From 688feb3d88404598f12440a668136e74044391de Mon Sep 17 00:00:00 2001
From: Caesar <82340152+caesarakalaeii@users.noreply.github.com>
Date: Thu, 6 Aug 2026 18:12:47 +0200
Subject: [PATCH] screencopy: fix permanent freeze after running out of buffers
 (#424)

* screencopy: don't renegotiate the stream when out of buffers

pw_stream_dequeue_buffer() returning nothing only means the consumer has not
recycled a buffer yet. Calling updateStreamParam() there does not help, and it
freezes the session.

pw_stream_update_params() re-enters PW_STREAM_STATE_STREAMING synchronously, so
pwStreamStateChange() sees status == FRAME_NONE and calls startFrameCopy(),
which installs a fresh frame callback. Control returns to the out-of-buffers
branch, which queues a timer. That timer later finds the new callback already in
place and aborts with "tried scheduling on already scheduled cb". The branch
then calls frameCallback.reset() and destroys the callback pipewire had just
installed. Whichever of the two wins the race decides whether the session limps
on for another round or is left with no frame callback and nothing queued, so
the stream stays up but never receives another frame.

Renegotiating also reallocated the whole buffer pool on every retry, so one late
buffer snowballed into continuous renegotiation.

Wait for the next frame slot and retry instead.

* screencopy: keep requeueing frames past MAX_RETRIES

Once copyRetries exceeded MAX_RETRIES the out-of-buffers path stopped queueing
the next frame. That ends the session's frame loop for good: no callback is
pending and no timer will fire again, so the client keeps a live stream that
never receives another frame.

A consumer that is slow for eleven consecutive frames is not a reason to end the
capture. Always requeue, and keep the counter only to bound the logging.
---
 src/portals/Screencopy.cpp | 22 ++++++++++++++--------
 1 file changed, 14 insertions(+), 8 deletions(-)

diff --git a/src/portals/Screencopy.cpp b/src/portals/Screencopy.cpp
index 372b62b..cc232e9 100644
--- a/src/portals/Screencopy.cpp
+++ b/src/portals/Screencopy.cpp
@@ -504,11 +504,14 @@ void CScreencopyPortal::SSession::initCallbacks() {
             if (!PSTREAM->currentPWBuffer) {
                 Debug::log(LOG, "[screencopy/pipewire] Out of buffers");
                 sharingData.status = FRAME_NONE;
-                if (sharingData.copyRetries++ < MAX_RETRIES) {
+                // Renegotiating cannot produce a buffer and breaks the session:
+                // pw_stream_update_params() re-enters STREAMING synchronously, so
+                // pwStreamStateChange() calls startFrameCopy() and installs a new frame
+                // callback. The reset() below then destroys it, leaving the session with
+                // no callback and nothing queued.
+                if (sharingData.copyRetries++ < MAX_RETRIES)
                     Debug::log(LOG, "[sc] Retrying screencopy ({}/{})", sharingData.copyRetries, MAX_RETRIES);
-                    g_pPortalManager->m_sPortals.screencopy->m_pPipewire->updateStreamParam(PSTREAM);
-                    g_pPortalManager->m_sPortals.screencopy->queueNextShareFrame(this);
-                }
+                g_pPortalManager->m_sPortals.screencopy->queueNextShareFrame(this);
                 sharingData.frameCallback.reset();
                 return;
             }
@@ -619,11 +622,14 @@ void CScreencopyPortal::SSession::initCallbacks() {
             if (!PSTREAM->currentPWBuffer) {
                 Debug::log(LOG, "[screencopy/pipewire] Out of buffers");
                 sharingData.status = FRAME_NONE;
-                if (sharingData.copyRetries++ < MAX_RETRIES) {
+                // Renegotiating cannot produce a buffer and breaks the session:
+                // pw_stream_update_params() re-enters STREAMING synchronously, so
+                // pwStreamStateChange() calls startFrameCopy() and installs a new frame
+                // callback. The reset() below then destroys it, leaving the session with
+                // no callback and nothing queued.
+                if (sharingData.copyRetries++ < MAX_RETRIES)
                     Debug::log(LOG, "[sc] Retrying screencopy ({}/{})", sharingData.copyRetries, MAX_RETRIES);
-                    g_pPortalManager->m_sPortals.screencopy->m_pPipewire->updateStreamParam(PSTREAM);
-                    g_pPortalManager->m_sPortals.screencopy->queueNextShareFrame(this);
-                }
+                g_pPortalManager->m_sPortals.screencopy->queueNextShareFrame(this);
                 sharingData.windowFrameCallback.reset();
                 return;
             }