Question

Are the internals of a delegate to the Task Parallel Library thread safe – i.e. is that value of a variable declared within that delegate isolated to that thread?

Example:

Parallel.ForEach(collection, item => {
    var something = new Something(item.Property);
});

Is something guaranteed to always be a unique to a thread, protected against being overwritten by another thread created by the same Parallel operation?

Answer 1

Since this is a delegate something is a local variable and certainly thread-safe if it is of a value type – of course it can still be overwritten if the variable holds a reference to a shared reference object (e.g. a reference to a variable that the delegate uses as a closure)