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: mq.go
    path of file: ./repos/faasd/vendor/github.com/Microsoft/hcsshim/internal/queue
    
    the code of the file until where you have to start completion: package queue

import (
	"errors"
	"sync"
)

var ErrQueueClosed = errors.New("the queue is closed for reading and writing")

// Message
    
func (mq *MessageQueue) Enqueue(msg interface{}) error {
	mq.m.Lock()
	defer mq.m.Unlock()

	if mq.closed {
		return ErrQueueClosed
	}
	mq.messages = append(mq.messages, msg)
	// Signal a waiter that there is now a value available in the queue.
	mq.c.Signal()
	return nil
}