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Fix KVSSINK State Transition Deadlock #1113

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merged 5 commits into from
Dec 7, 2023
Merged

Fix KVSSINK State Transition Deadlock #1113

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3fe16b4
Change parent class stat change position
stefankiesz Nov 29, 2023
abea82f
Add failure check
stefankiesz Nov 29, 2023
49776fe
Testing on mac os 13
stefankiesz Nov 30, 2023
a87b283
Revert ci to mac os 12
stefankiesz Dec 5, 2023
745db12
Add comments explaining state transition guidelines
stefankiesz Dec 6, 2023
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29 changes: 26 additions & 3 deletions src/gstreamer/gstkvssink.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -1572,12 +1572,25 @@ init_track_data(GstKvsSink *kvssink) {

static GstStateChangeReturn
gst_kvs_sink_change_state(GstElement *element, GstStateChange transition) {
/*
The below state transition cases are separated into two switch blocks:
one for upward (NULL->READY->PAUSED->PLAYING) transitions and one for
downward (PLAYING->PAUSED->READY->NULL) transitions. It is necessary to transition
an element's parent class state after any of the element's upward transitions but
before any downward transitions. As per GStreamer documentation,
"this is necessary in order to safely handle concurrent access by multiple threads."

https://gstreamer.freedesktop.org/documentation/plugin-development/basics/states.
html?gi-language=c#:~:text=Note%20that%20upwards,destroying%20allocated%20resources.
*/

GstStateChangeReturn ret = GST_STATE_CHANGE_SUCCESS;
GstKvsSink *kvssink = GST_KVS_SINK (element);
auto data = kvssink->data;
string err_msg = "";
ostringstream oss;

// Upward transitions
switch (transition) {
case GST_STATE_CHANGE_NULL_TO_READY:
if(kvssink->log_config_path != NULL) {
Expand Down Expand Up @@ -1609,6 +1622,18 @@ gst_kvs_sink_change_state(GstElement *element, GstStateChange transition) {
case GST_STATE_CHANGE_READY_TO_PAUSED:
gst_collect_pads_start (kvssink->collect);
break;
default:
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break;
}

// Parent class transition
ret = GST_ELEMENT_CLASS (parent_class)->change_state(element, transition);
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if (ret == GST_STATE_CHANGE_FAILURE) {
goto CleanUp;
}

// Downward transitions
switch (transition) {
case GST_STATE_CHANGE_PAUSED_TO_READY:
LOG_INFO("Stopping kvssink for " << kvssink->stream_name);
gst_collect_pads_stop (kvssink->collect);
Expand All @@ -1631,8 +1656,6 @@ gst_kvs_sink_change_state(GstElement *element, GstStateChange transition) {
break;
}

ret = GST_ELEMENT_CLASS (parent_class)->change_state(element, transition);

CleanUp:

if (ret != GST_STATE_CHANGE_SUCCESS) {
Expand Down Expand Up @@ -1665,4 +1688,4 @@ GST_PLUGIN_DEFINE (
"Proprietary",
"GStreamer",
"http://gstreamer.net/"
)
)