shallow-copy a segment of a value type array
-
07-07-2021 - |
Question
I'm trying to shallow-copy a double[] into segments, and pass those segments to new threads, like so:
for (int i = 0; i < threadsArray.Length; i++)
{
sub[i] = new double[4];
//Doesn't shallow copy since double is a value type
Array.Copy(full, i * 4, sub[i], 0, 4);
double[] tempSub = sub[i];
threadsArray[i] = new Thread(() => DoStuff(tempSub));
threadsArray[i].Start();
}
What would be the best way to have the created segments reference the original array?
La solution
You could use the ArraySegment<T>
structure:
for (int i = 0; i < threadsArray.Length; i++)
{
sub[i] = new ArraySegment<double>(full, i * 4, 4);
ArraySegment<double> tempSub = sub[i];
threadsArray[i] = new Thread(() => DoStuff(tempSub));
threadsArray[i].Start();
}
(note that you will need to change the signature of DoStuff
to accept an ArraySegment<double>
(or at least an IList<double>
instead of an array)
ArraySegment<T>
doesn't copy the data; it just represents an segment of the array, by keeping a reference to the original array, an offset and a count. Since .NET 4.5 it implements IList<T>
, which means you can use it without worrying about manipulating the offset and count.
In pre-.NET 4.5, you can create an extension method to allow easy enumeration of the ArraySegment<T>
:
public static IEnumerable<T> AsEnumerable<T>(this ArraySegment<T> segment)
{
for (int i = 0; i < segment.Count; i++)
{
yield return segment.Array[segment.Offset + i];
}
}
...
ArraySegment<double> segment = ...
foreach (double d in segment.AsEnumerable())
{
...
}
If you need to access the items by index, you will need to create a wrapper that implements IList<T>
. Here's a simple implementation: http://pastebin.com/cRcpBemQ