gst: fix aravissrc teardown deadlock under incomplete frames

[MrBlenny]

Problem

Setting a pipeline containing aravissrc to NULL can hang indefinitely. It shows up when complete frames stop arriving - high frame rate, GigE packet loss, bandwidth contention from several cameras, or an unplugged camera and gets worse with more cameras / higher frame rate.

Root cause

gst_aravis_create() waits for a buffer while holding GST_OBJECT_LOCK, and the element registers no GstBaseSrc unlock() vmethod, so the base class has no way to interrupt the wait during a state change. When the stream only yields incomplete (non-SUCCESS) buffers, the do { … } while (status != SUCCESS) loop spins on them forever and never releases the lock, so the PAUSED→READY transition deadlocks waiting for the streaming task to pause / for the lock.

Fix

• Add unlock() / unlock_stop() that set/clear an atomic flushing flag.
• create() now takes a ref on the stream and drops GST_OBJECT_LOCK across the buffer wait, polls in short slices (GST_ARAVIS_BUFFER_POLL_SLICE_US) checking the flag and returning GST_FLOW_FLUSHING promptly on unlock.
• The wait is bounded to buffer_timeout_us total; on continuous failure buffers it now returns GST_FLOW_ERROR instead of spinning.
• start() clears the flag so a reused element streams again.

Behaviour changes (intentional)

• Sustained incomplete frames now surface as GST_FLOW_ERROR after buffer_timeout_us rather than an unbounded spin.
• A missing stream at create() time returns GST_FLOW_FLUSHING instead of hitting an ARV_IS_STREAM g_return_val_if_fail CRITICAL + GST_FLOW_ERROR.

Test

New gstreamer test suite (tests/arvgstteardowntest.c): an in-process fake GV camera with a high gvsp-lost-ratio feeds aravissrc ! fakesink; the test asserts set_state(NULL) completes within a bound. It aborts (deadlock) without the fix and passes with it. Built only when the plugin is enabled; excluded from the valgrind setup like the python suite. subdir('gst') now runs before subdir('tests') so the suite can link the plugin.

Note: I built and ran this against 0.9.3-dev in a container - meson test --suite gstreamer fails (SIGABRT) without the fix and passes with it; a normal 25 fps stream still delivers frames with clean EOS.

[EmmanuelP]

Hi,

Thanks for the patch. Not an issue, but did you use AI to cook this one up ?

The regression test is welcome. But it fails for me:

test:         gstreamer - aravis:gst-teardown                                                                           
start time:   15:31:21                                                                                                  
duration:     19.16s                                                                                                    
result:       killed by signal 6 SIGABRT                                                                                
command:      MSAN_OPTIONS=halt_on_error=1:abort_on_error=1:print_summary=1:print_stacktrace=1 UBSAN_OPTIONS=halt_on_error=1:           ->abort_on_error=1:print_summary=1:print_stacktrace=1 LD_LIBRARY_PATH=/home/pacaud/Sources/aravis/build/src:/opt/MVS/lib/64:/opt/MVS/   ->lib/32:/opt/MVS/lib/64:/opt/MVS/lib/32 MESON_TEST_ITERATION=1 GST_PLUGIN_PATH=/home/pacaud/Sources/aravis/build/gst                   ->ASAN_OPTIONS=halt_on_error=1:abort_on_error=1:print_summary=1 MALLOC_PERTURB_=51 /home/pacaud/Sources/aravis/build/tests/arv-gst-     ->teardown-test
----------------------------------- stdout -----------------------------------                                          
TAP version 14                                                                                                          
# random seed: R02Sa7ec2811353a872f4888b1676c32288e                                                                     
# GLib-GIO-DEBUG: _g_io_module_get_default: Found default implementation gvfs (GDaemonVfs) for ‘gio-vfs’                
1..1                                                                                                                    
# Start of gstreamer tests                                                                                              
not ok /gstreamer/teardown-under-packet-loss - ERROR:../tests/arvgstteardowntest.c:77:teardown_under_packet_loss_test: 'torn_down'      ->should be TRUE
Bail out!                                                                                                               
----------------------------------- stderr -----------------------------------                                          
**                                                                                                                      
ERROR:../tests/arvgstteardowntest.c:77:teardown_under_packet_loss_test: 'torn_down' should be TRUE 

While running the test by hand works:

❯ GST_PLUGIN_PATH=./gst/ ./tests/arv-gst-teardown-test
TAP version 14
# random seed: R02S54e1b7b61d88edfc6b13953f4f5322b7
# GLib-GIO-DEBUG: _g_io_module_get_default: Found default implementation gvfs (GDaemonVfs) for ?gio-vfs?
1..1
# Start of gstreamer tests
ok 1 /gstreamer/teardown-under-packet-loss
# slow test /gstreamer/teardown-under-packet-loss executed in 1.05 secs
# End of gstreamer tests

Any idea why ?

[EmmanuelP]

CI pipelines all fail