From 61378d6b911d30ef7ec095bcbb25b243ea07673c Mon Sep 17 00:00:00 2001
From: Timo Rothenpieler <timo@rothenpieler.org>
Date: Tue, 16 Sep 2025 00:13:46 +0200
Subject: [PATCH] avfilter/vsrc_gfxcapture: fix possible missed wakeup race in
 capture loop

---
 libavfilter/vsrc_gfxcapture_winrt.cpp | 25 +++++++++++++++----------
 1 file changed, 15 insertions(+), 10 deletions(-)

diff --git a/libavfilter/vsrc_gfxcapture_winrt.cpp b/libavfilter/vsrc_gfxcapture_winrt.cpp
index 6477e56918..0849380b3a 100644
--- a/libavfilter/vsrc_gfxcapture_winrt.cpp
+++ b/libavfilter/vsrc_gfxcapture_winrt.cpp
@@ -123,8 +123,8 @@ struct GfxCaptureContextWgc {
 
     std::mutex frame_arrived_mutex;
     std::condition_variable frame_arrived_cond;
-    std::atomic<bool> window_closed { false };
-    std::atomic<uint64_t> frame_seq { 0 };
+    bool window_closed { false };
+    uint64_t frame_seq { 0 };
 
     SizeInt32 cap_size { 0, 0 };
     RECT client_area_offsets { 0, 0, 0, 0 };
@@ -196,12 +196,18 @@ static HRESULT get_activation_factory(GfxCaptureContextCpp *ctx, PCWSTR clsid, T
  ****************************************************/
 
 static void wgc_frame_arrived_handler(const std::unique_ptr<GfxCaptureContextWgc> &wgctx) {
-    wgctx->frame_seq.fetch_add(1, std::memory_order_release);
+    {
+        std::lock_guard lock(wgctx->frame_arrived_mutex);
+        wgctx->frame_seq += 1;
+    }
     wgctx->frame_arrived_cond.notify_one();
 }
 
 static void wgc_closed_handler(const std::unique_ptr<GfxCaptureContextWgc> &wgctx) {
-    wgctx->window_closed.store(true, std::memory_order_release);
+    {
+        std::lock_guard lock(wgctx->frame_arrived_mutex);
+        wgctx->window_closed = true;
+    }
     wgctx->frame_arrived_cond.notify_one();
 }
 
@@ -1455,23 +1461,22 @@ static int gfxcapture_activate(AVFilterContext *avctx)
     if (!ff_outlink_frame_wanted(outlink))
         return FFERROR_NOT_READY;
 
-    std::unique_lock frame_lock(wgctx->frame_arrived_mutex);
-
     for (;;) {
-        uint64_t last_seq = wgctx->frame_seq.load(std::memory_order_acquire);
+        uint64_t last_seq = wgctx->frame_seq;
 
         int ret = process_frame_if_exists(outlink);
         if (ret != AVERROR(EAGAIN))
             return ret;
 
-        if (wgctx->window_closed.load(std::memory_order_acquire)) {
+        std::unique_lock frame_lock(wgctx->frame_arrived_mutex);
+
+        if (wgctx->window_closed && wgctx->frame_seq == last_seq) {
             ff_outlink_set_status(outlink, AVERROR_EOF, ctx->last_pts - ctx->first_pts + 1);
             break;
         }
 
         if (!wgctx->frame_arrived_cond.wait_for(frame_lock, std::chrono::seconds(1), [&]() {
-            return wgctx->frame_seq.load(std::memory_order_acquire) != last_seq ||
-                   wgctx->window_closed.load(std::memory_order_acquire);
+            return wgctx->frame_seq != last_seq || wgctx->window_closed;
         }))
             break;
     }