[konsole] [Bug 447455] New: Blocks processes producing too much output when window not in active tty

[Daniel Dawson]

https://bugs.kde.org/show_bug.cgi?id=447455

            Bug ID: 447455
           Summary: Blocks processes producing too much output when window
                    not in active tty
           Product: konsole
           Version: 21.12.0
          Platform: Gentoo Packages
                OS: Linux
            Status: REPORTED
          Severity: normal
          Priority: NOR
         Component: emulation
          Assignee: konsole-devel at kde.org
          Reporter: danielcdawson at gmail.com
  Target Milestone: ---

SUMMARY
If I switch to a different tty from the one a Konsole window is on, I find that
any child processes producing output get blocked after a certain amount is
produced.

STEPS TO REPRODUCE
1. Login on a virtual console (e.g. tty1).
2. Prepare a way to get output from a process. The way I did this was:
  $ mknod /tmp/test.pipe p
  $ cat /tmp/test.pipe
3. Start a graphical session, or switch back to one.
4. Start a terminal emulator, such as Konsole, and do something in it that both
produces output on stdout, and sends it to the VC:
  $ for ((i=0;;i++)); do echo $i; sleep 0.005; done | tee /tmp/test.pipe  #
sleep is optional, but recommended.
5. Switch back to the VC, and watch the output.

OBSERVED RESULT
When using Konsole, after a couple thousand lines, the output pauses. Only once
I switch back to the graphical session, does output continue. I tried this also
with xterm and LXTerminal (since they happen to be installed), and this
behavior does not occur with them (unless their buffers are just really huge).

EXPECTED RESULT
Not being in the active tty should, I believe, not affect child processes
simply because of their terminal output. This is a problem if running an
application under Konsole that's doing something important while writing to
stderr/stdout.

SOFTWARE/OS VERSIONS
Linux/KDE Plasma: 5.15.0-gentoo (64-bit) [custom config]
(available in About System)
KDE Plasma Version: 5.23.4
KDE Frameworks Version: 5.89.0
Qt Version: 5.15.2

ADDITIONAL INFORMATION
A workaround seems to be to run things that need to avoid being blocked under
something like screen or tmux, since they take over as the controlling
terminal, and keep running even if their front-end disappears.

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