"emacs -nw" hangs in a terminal

Ken Brown kbrown@cornell.edu
Fri May 25 20:10:00 GMT 2012


On 5/25/2012 2:49 PM, Ken Brown wrote:
> On 5/25/2012 10:35 AM, Corinna Vinschen wrote:
>> I applied a patch which calls the signal handler after cleanup. The
>> downside is that the signal handler is only called if select is called
>> from the main thread. A better patch would perhaps be to stop all
>> threads, call the signal handler, and restart the threads afterwards,
>> but this is more tricky.
>
> Thanks! That fixes it. I appreciate all your work on this.
>
> I'm in the process now of testing to see if this also fixes an emacs
> crash I've been getting when I build emacs with GSettings support
> (http://cygwin.com/ml/cygwin-xfree/2012-04/msg00048.html).

Here's what I'm now seeing with that build.  If I start emacs and do 
'M-x shell', emacs hangs (but doesn't crash).  Attaching gdb and doing a 
backtrace of all threads, I see that cygwin_select has been called in 
two threads other than the main one:

Thread 8 (Thread 2784.0x19c):
#0  0x7702013d in ntdll!RtlEnableEarlyCriticalSectionEventCreation ()
    from /c/windows/SysWOW64/ntdll.dll
#1  0x7702013d in ntdll!RtlEnableEarlyCriticalSectionEventCreation ()
    from /c/windows/SysWOW64/ntdll.dll
#2  0x74fe0bdd in WaitForMultipleObjectsEx ()
    from /c/windows/syswow64/KERNELBASE.dll
#3  0x00000004 in ?? ()
#4  0x74ed1a2c in KERNEL32!GetVolumePathNamesForVolumeNameA ()
    from /c/windows/syswow64/kernel32.dll
#5  0xff11c868 in ?? ()
#6  0x74ed4208 in KERNEL32!CheckForReadOnlyResource ()
    from /c/windows/syswow64/kernel32.dll
#7  0x00000004 in ?? ()
#8  0x610d0b24 in select_stuff::wait (this=0xff11cba4, readfds=0xff11cb00,
     writefds=0xff11cae0, exceptfds=0xff11cac0, ms=4294967295)
     at 
/ext/build/netrel/src/cygwin-snapshot-20120525-1/winsup/cygwin/select.cc:320
#9  0x610d154b in cygwin_select (maxfds=13, readfds=0xff11cc70,
     writefds=0xff11cc50, exceptfds=0xff11cc30, to=0x0)
     at 
/ext/build/netrel/src/cygwin-snapshot-20120525-1/winsup/cygwin/select.cc:158
#10 0x610b2b5a in poll (fds=0x8012db00, nfds=3, timeout=-1)
     at 
/ext/build/netrel/src/cygwin-snapshot-20120525-1/winsup/cygwin/poll.cc:87
#11 0x610d5575 in _sigfe () from /usr/bin/cygwin1.dll
#12 0xffffffff in ?? ()
#13 0x8012db00 in ?? ()
#14 0x6ac1e759 in g_main_loop_run () from /usr/bin/cygglib-2.0-0.dll
#15 0x6ad96d40 in g_dbus_proxy_call_with_unix_fd_list_sync ()
    from /usr/bin/cyggio-2.0-0.dll
#16 0x6ac401ef in g_thread_proxy () from /usr/bin/cygglib-2.0-0.dll
#17 0x610fca42 in pthread::thread_init_wrapper (arg=0x80130e00)
     at 
/ext/build/netrel/src/cygwin-snapshot-20120525-1/winsup/cygwin/thread.cc:2104
#18 0x61086f62 in thread_wrapper (arg=0x0)
     at 
/ext/build/netrel/src/cygwin-snapshot-20120525-1/winsup/cygwin/miscfuncs.cc:547
#19 0x00000000 in ?? ()

Thread 7 (Thread 2784.0xb4c):
#0  0x7702013d in ntdll!RtlEnableEarlyCriticalSectionEventCreation ()
    from /c/windows/SysWOW64/ntdll.dll
#1  0x7702013d in ntdll!RtlEnableEarlyCriticalSectionEventCreation ()
    from /c/windows/SysWOW64/ntdll.dll
#2  0x74fe0bdd in WaitForMultipleObjectsEx ()
    from /c/windows/syswow64/KERNELBASE.dll
#3  0x00000003 in ?? ()
#4  0x74ed1a2c in KERNEL32!GetVolumePathNamesForVolumeNameA ()
    from /c/windows/syswow64/kernel32.dll
#5  0xff21c858 in ?? ()
#6  0x74ed4208 in KERNEL32!CheckForReadOnlyResource ()
    from /c/windows/syswow64/kernel32.dll
#7  0x00000003 in ?? ()
#8  0x610d0b24 in select_stuff::wait (this=0xff21cb94, readfds=0xff21caf0,
     writefds=0xff21cad0, exceptfds=0xff21cab0, ms=4294967295)
     at 
/ext/build/netrel/src/cygwin-snapshot-20120525-1/winsup/cygwin/select.cc:320
#9  0x610d154b in cygwin_select (maxfds=8, readfds=0xff21cc60,
     writefds=0xff21cc40, exceptfds=0xff21cc20, to=0x0)
     at 
/ext/build/netrel/src/cygwin-snapshot-20120525-1/winsup/cygwin/select.cc:158
#10 0x610b2b5a in poll (fds=0x8009b3c0, nfds=1, timeout=-1)
     at 
/ext/build/netrel/src/cygwin-snapshot-20120525-1/winsup/cygwin/poll.cc:87
#11 0x610d5575 in _sigfe () from /usr/bin/cygwin1.dll
#12 0xffffffff in ?? ()
#13 0x8009b3c0 in ?? ()
#14 0x6ac1e759 in g_main_loop_run () from /usr/bin/cygglib-2.0-0.dll
#15 0x63e32eca in gvdb_table_walk ()
    from /usr/lib/gio/modules/cygdconfsettings.dll
#16 0x6ac401ef in g_thread_proxy () from /usr/bin/cygglib-2.0-0.dll
#17 0x610fca42 in pthread::thread_init_wrapper (arg=0x8009c700)
     at 
/ext/build/netrel/src/cygwin-snapshot-20120525-1/winsup/cygwin/thread.cc:2104
#18 0x61086f62 in thread_wrapper (arg=0x0)
     at 
/ext/build/netrel/src/cygwin-snapshot-20120525-1/winsup/cygwin/miscfuncs.cc:547
#19 0x00000000 in ?? ()

It looks like these threads are being used by GLib, which is running a 
loop that calls poll, which calls cygwin_select.  So maybe the "better 
patch" that you referred to would fix this hang.

Ken

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