Already-running process notifications

The tool described in the last post (X11 urgency hint and notifications) works well, but there's a common use case it does not support: completion notification of already-running process. That post describes how to be notified when a build completes:

make; seturgent

But what if we already started the build? Another helper tool is required. Here it is:

# As is, this can't be an external utility since it uses the shell builtin
# 'wait', which only works on direct children of this shell. An external utility
# creates another shell, so this doesn't work
function waitfor()
{
    # waits for a process to exit, and sets urgency when that happens. Expects a
    # single pgrep-able argument on the commandline. If no argument is given,
    # it'll look for the only child process.

    # if this process is a child of this shell, I use a blocking wait.
    # Otherwise, I poll.

    PID_ALL=$(pgrep -s0 -f $1)

    # filter out the current process (the shell) and 'xclip'. I have xclip
    # zombies apparently
    PID=$(comm -23 <(echo $PID_ALL | sort) <(echo $$ `pidof xclip` | xargs -n1 | sort))
    N=$(echo $PID | wc -w)

    if [[ $N -eq 1 ]]; then
        echo "Found unique process with pid $PID"
        kill -CONT $PID # resume this process, since it's almost certainly
                        # paused right now
        wait $PID;
        seturgent
        true
    elif [[ $N -ne 0 ]]; then
        echo "Found more than one matching process. Doing nothing";
        false
    elif [[ -z $1 ]]; then
        echo "No children of the current shell to wait on. Doing nothing";
        false
    else
        echo "Found no matching processes in this shell. Looking globally.";
        PID=$(pgrep -f $1)
        N=$(echo $PID | wc -w)
        if [[ $N -eq 0 ]]; then
            echo "Found no matching global process either. Giving up.";
            false
        elif [[ $N -ne 1 ]]; then
            echo "Found more than one global process. Giving up";
            false
        else
            echo "Found unique process with pid $PID"
            while (ps -p $PID > /dev/null) { sleep 10; }
            seturgent;
            true
        fi
    fi
}

This is a zsh shell script that lives in my .zshrc.

• with no argument, it acts on the only child of this shell
• with an argument, it uses pgrep to find a matching process, first in the local shell, then outside of the local shell

Once the target process is identified, the script waits for the process to exit, then it sets the urgency hint on the terminal emulator window. If there's any ambiguity about which process is being targeted, nothing is done.

The most common use case: if a long-running process is currently active, one would temporarily suspend it with C-z, then issue a waitfor. This re-activates the process, and sets the urgency when finished. One could also re-implement the use case from the previous post as

make & waitfor

As said previously, this is a zsh script. It probably needs to be tweaked a little bit to work in bash, but I have not done this.

The reason this is a shell script, is that the wait-for-this-process-to-finish operation on Linux only works from the parent of the process being waited on. As implemented, waitfor() doesn't spawn a new process, and runs in the shell process itself, which is the parent of the thing being waited on. If this was anything other than a shell script, then the waiter would also be a child of the shell, so the process being waited on, and the process doing the waiting would be siblings. The script works that case too, but it polls every 10 seconds, instead of being notified of completion.

I've been using this for a little bit. It's not perfect, and there're some warts I'd like to fix. Still, it does the job, and it's already something I use every day.