Question

This is possibly a silly question, but do I need to use and assignment with a lock, or can I simply return the results.

For example:

I have a private helper method that returns an IEnumerable list of file names. It uses a lock to ensure the method is thread safe while it is iterating around the m_transfers collection.

Do I need an assignment…

IEnumerable<String> updated;
lock (m_transfers.Lock)
{
    updated = m_transfers.Values.Where(transfer => transfer.Updated)
                         .Select(transfer => transfer.Filename);
}
return updated;

Or can I just do

lock (m_transfers.Lock)
{
    return updated = m_transfers.Values.Where(transfer => transfer.Updated)
                            .Select(transfer => transfer.Filename);
}

Answer 1

No, you don’t need to add an extra variable; the semantic is the same either way, since in either case we only actually return the value once we have relinquished the lock.

Since the variable doesn’t serve a purpose, I would remove it and use the second version – although technically, the compiler actually puts it back in anyway (a lock involves a try/finally, and at the IL level you can’t ret from inside a try; so the compiler actually writes it like your first version).