You are an expert in writing code in many different languages. Your goal is to perform code completion for the following code, keeping in mind the rest of the code and the file meta data.
    Metadata details:
    filename: local.go
    path of file: ./repos/mgmt/engine/local
    
    the code of the file until where you have to start completion: // Mgmt
// Copyright (C) 2013-2024+ James Shubin and the project contributors
// Written by James Shubin <james@shubin.ca> and the project contributors
//
// This program is free software: you can redistribute it and/or modify
// it under the terms of the GNU General Public License as published by
// the Free Software Foundation, either version 3 of the License, or
// (at your option) any later version.
//
// This program is distributed in the hope that it will be useful,
// but WITHOUT A
    
func (obj *Value) getPrefix() (string, error) {
	// NOTE: Moving this mutex to just below the first early return, would
	// be a benign race, but as it turns out, it's possible that a compiler
	// would see this behaviour as "undefined" and things might not work as
	// intended. It could perhaps be replaced with a sync/atomic primitive
	// if we wanted better performance here.
	obj.mutex.Lock()
	defer obj.mutex.Unlock()

	if obj.prefixExists { // former race read
		return obj.prefix, nil
	}

	// MkdirAll instead of Mkdir because we have no idea if the parent
	// local/ directory was already made yet or not. (If at all.) If path is
	// already a directory, MkdirAll does nothing and returns nil. (Good!)
	// TODO: I hope MkdirAll is thread-safe on path creation in case another
	// future local API tries to make the base (parent) directory too!
	if err := os.MkdirAll(obj.prefix, 0755); err != nil {
		return "", err
	}
	obj.prefixExists = true // former race write

	return obj.prefix, nil
}