GStreamer: remove an element from a pipeline before setState(NULL)

If an element is a part of a pipeline bin, the bin tries to synchronize
its state with its own. Thus, after setting the element state to NULL,
the state can be set back to READY, PAUSE, or PLAYING before it is
removed from the pipeline. This patch first removes an element from
the pipeline and then sets its state to NULL to avoid this race.

Pick-to: 6.2
Change-Id: Ied9cd037fabab19682a53c5ab3d0c7335c58d9c9
Reviewed-by: Lars Knoll <lars.knoll@qt.io>

3 files changed, 16 insertions, 15 deletions

diff --git a/src/multimedia/platform/gstreamer/common/qgstreamervideooutput.cpp b/src/multimedia/platform/gstreamer/common/qgstreamervideooutput.cpp
index 36e0823d8..56cf0a9a4 100644
--- a/src/multimedia/platform/gstreamer/common/qgstreamervideooutput.cpp
+++ b/src/multimedia/platform/gstreamer/common/qgstreamervideooutput.cpp
@@ -95,8 +95,8 @@ void QGstreamerVideoOutput::setVideoSink(QVideoSink *sink)
 
     gstPipeline.beginConfig();
     if (!videoSink.isNull()) {
-        videoSink.setStateSync(GST_STATE_NULL);
         gstVideoOutput.remove(videoSink);
+        videoSink.setStateSync(GST_STATE_NULL);
     }
     videoSink = gstSink;
     gstVideoOutput.add(videoSink);
@@ -104,7 +104,7 @@ void QGstreamerVideoOutput::setVideoSink(QVideoSink *sink)
     videoConvert.link(videoSink);
     GstEvent *event = gst_event_new_reconfigure();
     gst_element_send_event(videoSink.element(), event);
-    videoSink.setState(GST_STATE_PAUSED);
+    videoSink.syncStateWithParent();
 
     doLinkSubtitleStream();
 
@@ -141,8 +141,8 @@ void QGstreamerVideoOutput::linkSubtitleStream(QGstElement src)
 void QGstreamerVideoOutput::doLinkSubtitleStream()
 {
     if (!subtitleSink.isNull()) {
-        subtitleSink.setStateSync(GST_STATE_NULL);
         gstPipeline.remove(subtitleSink);
+        subtitleSink.setStateSync(GST_STATE_NULL);
         subtitleSink = {};
     }
     if (!m_videoSink || subtitleSrc.isNull())
diff --git a/src/multimedia/platform/gstreamer/mediacapture/qgstreamermediacapture.cpp b/src/multimedia/platform/gstreamer/mediacapture/qgstreamermediacapture.cpp
index 6a0f103a4..3c1793b15 100644
--- a/src/multimedia/platform/gstreamer/mediacapture/qgstreamermediacapture.cpp
+++ b/src/multimedia/platform/gstreamer/mediacapture/qgstreamermediacapture.cpp
@@ -119,14 +119,15 @@ void QGstreamerMediaCapture::setCamera(QPlatformCamera *camera)
         unlinkTeeFromPad(gstVideoTee, imageCaptureSink);
 
         auto camera = gstCamera->gstElement();
-        camera.setStateSync(GST_STATE_NULL);
-        gstVideoTee.setStateSync(GST_STATE_NULL);
-        gstVideoOutput->gstElement().setStateSync(GST_STATE_NULL);
 
         gstPipeline.remove(camera);
         gstPipeline.remove(gstVideoTee);
         gstPipeline.remove(gstVideoOutput->gstElement());
 
+        camera.setStateSync(GST_STATE_NULL);
+        gstVideoTee.setStateSync(GST_STATE_NULL);
+        gstVideoOutput->gstElement().setStateSync(GST_STATE_NULL);
+
         gstVideoTee = {};
         gstCamera->setCaptureSession(nullptr);
     }
@@ -168,8 +169,8 @@ void QGstreamerMediaCapture::setImageCapture(QPlatformImageCapture *imageCapture
 
     if (m_imageCapture) {
         unlinkTeeFromPad(gstVideoTee, imageCaptureSink);
-        m_imageCapture->gstElement().setStateSync(GST_STATE_NULL);
         gstPipeline.remove(m_imageCapture->gstElement());
+        m_imageCapture->gstElement().setStateSync(GST_STATE_NULL);
         imageCaptureSink = {};
         m_imageCapture->setCaptureSession(nullptr);
     }
@@ -245,16 +246,16 @@ void QGstreamerMediaCapture::unlinkEncoder()
     if (!encoderVideoCapsFilter.isNull()) {
         encoderVideoCapsFilter.src().unlinkPeer();
         unlinkTeeFromPad(gstVideoTee, encoderVideoCapsFilter.sink());
-        encoderVideoCapsFilter.setStateSync(GST_STATE_NULL);
         gstPipeline.remove(encoderVideoCapsFilter);
+        encoderVideoCapsFilter.setStateSync(GST_STATE_NULL);
         encoderVideoCapsFilter = {};
     }
 
     if (!encoderAudioCapsFilter.isNull()) {
         encoderAudioCapsFilter.src().unlinkPeer();
         unlinkTeeFromPad(gstAudioTee, encoderAudioCapsFilter.sink());
-        encoderAudioCapsFilter.setStateSync(GST_STATE_NULL);
         gstPipeline.remove(encoderAudioCapsFilter);
+        encoderAudioCapsFilter.setStateSync(GST_STATE_NULL);
         encoderAudioCapsFilter = {};
     }
 
@@ -272,14 +273,14 @@ void QGstreamerMediaCapture::setAudioInput(QPlatformAudioInput *input)
 
         if (gstAudioOutput) {
             unlinkTeeFromPad(gstAudioTee, gstAudioOutput->gstElement().staticPad("sink"));
-            gstAudioOutput->gstElement().setStateSync(GST_STATE_NULL);
             gstPipeline.remove(gstAudioOutput->gstElement());
+            gstAudioOutput->gstElement().setStateSync(GST_STATE_NULL);
         }
 
-        gstAudioInput->gstElement().setStateSync(GST_STATE_NULL);
         gstPipeline.remove(gstAudioInput->gstElement());
-        gstAudioTee.setStateSync(GST_STATE_NULL);
         gstPipeline.remove(gstAudioTee);
+        gstAudioInput->gstElement().setStateSync(GST_STATE_NULL);
+        gstAudioTee.setStateSync(GST_STATE_NULL);
         gstAudioTee = {};
     }
 
@@ -317,8 +318,8 @@ void QGstreamerMediaCapture::setAudioOutput(QPlatformAudioOutput *output)
     if (gstAudioOutput && gstAudioInput) {
         // If audio input is set, the output is in the pipeline
         unlinkTeeFromPad(gstAudioTee, gstAudioOutput->gstElement().staticPad("sink"));
-        gstAudioOutput->gstElement().setStateSync(GST_STATE_NULL);
         gstPipeline.remove(gstAudioOutput->gstElement());
+        gstAudioOutput->gstElement().setStateSync(GST_STATE_NULL);
     }
 
     gstAudioOutput = static_cast<QGstreamerAudioOutput *>(output);
diff --git a/src/multimedia/platform/gstreamer/mediacapture/qgstreamermediaencoder.cpp b/src/multimedia/platform/gstreamer/mediacapture/qgstreamermediaencoder.cpp
index 618544d0d..0461b9576 100644
--- a/src/multimedia/platform/gstreamer/mediacapture/qgstreamermediaencoder.cpp
+++ b/src/multimedia/platform/gstreamer/mediacapture/qgstreamermediaencoder.cpp
@@ -390,10 +390,10 @@ void QGstreamerMediaEncoder::finalize()
 
     qCDebug(qLcMediaEncoder) << "finalize";
 
-    gstEncoder.setStateSync(GST_STATE_NULL);
-    gstFileSink.setStateSync(GST_STATE_NULL);
     gstPipeline.remove(gstEncoder);
     gstPipeline.remove(gstFileSink);
+    gstEncoder.setStateSync(GST_STATE_NULL);
+    gstFileSink.setStateSync(GST_STATE_NULL);
     gstFileSink = {};
     gstEncoder = {};
     m_finalizing = false;