libvlc_media_player_stop hangs periodically

[xdenser]

I use libvlc to display UDP stream trhough libvlc_video_set_callbacks.
Task of getting size of frame is solved by creating dummy instance of player to render in 10x10 buffer,
I also use libvlc_event_manager_t to call libvlc_video_get_size from every event
when proper proper size is returned i stop and destroy that dummy instance and start new one with native frame size.

Platform is Windows, language is Delphi

Everything works ok, but in 1 case from 20 or 30 it hangs on libvlc_media_player_stop call on that first dummy instance.
I mean I call libvlc_media_player_stop and it never returns .

[Rémi Denis-Courmont]

Make sure your callbacks are not causing a deadlock. Otherwise, it could be a LibVLC bug. In this case, we need a full thread stack trace or we cannot help you.

[xdenser]

Here is how it looks like in Delphi debugger

:7c90e4f4 ntdll.KiFastSystemCallRet
:7c90df3c ntdll.NtWaitForSingleObject + 0xc
:6a5dfb7c libvlccore.vlc_cond_wait + 0x4c
libvlc_ds_sfilter.TlibvlcSrcPin.Create(???,???,$EC10D0)
libvlc_ds_sfilter.TlibvlcSource.Create('udp://@:1234',0)
VideoWin.TGraphHandler.PreopenFile('udp://@:1234',???)
VideoWin.TTimeCtrl.Preopen
VideoWin.TTimeCtrl.Execute
:0042b68b ThreadProc + $37
:004056e2 ThreadWrapper + $2A
:7c80b713 ; C:\SYS\system32\kernel32.dll

I do not understand yet why it does not display other calls between

:6a5dfb7c libvlccore.vlc_cond_wait + 0x4c
and
libvlc_ds_sfilter.TlibvlcSrcPin.Create(???,???,$EC10D0)

when i set compiler to generate stack frames
it looks like

:7c90e4f4 ntdll.KiFastSystemCallRet
:7c90df3c ntdll.NtWaitForSingleObject + 0xc
:6a5dfb7c libvlccore.vlc_cond_wait + 0x4c
libvlc_player.TLibVLC_CustomRenderPlayer.Destroy
libvlc_dummy_player.Tlibvlc_DummyPlayer.Destroy
libvlc_dummy_player.TSizeGetPlayer.Destroy
:00404757 TObject.Free + $B
libvlc_ds_sfilter.TlibvlcSrcPin.Create(???,???,$EBBDD0)
libvlc_ds_sfilter.TlibvlcSource.Create('udp://@:1234',0)
VideoWin.TGraphHandler.PreopenFile('udp://@:1234',???)
VideoWin.TTimeCtrl.Preopen
VideoWin.TTimeCtrl.Execute
:0042b68b ThreadProc + $37
:004056e2 ThreadWrapper + $2A
:7c80b713 ; C:\SYS\system32\kernel32.dll

but still there are missing calls between

:6a5dfb7c libvlccore.vlc_cond_wait + 0x4c
libvlc_player.TLibVLC_CustomRenderPlayer.Destroy

may be this is because libvlc is linked dinamically

for example this is how looks call to

libvlc_player.pas.269: libvlc_media_player_stop(p_mi);
0056B8D2 52 push edx
0056B8D3 A1EC306000 mov eax,[$006030ec]
0056B8D8 8B00 mov eax,[eax]
0056B8DA FFD0 call eax
0056B8DC 59 pop ecx

in disassembler

[Beardless2]

could you post you entire project of Delphi code in here or on a website somewhere so I can try to assist you?

[xdenser]

The project is too big to post

so I have created small one for testing
it just detects frame size of udp stream by timer (every 10 s)

here

[Rémi Denis-Courmont]

The stack is illegible to me. It goes straight from Delphi code to libvlccore without any libvlc call in the middle. You might be missing the libvlc debug symbols.

[xdenser]

What I got using madExcept:

I think I know where is the problem
the program hangs in main thread on vlc_cond_wait
but at the same time in thread $a38 an event is handled
and libvlc_video_get_size called wich locks some mutex
looks like I should not call libvlc_video_get_size when stopping player


here stack traces of all application threads

main thread ($9b0):
7c90df3a +0a ntdll.dll NtWaitForSingleObject
7c8025d5 +85 kernel32.dll WaitForSingleObjectEx
6a5dfb77 +47 libvlccore.dll vlc_cond_wait
6a5d4f67 +37 libvlccore.dll var_DelCallback
6a3092af +2f libvlc.dll libvlc_media_player_stop
004a6962 +12 test_stop.exe libvlc_player 269 +2 TLibVLC_BasePlayer.Stop
004a6a58 +10 test_stop.exe libvlc_player 316 +2 TLibVLC_CustomRenderPlayer.Destroy
004a6cc5 +15 test_stop.exe libvlc_dummy_player 75 +1 Tlibvlc_DummyPlayer.Destroy
004a6de1 +15 test_stop.exe libvlc_dummy_player 115 +1 TSizeGetPlayer.Destroy
004040ec +08 test_stop.exe System 8832 +1 TObject.Free
004a6c41 +75 test_stop.exe libvlc_dummy_player 59 +17 GetVideoSize
004a705a +36 test_stop.exe TestHangU 40 +2 TForm2.Timer1Timer
0047578f +0f test_stop.exe ExtCtrls 2281 +1 TTimer.Timer
00475673 +2b test_stop.exe ExtCtrls 2239 +4 TTimer.WndProc
00467590 +14 test_stop.exe Classes 11583 +8 StdWndProc
7e3696c2 +0a USER32.dll DispatchMessageA
004a0f00 +fc test_stop.exe Forms 8102 +23 TApplication.ProcessMessage
004a0f22 +0a test_stop.exe Forms 8121 +1 TApplication.HandleMessage
004a1233 +b3 test_stop.exe Forms 8219 +20 TApplication.Run
004a8995 +49 test_stop.exe test_stop 18 +4 initialization

thread $348: <priority:15>
7c90df2a +0a ntdll.dll NtWaitForMultipleObjects
7c80956e +00 kernel32.dll WaitForMultipleObjectsEx
7c80a100 +13 kernel32.dll WaitForMultipleObjects
0044ed89 +0d test_stop.exe madExcept CallThreadProcSafe
0044edf3 +37 test_stop.exe madExcept ThreadExceptFrame
>> created by thread $530 at:
72ce328c +00 wdmaud.drv

thread $a08:
7c90df3a +0a ntdll.dll NtWaitForSingleObject
7c8025d5 +85 kernel32.dll WaitForSingleObjectEx
6a5dfb77 +47 libvlccore.dll vlc_cond_wait
77c2a3ad +a6 msvcrt.dll _endthreadex
0044ed89 +0d test_stop.exe madExcept CallThreadProcSafe
0044edf3 +37 test_stop.exe madExcept ThreadExceptFrame
>> created by main thread ($9b0) at:
77c2a43d +62 msvcrt.dll _beginthreadex

thread $a38: <priority:1>
7c90df3a +00a ntdll.dll NtWaitForSingleObject
7c91b226 +087 ntdll.dll RtlpWaitForCriticalSection
7c901041 +041 ntdll.dll RtlEnterCriticalSection
6a5dfcba +07a libvlccore.dll vlc_mutex_lock
6a309f05 +015 libvlc.dll libvlc_get_input_thread
6a30442b +00b libvlc.dll libvlc_video_get_size
004a6843 +01b test_stop.exe libvlc_player 212 +1 TLibVLC_BasePlayer.GetVideoSize
004a6e14 +014 test_stop.exe libvlc_dummy_player 121 +1 TSizeGetPlayer.Event
004a6822 +012 test_stop.exe libvlc_player 207 +1 TLibVLC_BasePlayer.DispatchEvent
004a6247 +00f test_stop.exe libvlc_player 68 +2 lib_vlc_player_event_hdlr
6a3072ff +1bf libvlc.dll libvlc_event_send
6a5d5500 +150 libvlccore.dll var_AddCallback
6a5d5811 +0a1 libvlccore.dll var_SetChecked
77c2a3ad +0a6 msvcrt.dll _endthreadex
0044ed89 +00d test_stop.exe madExcept CallThreadProcSafe
0044edf3 +037 test_stop.exe madExcept ThreadExceptFrame
>> created by main thread ($9b0) at:
77c2a43d +062 msvcrt.dll _beginthreadex

thread $b44:
7c90df3a +0a ntdll.dll NtWaitForSingleObject
7c8025d5 +85 kernel32.dll WaitForSingleObjectEx
6a5dfb77 +47 libvlccore.dll vlc_cond_wait
6a5bb91f +5f libvlccore.dll block_FifoGet
77c2a3ad +a6 msvcrt.dll _endthreadex
0044ed89 +0d test_stop.exe madExcept CallThreadProcSafe
0044edf3 +37 test_stop.exe madExcept ThreadExceptFrame
>> created by thread $a38 at:
77c2a43d +62 msvcrt.dll _beginthreadex

thread $de8: <priority:2>
7c90df3a +0a ntdll.dll NtWaitForSingleObject
7c8025d5 +85 kernel32.dll WaitForSingleObjectEx
6a5dfb77 +47 libvlccore.dll vlc_cond_wait
6a5bb91f +5f libvlccore.dll block_FifoGet
77c2a3ad +a6 msvcrt.dll _endthreadex
0044ed89 +0d test_stop.exe madExcept CallThreadProcSafe
0044edf3 +37 test_stop.exe madExcept ThreadExceptFrame
>> created by thread $a38 at:
77c2a43d +62 msvcrt.dll _beginthreadex

thread $448: <priority:15>
7c90df2a +0a ntdll.dll NtWaitForMultipleObjects
7c80956e +00 kernel32.dll WaitForMultipleObjectsEx
7c80a100 +13 kernel32.dll WaitForMultipleObjects
0044ed89 +0d test_stop.exe madExcept CallThreadProcSafe
0044edf3 +37 test_stop.exe madExcept ThreadExceptFrame
>> created by thread $de8 at:
73eda31f +00 dsound.dll

thread $e28: <priority:15>
7c90df2a +0a ntdll.dll NtWaitForMultipleObjects
7c80956e +00 kernel32.dll WaitForMultipleObjectsEx
7c80a100 +13 kernel32.dll WaitForMultipleObjects
0044ed89 +0d test_stop.exe madExcept CallThreadProcSafe
0044edf3 +37 test_stop.exe madExcept ThreadExceptFrame
>> created by thread $de8 at:
73eda31f +00 dsound.dll

thread $d88: <priority:15>
7c90d1fa +0a ntdll.dll NtDelayExecution
7c8023eb +4b kernel32.dll SleepEx
6a5bb477 +67 libvlccore.dll mwait
77c2a3ad +a6 msvcrt.dll _endthreadex
0044ed89 +0d test_stop.exe madExcept CallThreadProcSafe
0044edf3 +37 test_stop.exe madExcept ThreadExceptFrame
>> created by thread $de8 at:
77c2a43d +62 msvcrt.dll _beginthreadex

thread $c48: <priority:1>
7c90df3a +0a ntdll.dll NtWaitForSingleObject
7c8025d5 +85 kernel32.dll WaitForSingleObjectEx
6a5dfa91 +c1 libvlccore.dll vlc_cond_timedwait
77c2a3ad +a6 msvcrt.dll _endthreadex
0044ed89 +0d test_stop.exe madExcept CallThreadProcSafe
0044edf3 +37 test_stop.exe madExcept ThreadExceptFrame
>> created by thread $b44 at:
77c2a43d +62 msvcrt.dll _beginthreadex

[xdenser]

ok
i do not call libvlc_video_get_size
while in libvlc_media_player_stop
and it works now

[Jean-Baptiste Kempf]

Hmm, you were calling libvlc_video_get_size when stopping???

[xdenser]

yes. it was called from event handler