public void execute(Key key, Runnable command) {
        synchronized (commands) {
            if (null == commands.putIfAbsent(key, new ArrayDeque<>(List.of(command))))
                executor.execute(() -> runAll(key));
            else
                commands.get(key).add(command);
        }
    }
Executes the given command. If other commands are already running or queued for the given key,
execution of this command happens after those, on the same thread as is running them.
<p>
Any exception thrown by the command will only be logged, to allow subsequent commands to run.
vespajlib/src/main/java/com/yahoo/concurrent/StripedExecutor.java