[PATCH 00/21] FIFO: Support multiple readers
Tue May 19 06:15:35 GMT 2020
On Tue, 19 May 2020 10:26:09 +0900
Takashi Yano via Cygwin-patches <email@example.com> wrote:
> Hi Ken,
> On Mon, 18 May 2020 13:42:19 -0400
> Ken Brown via Cygwin-patches <firstname.lastname@example.org> 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 <email@example.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?
In the test case, fhandler_fifo::close() called from /bin/true
seems to get into infinite loop at:
while (inc_nreaders () > 0 && !found);
Takashi Yano <firstname.lastname@example.org>
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