[PATCH 00/21] FIFO: Support multiple readers

Takashi Yano takashi.yano@nifty.ne.jp
Tue May 19 01:26:09 GMT 2020


Hi Ken,

On Mon, 18 May 2020 13:42:19 -0400
Ken Brown via Cygwin-patches <cygwin-patches@cygwin.com> wrote:
> Hi Takashi,
> 
> On 5/18/2020 12:03 PM, Ken Brown via Cygwin-patches wrote:
> > On 5/18/2020 1:36 AM, Takashi Yano via Cygwin-patches wrote:
> >> On Mon, 18 May 2020 14:25:19 +0900
> >> Takashi Yano via Cygwin-patches <cygwin-patches@cygwin.com> wrote:
> >>> However, mc hangs by several operations.
> >>>
> >>> To reproduce this:
> >>> 1. Start mc with 'env SHELL=tcsh mc -a'
> >>
> >> I mean 'env SHELL=/bin/tcsh mc -a'
> >>
> >>> 2. Select a file using up/down cursor keys.
> >>> 3. Press F3 (View) key.
> > 
> > Thanks for the report.  I can reproduce the problem and will look into it.
> 
> I'm not convinced that this is a FIFO bug.  I tried two things.
> 
> 1. I attached gdb to mc while it was hanging and got the following backtrace 
> (abbreviated):
> 
> #1  0x00007ff901638037 in WaitForMultipleObjectsEx ()
> #2  0x00007ff901637f1e in WaitForMultipleObjects ()
> #3  0x0000000180048df5 in cygwait () at ...winsup/cygwin/cygwait.cc:75
> #4  0x000000018019b1c0 in wait4 () at ...winsup/cygwin/wait.cc:80
> #5  0x000000018019afea in waitpid () at ...winsup/cygwin/wait.cc:28
> #6  0x000000018017d2d8 in pclose () at ...winsup/cygwin/syscalls.cc:4627
> #7  0x000000018015943b in _sigfe () at sigfe.s:35
> #8  0x000000010040d002 in get_popen_information () at filemanager/ext.c:561
> [...]
> 
> So pclose is blocking after calling waitpid.  As far as I can tell from looking 
> at backtraces of all threads, there are no FIFOs open.
> 
> 2. I ran mc under strace (after exporting SHELL=/bin/tcsh), and I didn't see 
> anything suspicious involving FIFOs.  But I saw many EBADF errors from fstat and 
> close that don't appear to be related to FIFOs.
> 
> So my best guess at this point is that the FIFO changes just exposed some 
> unrelated bug(s).
> 
> Prior to the FIFO changes, mc would get an error when it tried to open tcsh_fifo 
> the second time, and it would then set
> 
>    mc_global.tty.use_subshell = FALSE;
> 
> see the mc source file subshell/common.c:1087.

I looked into this problem and found pclose() stucks if FIFO
is opened.

Attached is a simple test case. It works under cygwin 3.1.4,
but stucks at pclose() under cygwin git head.

Isn't this a FIFO related issue?

-- 
Takashi Yano <takashi.yano@nifty.ne.jp>
-------------- next part --------------
A non-text attachment was scrubbed...
Name: mc-minimal.c
Type: text/x-csrc
Size: 712 bytes
Desc: not available
URL: <https://cygwin.com/pipermail/cygwin-patches/attachments/20200519/c9658c8d/attachment.bin>


More information about the Cygwin-patches mailing list