From 458797a7a726d6f30be2acaea1761d489c31061a Mon Sep 17 00:00:00 2001
From: Nicolas James <nj3ahxac@gmail.com>
Date: Mon, 13 Apr 2026 13:56:11 +1000
Subject: LowLatency2: Avoid fast path when monitor is working

---
 src/strategies/low_latency2/swapchain_monitor.cc | 3 +++
 src/strategies/low_latency2/swapchain_monitor.hh | 2 ++
 2 files changed, 5 insertions(+)

(limited to 'src')

diff --git a/src/strategies/low_latency2/swapchain_monitor.cc b/src/strategies/low_latency2/swapchain_monitor.cc
index 0dcd1ce..088e9bd 100644
--- a/src/strategies/low_latency2/swapchain_monitor.cc
+++ b/src/strategies/low_latency2/swapchain_monitor.cc
@@ -45,6 +45,7 @@ void SwapchainMonitor::do_monitor(const std::stop_token stoken) {
         // Grab mutex protected present delay before we sleep - doesn't matter
         // if it's 'old'.
         const auto delay = this->present_delay;
+        this->is_monitor_processing.store(true, std::memory_order_relaxed);
         lock.unlock();
 
         // Wait for work to complete.
@@ -62,6 +63,7 @@ void SwapchainMonitor::do_monitor(const std::stop_token stoken) {
         }
 
         this->last_signal_time.set(std::chrono::steady_clock::now());
+        this->is_monitor_processing.store(false, std::memory_order_relaxed);
         pending_signal.semaphore_signal.signal(this->device);
     }
 }
@@ -81,6 +83,7 @@ void SwapchainMonitor::notify_semaphore(
     // we have no outstanding work.
     using namespace std::chrono;
     if (this->present_delay == 0us &&
+        !this->is_monitor_processing.load(std::memory_order_relaxed) &&
         std::ranges::all_of(this->pending_frame_spans,
                             [](const auto& frame_span) {
                                 if (!frame_span) {
diff --git a/src/strategies/low_latency2/swapchain_monitor.hh b/src/strategies/low_latency2/swapchain_monitor.hh
index 5906ad1..211da4b 100644
--- a/src/strategies/low_latency2/swapchain_monitor.hh
+++ b/src/strategies/low_latency2/swapchain_monitor.hh
@@ -8,6 +8,7 @@
 
 #include <vulkan/vulkan.h>
 
+#include <atomic>
 #include <chrono>
 #include <condition_variable>
 #include <memory>
@@ -34,6 +35,7 @@ class SwapchainMonitor final {
     std::mutex mutex{};
     std::chrono::microseconds present_delay{};
     bool was_low_latency_requested{};
+    std::atomic<bool> is_monitor_processing{};
     AtomicTimePoint last_signal_time{};
 
     std::condition_variable_any cv{};
-- 
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