Updates the dict of gunicorn processes. Run the ps command and parse its
    output for processes named after gunicorn, building up a dict of gunicorn
    processes. When new gunicorns are discovered, run the netstat command to
    determine the ports they're serving on.

def update_gunicorns():
    """
    Updates the dict of gunicorn processes. Run the ps command and parse its
    output for processes named after gunicorn, building up a dict of gunicorn
    processes. When new gunicorns are discovered, run the netstat command to
    determine the ports they're serving on.
    """
    global tick
    tick += 1
    if (tick * screen_delay) % ps_delay != 0:
        return
    tick = 0
    for pid in gunicorns:
        gunicorns[pid].update({"workers": 0, "mem": 0})
    ps = Popen(PS_ARGS, stdout=PIPE).communicate()[0].split("\n")
    headings = ps.pop(0).split()
    name_col = headings.index(cmd_heading)
    num_cols = len(headings) - 1
    for row in ps:
        cols = row.split(None, num_cols)
        if cols and "gunicorn: " in cols[name_col]:
            if "gunicorn: worker" in cols[name_col]:
                is_worker = True
            else:
                is_worker = False

            if is_worker:
                pid = cols[headings.index("PPID")]
            else:
                pid = cols[headings.index("PID")]
            if pid not in gunicorns:
                gunicorns[pid] = {"workers": 0, "mem": 0, "port": None, "name":
                    cols[name_col].strip().split("[",1)[1].split("]",1)[:-1]}
            gunicorns[pid]["mem"] += int(cols[headings.index("RSS")])
            if is_worker:
                gunicorns[pid]["workers"] += 1
    # Remove gunicorns that were not found in the process list.
    for pid in gunicorns.keys()[:]:
        if gunicorns[pid]["workers"] == 0:
            del gunicorns[pid]
    # Determine ports if any are missing.
    if not [g for g in gunicorns.values() if g["port"] is None]:
        return
    for (pid, port) in ports_for_pids(gunicorns.keys()):
        if pid in gunicorns:
            gunicorns[pid]["port"] = port