Fix thread vector growth in dynamic thread pools

Exiting threads now register their ID before returning, and
PruneExitedThreads() joins and removes them on the next scale-up,
preventing unbounded vector growth through repeated scale cycles.

2 files changed, 36 insertions, 2 deletions

diff --git a/src/zenhttp/servers/iothreadpool.cpp b/src/zenhttp/servers/iothreadpool.cpp
index d180f17f8..1053f0b0c 100644
--- a/src/zenhttp/servers/iothreadpool.cpp
+++ b/src/zenhttp/servers/iothreadpool.cpp
@@ -8,6 +8,7 @@
 
 #if ZEN_PLATFORM_WINDOWS
 
+#	include <algorithm>
 #	include <thread>
 
 namespace zen {
@@ -187,10 +188,36 @@ ExplicitIoThreadPool::CancelIo()
 }
 
 void
+ExplicitIoThreadPool::PruneExitedThreads()
+{
+	// Must be called under m_ThreadListLock
+	if (m_ExitedThreadIds.empty())
+	{
+		return;
+	}
+
+	for (auto It = m_Threads.begin(); It != m_Threads.end();)
+	{
+		auto IdIt = std::find(m_ExitedThreadIds.begin(), m_ExitedThreadIds.end(), It->get_id());
+		if (IdIt != m_ExitedThreadIds.end())
+		{
+			It->join();
+			It = m_Threads.erase(It);
+			m_ExitedThreadIds.erase(IdIt);
+		}
+		else
+		{
+			++It;
+		}
+	}
+}
+
+void
 ExplicitIoThreadPool::SpawnWorkerThread()
 {
 	RwLock::ExclusiveLockScope _(m_ThreadListLock);
 
+	PruneExitedThreads();
 	++m_TotalThreads;
 	m_Threads.emplace_back([this] { WorkerThreadMain(); });
 }
@@ -237,6 +264,10 @@ ExplicitIoThreadPool::WorkerThreadMain()
 						ZEN_LOG_DEBUG(ExplicitIoPoolLog(),
 									  "scaling down I/O thread (idle timeout), {} threads remaining",
 									  CurrentTotal - 1);
+						{
+							RwLock::ExclusiveLockScope _(m_ThreadListLock);
+							m_ExitedThreadIds.push_back(std::this_thread::get_id());
+						}
 						return;	 // Thread exits
 					}
 				}
@@ -278,6 +309,7 @@ ExplicitIoThreadPool::WorkerThreadMain()
 				// We already incremented m_TotalThreads, so do the actual spawn
 				{
 					RwLock::ExclusiveLockScope _(m_ThreadListLock);
+					PruneExitedThreads();
 					m_Threads.emplace_back([this] { WorkerThreadMain(); });
 				}
 			}
diff --git a/src/zenhttp/servers/iothreadpool.h b/src/zenhttp/servers/iothreadpool.h
index e2c15ba76..f6bfce450 100644
--- a/src/zenhttp/servers/iothreadpool.h
+++ b/src/zenhttp/servers/iothreadpool.h
@@ -92,6 +92,7 @@ public:
 private:
 	void WorkerThreadMain();
 	void SpawnWorkerThread();
+	void PruneExitedThreads();
 
 	HANDLE m_Iocp = nullptr;
 
@@ -105,8 +106,9 @@ private:
 	std::atomic<int>  m_ActiveCount{0};
 	std::atomic<bool> m_ShuttingDown{false};
 
-	RwLock					 m_ThreadListLock;
-	std::vector<std::thread> m_Threads;
+	RwLock						 m_ThreadListLock;
+	std::vector<std::thread>	 m_Threads;
+	std::vector<std::thread::id> m_ExitedThreadIds;
 };
 
 }  // namespace zen