The Interlocked class

Working with threads and counters can because a really pain if you do not take care. Fortunately for us, .Net supplies us with a couple of methods that can make our life a little bit easier. The class Interlocked, which can be found in System.Thread allows you to increment, decrement, and set the value of an int or long as an atomic action, thus preventing race conditions where multiple threads update the same counter at the same time.

The first methods are of course, Increment() and Decrement(), both accepting an int or long variable and update it as requested. The next method is the Exchange(), which allow you to set the value of either an int, a long or object variable, by passing it the variable by reference, and the next requested value.

Another interesting method in the CompareExchange(). This method checks if the value of the variable is as expected, and only then update it. The method returns the current value of the variable, whether it was updated or not, allowing you to redo you calculations if the value changed while you were calculating the new value.

Below is an example take from MSDN:

public int AddToTotal(int addend)
{
    int initialValue, computedValue;
    do
    {
        initialValue = totalValue;
        computedValue = initialValue + addend;
    }
    while (initialValue != Interlocked.CompareExchange(ref totalValue, computedValue, initialValue));
    return computedValue;
}