[GStreamer][MSE] Fix hang on clearing/destroying AppendPipeline

[emutavchi]

The deadlock may occur when UI thread tries to clear pipeline in
AppendPipeline::clearPlayerPrivate() while parser thread tries to change
pipeline state to pause holding the stream lock in
AppendPipeline::connectDemuxerSrcPadToAppsinkFromAnyThread()

[emutavchi]

Backtrace of deadlock:

Thread 9 (LWP 18343):
#0  __lll_lock_wait (futex=0x7b5928, private=0) at ../nptl/sysdeps/unix/sysv/linux/lowlevellock.c:45
#1  0x755c4928 in __GI___pthread_mutex_lock (mutex=0x7b5928) at pthread_mutex_lock.c:114
#2  0x7485bc2c in g_rec_mutex_lock (mutex=0x60f500) at /usr/src/debug/glib-2.0/1_2.48.1-r0/glib-2.48.1/glib/gthread-posix.c:386
#3  0x746b04bc in gst_element_set_state_func (element=0x60f4c0, state=GST_STATE_PAUSED) at gstelement.c:2574
#4  0x746af998 in gst_element_set_state (element=0x60f4c0, state=GST_STATE_PAUSED) at gstelement.c:2550
#5  0x76fe3c8c in connectDemuxerSrcPadToAppsinkFromAnyThread ()
    at git/Source/WebCore/platform/graphics/gstreamer/mse/AppendPipeline.cpp:1102
#6  0x73015cb0 in g_cclosure_marshal_VOID__OBJECTv (closure=0x67ac48, return_value=0x0, instance=0x6148d8, args=0x59d9c924, marshal_data=marshal_data@entry=0x0, n_params=n_params@entry=1, 
    param_types=param_types@entry=0x474df0) at /usr/src/debug/glib-2.0/1_2.48.1-r0/glib-2.48.1/gobject/gmarshal.c:2102
#7  0x73011df0 in _g_closure_invoke_va (closure=0x67ac48, return_value=0x0, instance=0x6148d8, args=0x59d9c924, n_params=1, param_types=0x474df0)
    at /usr/src/debug/glib-2.0/1_2.48.1-r0/glib-2.48.1/gobject/gclosure.c:867
#8  0x73036460 in g_signal_emit_valist (instance=0x6148d8, signal_id=<optimized out>, detail=0, var_args=0x59d9c924) at /usr/src/debug/glib-2.0/1_2.48.1-r0/glib-2.48.1/gobject/gsignal.c:3294
#9  0x73036fdc in g_signal_emit (instance=<optimized out>, signal_id=<optimized out>, detail=<optimized out>) at /usr/src/debug/glib-2.0/1_2.48.1-r0/glib-2.48.1/gobject/gsignal.c:3441
#10 0x746aae60 in gst_element_add_pad (element=0x6148d8, pad=0x61b180) at gstelement.c:713
#11 0x5a186f70 in gst_qtdemux_add_stream (list=0x5c019a30, stream=0x71775600, qtdemux=0x6148d8) at qtdemux.c:7799
#12 qtdemux_expose_streams (qtdemux=0x6148d8) at qtdemux.c:11248
#13 0x5a1a9384 in gst_qtdemux_process_adapter (demux=0x6148d8, force=0) at qtdemux.c:6384
#14 0x5a1aae0c in gst_qtdemux_chain (sinkpad=0x61bd50, parent=0x6148d8, inbuf=0x5872c298) at qtdemux.c:6196
#15 0x746d2a08 in gst_pad_chain_data_unchecked (data=0x5872c298, type=4112, pad=0x61bd50) at gstpad.c:4202
#16 gst_pad_push_data (pad=0x62a6b0, type=4112, data=<optimized out>) at gstpad.c:4454
#17 0x746ddcc8 in gst_pad_push (pad=0x62a6b0, buffer=0x5872c298) at gstpad.c:4573
#18 0x7418a964 in gst_base_src_loop (pad=0x62a6b0) at gstbasesrc.c:2854
#19 0x7471d15c in gst_task_func (task=0x5c032f60) at gsttask.c:334
#20 0x7471eaa8 in default_func (tdata=<optimized out>, pool=<optimized out>) at gsttaskpool.c:68
#21 0x74832c40 in g_thread_pool_thread_proxy (data=<optimized out>) at /usr/src/debug/glib-2.0/1_2.48.1-r0/glib-2.48.1/glib/gthreadpool.c:307
#22 0x74831ad0 in g_thread_proxy (data=0x5c0127b0) at /usr/src/debug/glib-2.0/1_2.48.1-r0/glib-2.48.1/glib/gthread.c:780
---Type <return> to continue, or q <return> to quit---
#23 0x755c0cdc in start_thread (arg=0x59d9d360) at pthread_create.c:314
#24 0x753b7a40 in __thread_start () at ../ports/sysdeps/unix/sysv/linux/mips/clone.S:150


Thread 1 (LWP 652):
#0  __lll_lock_wait (futex=0x6eb0b0, private=0) at ../nptl/sysdeps/unix/sysv/linux/lowlevellock.c:45
#1  0x755c4928 in __GI___pthread_mutex_lock (mutex=0x6eb0b0) at pthread_mutex_lock.c:114
#2  0x7485bc2c in g_rec_mutex_lock (mutex=0x61bd9c) at /usr/src/debug/glib-2.0/1_2.48.1-r0/glib-2.48.1/glib/gthread-posix.c:386
#3  0x746d861c in post_activate (new_mode=GST_PAD_MODE_NONE, pad=0x61bd50) at gstpad.c:1014
#4  activate_mode_internal (pad=0x61bd50, parent=0x6148d8, mode=GST_PAD_MODE_PUSH, active=0) at gstpad.c:1185
#5  0x746d8f38 in gst_pad_set_active (pad=0x61bd50, active=0) at gstpad.c:1079
#6  0x746a8e10 in activate_pads (vpad=0x7fcff648, ret=0x7fcff6a0, active=0x7fcff724) at gstelement.c:2783
#7  0x746c2a40 in gst_iterator_fold (it=0x71757ad8, func=0x746a8dbc <activate_pads>, ret=0x7fcff6a0, user_data=0x7fcff724) at gstiterator.c:616
#8  0x746a999c in iterator_activate_fold_with_resync (iter=0x71757ad8, user_data=0x7fcff724, func=0x746a8dbc <activate_pads>) at gstelement.c:2807
#9  0x746ac724 in gst_element_pads_activate (element=0x6148d8, active=0) at gstelement.c:2851
#10 0x746acbb0 in gst_element_change_state_func (element=0x6148d8, transition=<optimized out>) at gstelement.c:2917
#11 0x5a186b24 in gst_qtdemux_change_state (element=0x6148d8, transition=GST_STATE_CHANGE_PAUSED_TO_READY) at qtdemux.c:2473
#12 0x746afdb0 in gst_element_change_state (element=0x6148d8, transition=GST_STATE_CHANGE_PAUSED_TO_READY) at gstelement.c:2695
#13 0x746b07fc in gst_element_set_state_func (element=0x6148d8, state=<optimized out>) at gstelement.c:2649
#14 0x746af998 in gst_element_set_state (element=0x6148d8, state=GST_STATE_READY) at gstelement.c:2550
#15 0x7467cdc4 in gst_bin_element_set_state (next=GST_STATE_READY, current=GST_STATE_PAUSED, start_time=0, base_time=44774882891273, element=0x6148d8, bin=0x60f4c0) at gstbin.c:2619
#16 gst_bin_change_state_func (element=0x60f4c0, transition=GST_STATE_CHANGE_PAUSED_TO_READY) at gstbin.c:2961
#17 0x746e4950 in gst_pipeline_change_state (element=0x60f4c0, transition=GST_STATE_CHANGE_PAUSED_TO_READY) at gstpipeline.c:499
#18 0x746afdb0 in gst_element_change_state (element=0x60f4c0, transition=GST_STATE_CHANGE_PAUSED_TO_READY) at gstelement.c:2695
#19 0x746b07fc in gst_element_set_state_func (element=0x60f4c0, state=<optimized out>) at gstelement.c:2649
#20 0x746af998 in gst_element_set_state (element=0x60f4c0, state=GST_STATE_NULL) at gstelement.c:2550
#21 0x76fdef58 in clearPlayerPrivate ()
    at git/Source/WebCore/platform/graphics/gstreamer/mse/AppendPipeline.cpp:331
#22 0x76d8ca28 in removedFromMediaSource ()
    at git/Source/WebCore/platform/graphics/gstreamer/mse/MediaSourceClientGStreamerMSE.cpp:193
#23 0x76d9149c in removedFromMediaSource ()
    at git/Source/WebCore/platform/graphics/gstreamer/mse/SourceBufferPrivateGStreamer.cpp:96
#24 0x768ecb14 in removedFromMediaSource ()
    at git/Source/WebCore/Modules/mediasource/SourceBuffer.cpp:416
#25 0x768e8690 in removeSourceBuffer ()
    at git/Source/WebCore/Modules/mediasource/MediaSource.cpp:842
#26 0x768e88a8 in detachFromElement ()
    at git/Source/WebCore/Modules/mediasource/MediaSource.cpp:933
#27 0x7656cd54 in detachMediaSource ()
    at git/Source/WebCore/html/HTMLMediaElement.cpp:3281
#28 0x765d0cf4 in prepareForLoad ()
    at git/Source/WebCore/html/HTMLMediaElement.cpp:1185
#29 0x765d5b44 in load () at git/Source/WebCore/html/HTMLMediaElement.cpp:1145
#30 0x7709b020 in jsHTMLMediaElementPrototypeFunctionLoadCaller () at DerivedSources/WebCore/JSHTMLMediaElement.cpp:1595
#31 callOperation<WebCore::jsHTMLMediaElementPrototypeFunctionLoadCaller, (WebCore::CastedThisErrorBehavior)0> ()
    at git/Source/WebCore/bindings/js/JSDOMBinding.h:362
#32 jsHTMLMediaElementPrototypeFunctionLoad () at DerivedSources/WebCore/JSHTMLMediaElement.cpp:1587
warning: GDB can't find the start of the function at 0x599358ff.
#33 0x59935900 in ?? ()

[eocanha]

Thanks a lot for detecting this bug and providing a patch!