Question

I have this question.

public class Foo : object
{
    public override bool Equals(obj a, objb)
    {
       return ((Foo)a).Bar.GetHashCode() == ((Foo)b).Bar.GetHashCode();
}

}

Suppose I want to make Foo threadsafe. Do I need to synchronize calls to GetHashCode()?

Answer 1

Even if you were going to add synchronization, what would you synchronize against?

I would say as a general rule GetHashCode should always be threadsafe, but the docs don’t state a requirement for thread safety. A consumer of Bar can’t really guarantee it’s usage is threadsafe unless Bar provides thread safety internally.

Let’s say Bar uses two internal fields to calculate the hash code. If another thread is in the process of updating the fields and only one has changed, you’ll be able to get a GetHashCode() result after one field was updated but before the second was updated, unless Bar internally provides synchronization.