vlc hangs after exiting when its stderr is redirected to stdout

[Daniel Hahler]

When redirecting stderr to stdout, vlc hangs for some seconds:

With redirect:
% time vlc --play-and-exit ~/Videos/foo.avi 2>&1 | grep foo
vlc --play-and-exit ~/Videos/foo.avi 2>&1 0.46s user 0.15s system 35% cpu 1.712 total
grep foo 0.00s user 0.00s system 0% cpu 50.937 total

Normal:
% time vlc --play-and-exit ~/Videos/foo.avi | grep foo
VLC media player 1.1.12 The Luggage (revision exported)
Blocked: call to unsetenv("DBUS_ACTIVATION_ADDRESS")
Blocked: call to unsetenv("DBUS_ACTIVATION_BUS_TYPE")
[0x9c0692c] main libvlc: Running vlc with the default interface. Use 'cvlc' to use vlc without interface.
Blocked: call to setlocale(6, "")
Blocked: call to setlocale(6, "")

(process:31781): Gtk-WARNING **: Locale not supported by C library.
 Using the fallback 'C' locale.
Blocked: call to setlocale(6, "")
xdg-screensaver: Window 0x054001c5 does not exist
vlc --play-and-exit ~/Videos/foo.avi 0.44s user 0.14s system 37% cpu 1.548 total
grep foo 0.00s user 0.00s system 0% cpu 1.417 total

I am using this to find out if a file has been played completely (by grepping for "main playlist: end of playlist, exiting").

This used to work as expected (without a timeout of ~50 seconds), but has regressed during the last months (maybe when upgrading to Ubuntu Oneiric).

I have tested a nightly snapshot (1.2.0~~git20111110+r996-0~r47~oneiric1), which has the same problem.

ProblemType: Bug
DistroRelease: Ubuntu 11.10
Package: vlc 1.1.12-2~oneiric1
ProcVersionSignature: Ubuntu 3.0.0-14.23-generic-pae 3.0.9
Uname: Linux 3.0.0-14-generic-pae i686
ApportVersion: 1.23-0ubuntu4
Architecture: i386
Date: Mon Nov 28 19:42:42 2011
EcryptfsInUse: Yes
InstallationMedia: Ubuntu 11.04 "Natty Narwhal" - Release i386 (20110427.1)
SourcePackage: vlc
UpgradeStatus: Upgraded to oneiric on 2011-09-29 (59 days ago)

[Rémi Denis-Courmont (rdenis)]

Manually updating upstream status.

[Rémi Denis-Courmont (rdenis)]

I am not able to reproduce the problem with the provided instructions.

Please interrupt the process while it is stuck and make a threaded backtrace from that.

[Daniel Hahler (blueyed)]

Thanks Rémi for following up.

It looks like the "grep" process is the one blocking/waiting and it tends to wait 0-60 seconds, like there is a timeout of about one minute in grep / I/O handling.

When suspending the command after closing vlc it looks like this:
% vlc --play-and-exit foo.avi 2>&1 | grep foo
^Z
[2] + 17237 done vlc --play-and-exit 2>&1 |
       17238 suspended grep foo

Should I now attach gdb to grep? This looks as follows, but I am missing the debug symbols for grep (where can those be found?):
(gdb) bt
#0 0xb77c9424 in __kernel_vsyscall ()
#1 0xb76d8153 in __read_nocancel () at ../sysdeps/unix/syscall-template.S:82
#2 0x0804cb3d in ?? ()
#3 0x0804e29b in ?? ()
#4 0x0804a88d in ?? ()
#5 0xb76174d3 in __libc_start_main (main=0x8049cf0, argc=2, ubp_av=0xbf9c0564, init=0x8066330,
    fini=0x80663a0, rtld_fini=0xb77d9280 <_dl_fini>, stack_end=0xbf9c055c) at libc-start.c:226
#6 0x0804adf5 in ?? ()

[Rémi Denis-Courmont (rdenis)]

Synching upstream state manually AGAIN. Please stop this.

[Daniel Hahler (blueyed)]

It appears to be a bug with xdg-utils, or at least triggered from there:

Looking at the strace output, there's a sleep process being invoked, which "hangs"/waits in the end:

    15202 0.000070 execve("/bin/sleep", ["sleep", "50"], [/* 71 vars */] <unfinished ...>

This originates from /usr/lib/vlc/plugins/misc/libxdg_screensaver_plugin.so (where it gets cloned/created from).

Use of this plugin/feature can be toggled in VLC using the "disable-screensaver" setting, which I have enabled (appears to be the default).

This comes from screensaver_suspend_loop out of xdg-screensaver from xdg-utils:

    (while [ -f "$screensaver_file" ]; do $*; sleep 50; done) > /dev/null 2> /dev/null &

This background process seems to be blocking, if stderr is being redirected from vlc, and stdout being read by e.g. grep.

I have not investigated how this worked previously, but it must have changed somehow.

Is there a way to make the "vlc pipeline" end before the subprocess ends itself?

[Launchpad Janitor (janitor)]

Status changed to 'Confirmed' because the bug affects multiple users.