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Date: Thu, 2 Jul 2020 19:50:06 +0200
Message-ID: <CA+7cx1o2huaWH6s4cuwzyYQVuFgAJNBsi_bVWDdCzn-W-EAhUQ@mail.gmail.com>
Subject: Re: name pipe problem: 1 writer, multiple concurrent readers
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From: =?utf-8?q?Morten_Kj=C3=A6rulff_via_Cygwin?= <cygwin AT cygwin DOT com>
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>
> On 5/19/2020 11:20 AM, Morten Kjærulff wrote:
> > On Tue, May 19, 2020 at 3:55 PM Ken Brown via Cygwin <cygwin AT cygwin DOT com> wrote:
> >>
> >> On 5/19/2020 7:26 AM, Morten Kjærulff via Cygwin wrote:
> >>> Hi,
> >>>
> >>> The following script:
> >>>
> >>> #!/bin/sh
> >>>
> >>> rm -f t.pip t.txt
> >>>
> >>> mkfifo t.pip
> >>> printf "line1\nline2\n" >t.txt
> >>>
> >>> ps
> >>>
> >>> {
> >>>     while true ; do
> >>>       cp t.txt t.pip
> >>>     done
> >>> } &
> >>>
> >>> rm -f t.rc.*
> >>> for rc in 0 1 2 3 4 5 6 7 8 9 ; do
> >>>     {
> >>>       diff t.pip t.txt
> >>>       echo $? >t.rc.$rc
> >>>     }
> >>> done
> >>> echo result1 start
> >>> ls  t.rc.* | wc -l
> >>> cat t.rc.*
> >>> echo result1 end
> >>>
> >>> rm -f t.rc.*
> >>> for rc in 0 1 2 3 4 5 6 7 8 9 ; do
> >>>     {
> >>>       diff t.pip t.txt
> >>>       echo $? >t.rc.$rc
> >>>     } & # run the readers in parallel
> >>> done
> >>> sleep 10
> >>> echo result2 start
> >>> ls  t.rc.* | wc -l
> >>> cat t.rc.*
> >>> echo result2 end
> >>>
> >>> ps
> >>>
> >>> Give me output like this:
> >>>
> >>> $ ./tpip.sh
> >>>         PID    PPID    PGID     WINPID   TTY         UID    STIME COMMAND
> >>>        1642    1600    1642      65264  cons1    1058872 13:18:58 /usr/bin/sh
> >>>        1600       1    1600      72728  cons1    1058872 13:18:33 /usr/bin/bash
> >>>        1645    1642    1642      42088  cons1    1058872 13:18:58 /usr/bin/ps
> >>> result1 start
> >>> 10
> >>> 0
> >>> 0
> >>> 0
> >>> 0
> >>> 0
> >>> 0
> >>> 0
> >>> 0
> >>> 0
> >>> 0
> >>> result1 end
> >>> 0a1,2
> >>>> line1
> >>>> line2
> >>> diff: t.pip
> >>> result2 start
> >>> 1
> >>> 2
> >>> result2 end
> >>>         PID    PPID    PGID     WINPID   TTY         UID    STIME COMMAND
> >>>        1690    1688    1642     104032  cons1    1058872 13:19:01 /usr/bin/diff
> >>>        1681    1642    1642      95012  cons1    1058872 13:19:00 /usr/bin/sh
> >>>        1642    1600    1642      65264  cons1    1058872 13:18:58 /usr/bin/sh
> >>>        1684    1681    1642      99624  cons1    1058872 13:19:00 /usr/bin/diff
> >>>        1678    1676    1642      94532  cons1    1058872 13:19:00 /usr/bin/diff
> >>>        1688    1642    1642      88864  cons1    1058872 13:19:01 /usr/bin/sh
> >>>        1698    1642    1642     104820  cons1    1058872 13:19:11 /usr/bin/ps
> >>>        1692    1642    1642      66572  cons1    1058872 13:19:01 /usr/bin/sh
> >>>        1677    1674    1642      86692  cons1    1058872 13:19:00 /usr/bin/diff
> >>>        1646    1642    1642      30888  cons1    1058872 13:18:58 /usr/bin/sh
> >>>        1600       1    1600      72728  cons1    1058872 13:18:33 /usr/bin/bash
> >>>        1686    1685    1642      14320  cons1    1058872 13:19:01 /usr/bin/diff
> >>>        1685    1642    1642      25608  cons1    1058872 13:19:00 /usr/bin/sh
> >>>        1676    1642    1642     104212  cons1    1058872 13:19:00 /usr/bin/sh
> >>>        1689    1642    1642      98004  cons1    1058872 13:19:01 /usr/bin/sh
> >>>        1674    1642    1642      44152  cons1    1058872 13:19:00 /usr/bin/sh
> >>>        1680    1646    1642      28224  cons1    1058872 13:19:00 /usr/bin/cp
> >>>        1682    1679    1642      43612  cons1    1058872 13:19:00 /usr/bin/diff
> >>>        1694    1692    1642      67736  cons1    1058872 13:19:01 /usr/bin/diff
> >>>        1683    1642    1642      93544  cons1    1058872 13:19:00 /usr/bin/sh
> >>>        1679    1642    1642      90188  cons1    1058872 13:19:00 /usr/bin/sh
> >>>        1691    1689    1642      68560  cons1    1058872 13:19:01 /usr/bin/diff
> >>>        1687    1683    1642      83952  cons1    1058872 13:19:01 /usr/bin/diff
> >>>
> >>> $
> >>>
> >>> That is, when I run the readers in sequence, no problem, but when I
> >>> run the in parallel, they either hang or t.pip seems empty.
> >>
> >> The current cygwin release doesn't support multiple concurrent readers of a
> >> FIFO.  I have recently added that support, which should appear in the next
> >> release, although there are still bugs to be fixed.  See
> >>
> >>     https://cygwin.com/pipermail/cygwin-patches/2020q2/010195.html
> >>
> >> Ken
> > Great!
>
> Let's keep the discussion on the mailing list
> > Then we will have a read-only file (pipe), which is the output of an
> > abitrary command, right?
>
> Yes.
>
> > Can we have multiple concurrent writers and one reader, which would
> > become a write-only file, which becomes the input of an abitrary
> > command?
>
> That already exists, although I found and fixed some bugs when I was developing
> the multiple reader support.
>
> > Anywhere I can see the plans for next release, if any?
>
> That's up to Corinna.
>
> Ken

I think we got a new release around the beginning of June, right?
You said that there were still issues (I can confirm).
If it can help, here is the output I see today of above scripts:

$ ./tp.sh
      PID    PPID    PGID     WINPID   TTY         UID    STIME COMMAND
     1766    1763    1763     136424  cons1    1058872 19:48:52 /usr/bin/ps
     1708       1    1708     141992  cons1    1058872 19:42:22 /usr/bin/bash
     1763    1708    1763     146792  cons1    1058872 19:48:52 /usr/bin/sh
result1 start
10
0
0
0
0
0
0
0
0
0
0
result1 end
0a1,2
> line1
> line2
      0 [fifo_reader] diff 1806 C:\cygwin\bin\diff.exe: *** fatal
error - Can't update my handlers, Win32 error 87
result2 start
4
0
1
0
0
result2 end
      PID    PPID    PGID     WINPID   TTY         UID    STIME COMMAND
     1815    1763    1763     110264  cons1    1058872 19:48:56 /usr/bin/sh
     1809    1807    1763     136060  cons1    1058872 19:48:56 /usr/bin/diff
     1813    1767    1763     143812  cons1    1058872 19:48:56 /usr/bin/cp
     1814    1811    1763      88380  cons1    1058872 19:48:56 /usr/bin/diff
     1805    1802    1763     152044  cons1    1058872 19:48:56 /usr/bin/diff
     1811    1763    1763     133876  cons1    1058872 19:48:56 /usr/bin/sh
     1708       1    1708     141992  cons1    1058872 19:42:22 /usr/bin/bash
     1767    1763    1763     121096  cons1    1058872 19:48:53 /usr/bin/sh
     1806    1804    1763     148760  cons1    1058872 19:48:56 /usr/bin/diff
     1810    1763    1763       4740  cons1    1058872 19:48:56 /usr/bin/sh
     1807    1763    1763     121336  cons1    1058872 19:48:56 /usr/bin/sh
     1804    1763    1763     120764  cons1    1058872 19:48:55 /usr/bin/sh
     1802    1763    1763     108068  cons1    1058872 19:48:55 /usr/bin/sh
     1821    1763    1763      72428  cons1    1058872 19:49:06 /usr/bin/ps
     1816    1815    1763     115876  cons1    1058872 19:48:56 /usr/bin/diff
     1812    1810    1763      96120  cons1    1058872 19:48:56 /usr/bin/diff
     1763    1708    1763     146792  cons1    1058872 19:48:52 /usr/bin/sh

/Morten
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