From 6969cacacc63969e65f5ab53dad5c3ffe0147eaa Mon Sep 17 00:00:00 2001
From: Florian Sylvain <sylvainflorian@proton.me>
Date: Wed, 14 May 2025 00:53:24 +0200
Subject: [PATCH] feat: ThreadPool refac & dynamic thread management

---
 src/Game.cpp        | 10 +++++---
 src/ThreadPool.cpp  | 51 ++++++++++++++++++++++++++++++++++++++++
 src/ThreadPool.hpp  | 57 +++++++++++----------------------------------
 src/ThreadUtils.hpp | 10 ++++++++
 4 files changed, 82 insertions(+), 46 deletions(-)
 create mode 100644 src/ThreadPool.cpp

diff --git a/src/Game.cpp b/src/Game.cpp
index 4e7653b..ca78587 100644
--- a/src/Game.cpp
+++ b/src/Game.cpp
@@ -164,10 +164,14 @@ void Game::update() {
 }
 
 void Game::updateBallsParallel(float dt) {
-  const size_t chunkSize =
-      std::max(static_cast<size_t>(1),
-               m_objects.size() / std::thread::hardware_concurrency());
+  const size_t optimalThreads =
+      ThreadUtils::calculateOptimalThreads(m_objects.size());
+  if (m_threadPool.getThreadCount() != optimalThreads) {
+    m_threadPool.resize(optimalThreads);
+  }
 
+  const size_t chunkSize =
+      std::max(static_cast<size_t>(1), m_objects.size() / optimalThreads);
   std::vector<std::future<void>> futures;
 
   for (size_t i = 0; i < m_objects.size(); i += chunkSize) {
diff --git a/src/ThreadPool.cpp b/src/ThreadPool.cpp
new file mode 100644
index 0000000..4e278df
--- /dev/null
+++ b/src/ThreadPool.cpp
@@ -0,0 +1,51 @@
+
+#include "ThreadPool.hpp"
+
+ThreadPool::ThreadPool(const size_t numThreads) : stop(false) {
+  startWorkers(numThreads);
+}
+
+ThreadPool::~ThreadPool() { stopAllWorkers(); }
+
+void ThreadPool::resize(const size_t newSize) {
+  if (newSize == workers.size()) return;
+
+  stopAllWorkers();
+  workers.clear();
+  stop = false;
+  startWorkers(newSize);
+}
+
+void ThreadPool::stopAllWorkers() {
+  {
+    std::unique_lock lock(queueMutex);
+    stop = true;
+  }
+  condition.notify_all();
+  for (auto& worker : workers) {
+    if (worker.joinable()) {
+      worker.join();
+    }
+  }
+}
+
+void ThreadPool::startWorkers(const size_t numWorkers) {
+  for (size_t i = 0; i < numWorkers; ++i) {
+    workers.emplace_back([this] {
+      while (true) {
+        std::function<void()> task;
+        {
+          std::unique_lock lock(this->queueMutex);
+          this->condition.wait(
+              lock, [this] { return this->stop || !this->tasks.empty(); });
+
+          if (this->stop && this->tasks.empty()) return;
+
+          task = std::move(this->tasks.front());
+          this->tasks.pop();
+        }
+        task();
+      }
+    });
+  }
+}
diff --git a/src/ThreadPool.hpp b/src/ThreadPool.hpp
index 0d62eb6..daa4e24 100644
--- a/src/ThreadPool.hpp
+++ b/src/ThreadPool.hpp
@@ -1,3 +1,4 @@
+
 #pragma once
 #include <condition_variable>
 #include <functional>
@@ -10,63 +11,33 @@
 class ThreadPool {
  public:
   explicit ThreadPool(size_t numThreads);
-
   ~ThreadPool();
 
   [[nodiscard]] size_t getThreadCount() const { return workers.size(); }
 
+  void resize(size_t newSize);
+
   template <class F, class... Args>
-  auto enqueue(F &&f, Args &&...args)
-      -> std::future<std::invoke_result_t<F, Args...> >;
+  auto enqueue(F&& f, Args&&... args)
+      -> std::future<std::invoke_result_t<F, Args...>>;
 
  private:
+  void stopAllWorkers();
+  void startWorkers(size_t numWorkers);
+
   std::vector<std::thread> workers;
-
-  std::queue<std::function<void()> > tasks;
-
+  std::queue<std::function<void()>> tasks;
   std::mutex queueMutex;
   std::condition_variable condition;
-  bool stop;
+  bool stop{false};
 };
 
-inline ThreadPool::ThreadPool(const size_t numThreads) : stop(false) {
-  for (size_t i = 0; i < numThreads; ++i) {
-    workers.emplace_back([this] {
-      while (true) {
-        std::function<void()> task;
-        {
-          std::unique_lock lock(this->queueMutex);
-          this->condition.wait(
-              lock, [this] { return this->stop || !this->tasks.empty(); });
-
-          if (this->stop && this->tasks.empty()) return;
-
-          task = std::move(this->tasks.front());
-          this->tasks.pop();
-        }
-
-        task();
-      }
-    });
-  }
-}
-
-inline ThreadPool::~ThreadPool() {
-  {
-    std::unique_lock lock(queueMutex);
-    stop = true;
-  }
-  condition.notify_all();
-
-  for (auto &worker : workers) worker.join();
-}
-
 template <class F, class... Args>
-auto ThreadPool::enqueue(F &&f, Args &&...args)
-    -> std::future<std::invoke_result_t<F, Args...> > {
+auto ThreadPool::enqueue(F&& f, Args&&... args)
+    -> std::future<std::invoke_result_t<F, Args...>> {
   using return_type = std::invoke_result_t<F, Args...>;
 
-  auto task = std::make_shared<std::packaged_task<return_type()> >(
+  auto task = std::make_shared<std::packaged_task<return_type()>>(
       std::bind(std::forward<F>(f), std::forward<Args>(args)...));
 
   std::future<return_type> res = task->get_future();
@@ -79,4 +50,4 @@ auto ThreadPool::enqueue(F &&f, Args &&...args)
 
   condition.notify_one();
   return res;
-}
+}
\ No newline at end of file
diff --git a/src/ThreadUtils.hpp b/src/ThreadUtils.hpp
index cc1722e..1ae5ad4 100644
--- a/src/ThreadUtils.hpp
+++ b/src/ThreadUtils.hpp
@@ -1,3 +1,4 @@
+#pragma once
 #include <thread>
 
 namespace ThreadUtils {
@@ -5,4 +6,13 @@ inline size_t calculateSafeWorkerThreads(const size_t reserve = 2) {
   const size_t total = std::thread::hardware_concurrency();
   return total > reserve ? total - reserve : 1;
 }
+
+inline size_t calculateOptimalThreads(const size_t objectCount,
+                                      const size_t minObjectsPerThread = 100) {
+  const size_t maxThreads = calculateSafeWorkerThreads();
+  const size_t optimalThreads =
+      std::max(static_cast<size_t>(1), objectCount / minObjectsPerThread);
+  return std::min(maxThreads, optimalThreads);
+}
+
 }  // namespace ThreadUtils