH] feat: automatically detect thread count in parallel finder

---
 QVectorSearch/mainwindow.cpp                |  4 +---
 lib_vector_search/include/parallel_finder.h |  3 +--
 lib_vector_search/src/parallel_finder.cpp   | 19 +++++++++++--------
 3 files changed, 13 insertions(+), 13 deletions(-)

diff --git a/QVectorSearch/mainwindow.cpp b/QVectorSearch/mainwindow.cpp
index c44a8d0..8f7cdfa 100644
--- a/QVectorSearch/mainwindow.cpp
+++ b/QVectorSearch/mainwindow.cpp
@@ -10,7 +10,6 @@
 #include "word_list_generator.h"
 
 #include <sstream>
-#include <thread>
 
 MainWindow::MainWindow(QWidget *parent)
     : QMainWindow(parent), ui(new Ui::MainWindow) {
@@ -70,8 +69,7 @@ void MainWindow::createSelectedFinder() {
     finder_ = std::make_unique<LinearFinder>(word_list_);
     break;
   case 1:
-    finder_ = std::make_unique<ParallelFinder>(
-        word_list_, std::thread::hardware_concurrency());
+    finder_ = std::make_unique<ParallelFinder>(word_list_);
     break;
   case 2:
     finder_ = std::make_unique<TreeFinder>(word_list_);
diff --git a/lib_vector_search/include/parallel_finder.h b/lib_vector_search/include/parallel_finder.h
index 7226e0c..ad2d7e0 100644
--- a/lib_vector_search/include/parallel_finder.h
+++ b/lib_vector_search/include/parallel_finder.h
@@ -6,11 +6,10 @@
 
 class ParallelFinder : public Finder {
 private:
-  const size_t thread_count_;
   const std::vector<string> &word_list_;
 
 public:
-  ParallelFinder(const std::vector<string> &word_list, size_t thread_count);
+  ParallelFinder(const std::vector<string> &word_list);
 
   std::forward_list<const std::string *>
   find_prefix(std::string_view search_term) const override;
diff --git a/lib_vector_search/src/parallel_finder.cpp b/lib_vector_search/src/parallel_finder.cpp
index 1ea4676..e4d5459 100644
--- a/lib_vector_search/src/parallel_finder.cpp
+++ b/lib_vector_search/src/parallel_finder.cpp
@@ -5,23 +5,26 @@
 
 using std::mutex, std::thread, std::lock_guard, std::vector, std::forward_list;
 
-ParallelFinder::ParallelFinder(const vector<string> &word_list,
-                               size_t thread_count)
-    : word_list_(word_list), thread_count_(thread_count) {}
+ParallelFinder::ParallelFinder(const vector<string> &word_list)
+    : word_list_(word_list) {}
 
 forward_list<const string *>
 ParallelFinder::find_prefix(string_view search_term) const {
   forward_list<const string *> result;
   mutex result_mutex;
 
+  const auto word_list_size = word_list_.size();
+
+  const size_t thread_count = thread::hardware_concurrency();
+
   vector<thread> threads;
-  for (size_t thread_index = 0; thread_index < thread_count_; ++thread_index) {
+  for (size_t thread_index = 0; thread_index < thread_count; ++thread_index) {
     const size_t first_word_index =
-        thread_index * (word_list_.size() / thread_count_);
+        thread_index * (word_list_size / thread_count);
     const size_t last_word_index =
-        (thread_index == thread_count_ - 1)
-            ? word_list_.size()
-            : (thread_index + 1) * (word_list_.size() / thread_count_);
+        (thread_index == thread_count - 1)
+            ? word_list_size
+            : (thread_index + 1) * (word_list_size / thread_count);
 
     threads.emplace_back(
         [](const vector<string> &word_list, const string_view &search_term,