name pipe problem: 1 writer, multiple concurrent readers
Ken Brown
kbrown@cornell.edu
Tue May 19 13:14:04 GMT 2020
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
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