Are mutations through an unmodified atomic reference visible?

Question

Let's say I have an atomic reference to a mutable class type Foo:

AtomicReference<Foo> foo = new AtomicReference<Foo>(new Foo());

Thread A writes to the Foo object:

foo.get().write(42);

And thread B reads from the Foo object:

int x = foo.get().read();

Note that the atomic reference itself is never modified! That is, I do not call foo.set in my code.

Is thread B guaranteed to observe the value that was last written by thread A?

Answer 1

Is thread B guaranteed to observe the value that was last written by thread A?

No. It would be equivalent to:

volatile Foo foo = new Foo();
foo.write(42);

All writes that happen prior to the initial assignment of foo will be visible after foo is non-null. After that however there is no guarantee on when a thread will see the write of foo.write(42) to occur.