[Octave-bug-tracker] [bug #54607] Native open/save file dialogs have poor performance in KDE

[Stefan Brüns]

Follow-up Comment #54, bug #54607 (project octave):

The cause of the issue becomes quite obvious when using strace ('strace -tf
-etrace=%signal,%process octave --gui')


[pid  3329] 14:36:53 rt_sigaction(SIGPIPE, {sa_handler=SIG_IGN, sa_mask=[],
sa_flags=SA_RESTORER, sa_restorer=0x7f43fde40030}, NULL, 8) = 0
[pid  3329] 14:36:53 kill(3351, SIGTERM) = 0
[pid  3329] 14:36:57 rt_sigaction(SIGCHLD, {sa_handler=0x7f43fa87efc0,
sa_mask=[], sa_flags=SA_RESTORER|SA_SIGINFO|SA_NOCLDSTOP,
sa_restorer=0x7f43fde40030}, {sa_handler=0x7f43fcebfbb0, sa_mask=[],
sa_flags=SA_RESTORER|SA_RESTART, sa_restorer=0x7f43fde40030}, 8) = 0
[pid  3329] 14:36:57 rt_sigaction(SIGPIPE, {sa_handler=SIG_IGN, sa_mask=[],
sa_flags=SA_RESTORER, sa_restorer=0x7f43fde40030}, NULL, 8) = 0
[pid  3330] 14:36:57 exit(0 <unfinished ...>
[pid  3331] 14:36:57 exit(0 <unfinished ...>
[pid  3330] 14:36:57 <... exit resumed>) = ?
[pid  3331] 14:36:57 <... exit resumed>) = ?
[pid  3330] 14:36:57 +++ exited with 0 +++
[pid  3331] 14:36:57 +++ exited with 0 +++
[pid  3333] 14:36:57 exit(0)            = ?
[pid  3333] 14:36:57 +++ exited with 0 +++
[pid  3334] 14:36:57 exit(0)            = ?
[pid  3334] 14:36:57 +++ exited with 0 +++
[pid  3335] 14:36:57 exit(0)            = ?
[pid  3335] 14:36:57 +++ exited with 0 +++
[pid  3336] 14:36:57 exit(0)            = ?
[pid  3336] 14:36:57 +++ exited with 0 +++
[pid  3337] 14:36:57 exit(0)            = ?
[pid  3337] 14:36:57 +++ exited with 0 +++
[pid  3329] 14:36:57 clone(child_stack=NULL,
flags=CLONE_CHILD_CLEARTID|CLONE_CHILD_SETTID|SIGCHLDstrace: Process 3356
attached
, child_tidptr=0x7f43f537cdd0) = 3356
[pid  3356] 14:36:57 rt_sigaction(SIGPIPE, {sa_handler=SIG_DFL,
sa_mask=[PIPE], sa_flags=SA_RESTORER|SA_RESTART, sa_restorer=0x7f43fde40030},
{sa_handler=SIG_IGN, sa_mask=[], sa_flags=SA_RESTORER,
sa_restorer=0x7f43fde40030}, 8) = 0
[pid  3356] 14:36:57 execve("/usr/bin/testparm", ["/usr/bin/testparm", "-d0",
"-s", "--parameter-name", "usershare path"], 0x7f43ac1b7c40 /* 106 vars */) =
0
[pid  3356] 14:36:57 arch_prctl(ARCH_SET_FS, 0x7fb2f255b900) = 0
[pid  3356] 14:36:57 rt_sigaction(SIGRTMIN, {sa_handler=0x7fb2f36dc6b0,
sa_mask=[], sa_flags=SA_RESTORER|SA_SIGINFO, sa_restorer=0x7fb2f36e92d0},
NULL, 8) = 0
[pid  3356] 14:36:57 rt_sigaction(SIGRT_1, {sa_handler=0x7fb2f36dc750,
sa_mask=[], sa_flags=SA_RESTORER|SA_RESTART|SA_SIGINFO,
sa_restorer=0x7fb2f36e92d0}, NULL, 8) = 0
[pid  3356] 14:36:57 rt_sigprocmask(SIG_UNBLOCK, [RTMIN RT_1], NULL, 8) = 0
[pid  3356] 14:36:57 exit_group(0)      = ?
[pid  3356] 14:36:57 +++ exited with 0 +++
[pid  3347] 14:36:57 <... rt_sigtimedwait resumed>{si_signo=SIGCHLD,
si_code=CLD_EXITED, si_pid=3356, si_uid=1000, si_status=0, si_utime=1,
si_stime=0}, NULL, 8) = 17 (SIGCHLD)
[pid  3347] 14:36:57 rt_sigtimedwait([HUP INT QUIT PIPE ALRM TERM CHLD XCPU
XFSZ VTALRM],  <unfinished ...>
[pid  3329] 14:37:27 kill(3356, SIGKILL) = 0
[pid  3329] 14:37:57 clone(child_stack=NULL,
flags=CLONE_CHILD_CLEARTID|CLONE_CHILD_SETTID|SIGCHLDstrace: Process 3395
attached
, child_tidptr=0x7f43f537cdd0) = 3395
[pid  3395] 14:37:57 rt_sigaction(SIGPIPE, {sa_handler=SIG_DFL,
sa_mask=[PIPE], sa_flags=SA_RESTORER|SA_RESTART, sa_restorer=0x7f43fde40030},
{sa_handler=SIG_IGN, sa_mask=[], sa_flags=SA_RESTORER,
sa_restorer=0x7f43fde40030}, 8) = 0
[pid  3395] 14:37:57 execve("/usr/bin/net", ["/usr/bin/net", "usershare",
"info"], 0x7f43ac1b7c40 /* 106 vars */) = 0
[pid  3395] 14:37:57 arch_prctl(ARCH_SET_FS, 0x7f4ee2795440) = 0
[pid  3395] 14:37:57 rt_sigaction(SIGRTMIN, {sa_handler=0x7f4ee39826b0,
sa_mask=[], sa_flags=SA_RESTORER|SA_SIGINFO, sa_restorer=0x7f4ee398f2d0},
NULL, 8) = 0
[pid  3395] 14:37:57 rt_sigaction(SIGRT_1, {sa_handler=0x7f4ee3982750,
sa_mask=[], sa_flags=SA_RESTORER|SA_RESTART|SA_SIGINFO,
sa_restorer=0x7f4ee398f2d0}, NULL, 8) = 0
[pid  3395] 14:37:57 rt_sigprocmask(SIG_UNBLOCK, [RTMIN RT_1], NULL, 8) = 0
[pid  3395] 14:37:57 exit_group(0)      = ?
[pid  3395] 14:37:57 +++ exited with 0 +++
[pid  3347] 14:37:57 <... rt_sigtimedwait resumed>{si_signo=SIGCHLD,
si_code=CLD_EXITED, si_pid=3395, si_uid=1000, si_status=0, si_utime=3,
si_stime=1}, NULL, 8) = 17 (SIGCHLD)
[pid  3347] 14:37:57 rt_sigtimedwait([HUP INT QUIT PIPE ALRM TERM CHLD XCPU
XFSZ VTALRM],  <unfinished ...>
[pid  3329] 14:38:27 kill(3395, SIGKILL) = 0


1. testparm is spawned
2. 30s timeout
3. 30s kill timeout
4. net is spawned
5. 30s timeout
6. 30s kill timeout

The processes are spawned by KDE the KIO SAMBA integration:
https://cgit.kde.org/kio.git/tree/src/core/ksambashare.cpp#n124

QProcess::waitForFinished() never gets the SIGCHLD signal as it is stolen by
sigwait (rt_sigtimedwait([... CHLD ...]).

This is a well known problem, see e.g.
https://bugreports.qt.io/browse/QTBUG-56338

Octave is actually using two handlers for SIGCHLD, once via sigaction from the
main thread, and once via sigwait from the interrupt watcher thread. 

Even without QProcess coming into play the signal handling is indeterminate,
as each signal may be delivered either to the dedicated thread or to the main
thread.

As far as I can see, the fix is trivial - just disabling the signal watcher
thread solves the problem.

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