How thread safe are immutable objects?

Question

Everybody says that immutable objects are thread safe, but why is this?

Take the following scenario running on a multi core CPU:

• Core

Answer 1

The object's immutability isn't the real question in your scenario. Rather, your description's issue revolves around the reference, list, or other system which points to the object. It would of course need some sort of technique to make sure the old object is no longer availble to the thread which may have tried to access it.

The real point to immutable object's thread safety is that you don't need to write a bunch of code to produce thread safety. Rather the framework, OS, CPU (and whatever else) do the work for you.