Are static variables thread-safe? C#

It appears as though all you want to do is load it once and keep a reference to it. All you need to guard is initialising the variable if it’s null. Null checking, locking and null checking again is called Double Check Locking and will work well for you. It’s best practice to provide a separate locking object, so you have good control over granularity of locks.

Note this doesn’t stop people from mutating the value inside the DataTable it only stops people from trying to initialise the static member at the same time.

private static readonly object UnitTableLock = new object();
private static DataTable unitTable;
private static bool _ready = false;

public static DataTable GetUnitList()
{
    if (!_ready)
    {
        lock (UnitTableLock)
        {
            if (!_ready)
            {
                unitTable = new DataTable; //... etc
                System.Threading.Thread.MemoryBarrier();
                _ready = true;
            }
        }
    }

    return unitTable;
}

Only read from the result of GetUnitList never write to it.

Amended with reference to http://en.wikipedia.org/wiki/Double-checked_locking