defermap

This is a simple preload library for adding deferred mapping to xterm. Deferred mapping just means that a program is running, but the window is not visible.

You might want this on systems where xterm is annoyingly slow to start. This approach can make an it appear near instantly, even on the slowest systems.

The idea is to cache a few xterms in the background, then when you want a new terminal, all the slow stuff will already be done and you can start typing immediately.

Installation

You can simply copy defermap.so to /usr/lib, or run make install as root.

To uninstall it, just remove the file.

Usage

You need something to manage the cache for you in the background, xargs will work.

Try running a command like this:

$ xargs --null --arg-file=/dev/zero --max-procs=3 --replace -- \
     env LD_PRELOAD=defermap.so xterm -display :0 [PARAMS...]

This will keep three xterms running in the background.

Note: If you often rapidly start terminals in quick succession, increase max-procs.

When you want a new terminal, instead of running xterm as you normally would, do this instead:

$ pkill --oldest --signal SIGUSR1 xtermserver

An xterm should appear near-instantly.

If you decide you like this, you can make xterm an alias to this.

Advanced

• You can adjust the number of xterms cached dynamically at runtime.

Note: This is an xargs feature, see here for details.

You simply send xargs a SIGUSR1 to increase the cache size, and a SIGUSR2 to decrease it.

$ pkill --signal SIGUSR1 xargs # increase number of cached xterms
$ pkill --signal SIGUSR2 xargs # decrease number of cached xterms

• I print reminders in my .bashrc, so don't want xterms sitting in the cache for too long.

I reap them if they're unused after a few hours, if you don't like this, edit kIdleTimeout in defermap.c.

• If you use a shell function instead of an alias, you can add a fallback in case the server isn't running.

$ xterm() { pkill --oldest --signal SIGUSR1 xtermserver || /usr/bin/xterm; }

Startup

If you want this to run in the background, you can do something like this in your .xinitrc or similar startup script (please excuse the comically long commandline):

$ start-stop-daemon --startas xargs                 \
                    --background                    \
                    --make-pidfile                  \
                    --pidfile ~/.xtermserver.pid    \
                    --chdir $HOME                   \
                    --quiet                         \
                    --start                         \
                    -- --null                       \
                       --arg-file=/dev/zero         \
                       --max-procs=3                \
                       --replace                    \
                       -- env LD_PRELOAD=defermap.so xterm -display :0 [...]

You probably also want an alias or shell function to invoke it, something like this:

$ alias xterm="pkill --oldest --signal SIGUSR1 xtermserver"

Naturally, you can also bind this command to some keystroke in your window manager.

Contact

Contact taviso@gmail.com with questions/comments.