The problem#

I want my computer to act differently when I'm actively using it as opposed to away from. I almost always lock the screen when I step away from my computer, so I want to have the same signal do more than just start the screensaver.

The solution#

Save the follow script which is slightly modified from the example in the man page for xscreensaver-command as watch-xscreensaver.pl:

#!/usr/bin/perl

my $blanked = 0;
open (IN, "xscreensaver-command -watch |");
while (<IN>) {
    print;
    if (m/^(BLANK|LOCK)/) {
        if (!$blanked) {
            system "on-xscreensaver-lock";
            $blanked = 1;
        }
    } elsif (m/^UNBLANK/) {
        system "on-xscreensaver-unlock";
        $blanked = 0;
    }
}
if ($blanked) {
    system "on-xscreensaver-unlock";
}

Either call it from your ~/.xsessionrc file or just manually run from a terminal in your X session. I run it from a screen session so I can reattach to it and see the output:

screen -d -m -S xscreensaver-watch watch-xscreensaver.pl

My on-xscreensaver-lock and on-xscreensaver-unlock scripts are below and may be a good starting place, but yours will probably be different depending on your needs.

The details#

The problem#

Working on the same screensaver as yesterday, we want to minimize CPU usage. Since the screensaver is a clock showing hours and minutes, there's no need to do anything except once a minute to change the time display. Optimally, the process would only be scheduled once a minute, exactly when the minute changed, to draw the screen.

The problem#

I was modifying a screensaver written using SDL and noticed that sometimes there were many instances of it left running, even after unlocking the screen. Another bug was causing the screensaver to use 100% CPU, resulting in it using up all of my processing power just for a simple screensaver.

The solution#

Make the program exit immediately when it receives a SIGTERM signal by including the function

void exitImmediately(int sig) {
    abort();
}

and making the SIGTERM signal handler call it:

signal(SIGTERM, exitImmediately);