Not closing stdout when setting clipboard from stdin

[astrand]

xclip does not appear to be closing stdout. This was noticed to cause compatibility problems when used with newer versions of tmux.

The tmux developer was able to identify this as the cause of an issue originally reported against tmux.

More info: https://sourceforge.net/p/tmux/tickets/40/?limit=10&page=1#9a2b

Reported by: wadetc

Original Ticket: xclip/bugs/9

[astrand]

See this StackOverflow question for an explanation of why xclip does not exit/close stdout until another selection is made:

http://stackoverflow.com/questions/19254114/xclip-does-not-terminate-when-tracing-it

Basically, it seems the only place the text buffer exists for other X clients to copy from is xclip itself, so if it exits the text goes with it. To stay alive, xclip fork's and daemonizes. I'm not sure how xsel handles this.

I guess maybe xclip could close stdout when it knows it has nothing else to write to it?

Original comment by: jaredcasper

[Ian2020]

I'm not a C developer but xsel's (github.com) function set_selection__daemon around line 1770 seems to suggest it uses a similar daemon approach:

[create] a daemon process to handle selection requests for the specified selection

The daemon can have a timeout set via the selectionTimeout flag but the default is no timeout:

--selectionTimeout ms
specify the timeout in milliseconds within which the selection must be retrieved. A value of 0 (zero)
specifies no timeout (default)

So presumably the daemon remains as long as it's needed, just like xclip.

Using xsel is suggested as a fix for this issue in the Tmux article on ArchWiki so perhaps the real difference between the two is just the closing of stdout as @astrand suggests above?

[murlakatamenka]

This issue won't let parent shell process exit, i.e.:

echo foo | xclip
exit # won't exit unless xclip process spawned above exits

As a workaround one can wrap xclip this way (.zshrc):

xclip() {
    /usr/bin/xclip "$@" &> /dev/null
}

&> /dev/null is zsh / bash way of redirecting both stdout and stdin.
> /dev/null 2&>1 for more portable way.

[ljrk0]

Cross-posting my solution from #34 (comment)_ , simply closing stdout/stderr using the shell works as well:

Closing stdout and stderr when running xclip with >&- 2>&- seems to do the trick.

[murlakatamenka]

@leonardkoenig didn't know if such possibility.

Another one I found is to use nohup (https://linux.die.net/man/1/nohup).

[hackerb9]

I'm having the darnedest time trying to reproduce this bug. I've tried setting my shell to zsh and compiling old versions of xclip. And yet, I'm always able to just type 'exit' to logout. @murlakatamenka, @leonardkoenig, could you please provide a little bit more information about how to trigger this bug? What exactly is hanging? Is it ssh? Or does your shell say something like "you have running jobs"? Which shell are you using? What version of xclip?

[hackerb9]

I see that "nohup" is given as a solution. Should I presume it only works because it redirects stdout to a file? If not, then perhaps xclip could call setsid() as the child after forking (as suggested in #4). `