From ae94d83f271f52ca47ab11604acbb3a16f1ee5e3 Mon Sep 17 00:00:00 2001
From: Dan Engelbrecht <dan.engelbrecht@epicgames.com>
Date: Mon, 13 Apr 2026 22:45:09 +0200
Subject: let windows threads in thread pools die if inactive trim mimalloc
 pages if thread in thread pool is idle for 2 min (non-windows)

---
 src/zencore/include/zencore/blockingqueue.h | 29 ++++++++++++
 src/zencore/workthreadpool.cpp              | 68 +++++++++++++++--------------
 2 files changed, 64 insertions(+), 33 deletions(-)

(limited to 'src')

diff --git a/src/zencore/include/zencore/blockingqueue.h b/src/zencore/include/zencore/blockingqueue.h
index b6c93e937..076af3aaf 100644
--- a/src/zencore/include/zencore/blockingqueue.h
+++ b/src/zencore/include/zencore/blockingqueue.h
@@ -5,12 +5,20 @@
 #include <zencore/zencore.h>  // For ZEN_ASSERT
 
 #include <atomic>
+#include <chrono>
 #include <condition_variable>
 #include <deque>
 #include <mutex>
 
 namespace zen {
 
+enum class DequeueResult
+{
+	Success,
+	Closed,
+	Timeout,
+};
+
 template<typename T>
 class BlockingQueue
 {
@@ -50,6 +58,27 @@ public:
 		return true;
 	}
 
+	template<typename Rep, typename Period>
+	DequeueResult WaitAndDequeueFor(T& Item, std::chrono::duration<Rep, Period> Timeout)
+	{
+		std::unique_lock Lock(m_Lock);
+		if (m_Queue.empty())
+		{
+			if (m_CompleteAdding)
+			{
+				return DequeueResult::Closed;
+			}
+			m_NewItemSignal.wait_for(Lock, Timeout, [this]() { return !m_Queue.empty() || m_CompleteAdding; });
+			if (m_Queue.empty())
+			{
+				return m_CompleteAdding ? DequeueResult::Closed : DequeueResult::Timeout;
+			}
+		}
+		Item = std::move(m_Queue.front());
+		m_Queue.pop_front();
+		return DequeueResult::Success;
+	}
+
 	void CompleteAdding()
 	{
 		std::unique_lock Lock(m_Lock);
diff --git a/src/zencore/workthreadpool.cpp b/src/zencore/workthreadpool.cpp
index 1cb338c66..ef56cb3a6 100644
--- a/src/zencore/workthreadpool.cpp
+++ b/src/zencore/workthreadpool.cpp
@@ -4,11 +4,14 @@
 
 #include <zencore/blockingqueue.h>
 #include <zencore/except.h>
+#include <zencore/fmtutils.h>
 #include <zencore/logging.h>
+#include <zencore/memory/fmalloc.h>
 #include <zencore/scopeguard.h>
 #include <zencore/string.h>
 #include <zencore/testing.h>
 #include <zencore/thread.h>
+#include <zencore/timer.h>
 #include <zencore/trace.h>
 
 #include <thread>
@@ -72,10 +75,10 @@ struct WorkerThreadPool::Impl
 			ThrowLastError("CreateThreadpool failed");
 		}
 
-		if (!SetThreadpoolThreadMinimum(m_ThreadPool, (DWORD)m_ThreadCount))
-		{
-			ThrowLastError("SetThreadpoolThreadMinimum failed");
-		}
+		//		if (!SetThreadpoolThreadMinimum(m_ThreadPool, (DWORD)m_ThreadCount))
+		//		{
+		//			ThrowLastError("SetThreadpoolThreadMinimum failed");
+		//		}
 		SetThreadpoolThreadMaximum(m_ThreadPool, (DWORD)m_ThreadCount);
 
 		InitializeThreadpoolEnvironment(&m_CallbackEnvironment);
@@ -107,10 +110,6 @@ struct WorkerThreadPool::Impl
 	{
 		if (Mode == WorkerThreadPool::EMode::DisableBacklog)
 		{
-			if (m_FreeWorkerCount <= 0)
-			{
-				return Work;
-			}
 			RwLock::ExclusiveLockScope _(m_QueueLock);
 			const int				   QueuedCount = gsl::narrow<int>(m_WorkQueue.size());
 			if (QueuedCount >= m_FreeWorkerCount)
@@ -234,10 +233,6 @@ struct WorkerThreadPool::Impl
 	{
 		if (Mode == WorkerThreadPool::EMode::DisableBacklog)
 		{
-			if (m_FreeWorkerCount <= 0)
-			{
-				return Work;
-			}
 			const int QueuedCount = gsl::narrow<int>(m_WorkQueue.Size());
 			if (QueuedCount >= m_FreeWorkerCount)
 			{
@@ -256,35 +251,42 @@ WorkerThreadPool::Impl::WorkerThreadFunction(ThreadStartInfo Info)
 
 	Info.Latch->CountDown();
 
+	using namespace std::chrono_literals;
+
 	do
 	{
 		Ref<IWork> Work;
-		if (m_WorkQueue.WaitAndDequeue(Work))
-		{
-			m_FreeWorkerCount--;
-			auto _ = MakeGuard([&]() { m_FreeWorkerCount++; });
 
-			try
-			{
-				ZEN_TRACE_CPU_FLUSH("AsyncWork");
-				Work->Execute();
-				Work = {};
-			}
-			catch (const AssertException& Ex)
-			{
-				Work = {};
-				ZEN_WARN("Assert exception in worker thread: {}", Ex.FullDescription());
-			}
-			catch (const std::exception& e)
-			{
-				Work = {};
-				ZEN_ERROR("Caught exception in worker thread: {}", e.what());
-			}
+		DequeueResult Result = m_WorkQueue.WaitAndDequeueFor(Work, 2min);
+		if (Result == DequeueResult::Timeout)
+		{
+			GMalloc->Trim(false);
+			continue;
 		}
-		else
+		if (Result == DequeueResult::Closed)
 		{
 			return;
 		}
+
+		m_FreeWorkerCount--;
+		auto _ = MakeGuard([&]() { m_FreeWorkerCount++; });
+
+		try
+		{
+			ZEN_TRACE_CPU_FLUSH("AsyncWork");
+			Work->Execute();
+			Work = {};
+		}
+		catch (const AssertException& Ex)
+		{
+			Work = {};
+			ZEN_WARN("Assert exception in worker thread: {}", Ex.FullDescription());
+		}
+		catch (const std::exception& e)
+		{
+			Work = {};
+			ZEN_ERROR("Caught exception in worker thread: {}", e.what());
+		}
 	} while (true);
 }
 
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