Is a C# generic dictionary of structs thread safe if it doesn't resize?

Question

If I preload a dictionary with structs and guarantee never to add any more items to it, will it be thread-safe if I update items from a single thread and read them from another.

struct DataItem
{
    public double Price;
    public double Size;
}

class Test
{
    Dictionary<string, DataItem> items = new Dictionary<string,DataItem>(3);
    public Test ()
    {
        items["A"] = new DataItem(){Price=100, Size=1000};
        items["B"] = new DataItem(){Price=200, Size=2000};
        items["C"] = new DataItem(){Price=300, Size=3000};
    }

One thread would call this method

    public void UpdateItem()
    {
        DataItem newItem = new DataItem(){Price=400, Size=4000};
        items["A"] = newItem;    
    }

A different thread would be calling this method

    public DataItem GetItem(string key)
    {
        return items[key];
    }
}

Answer 1

The documentation says:

A Dictionary<TKey, TValue> can support multiple readers concurrently, as long as the collection is not modified.

So it is not threadsafe to have both readers and writers operating simultaneously.