function log(message, primary_only = true) {
    if (primary_only && cluster.isWorker) return;
    console.log(`[${process.pid}] ${message}`);
}
Logs a message to the console.
Will only log if the current process is a worker and primary_only is set to false.

@param {String} message
@param {Boolean} [primary_only=true]
@returns