Question

I can’t find the answer but it’s a simple question:

Is it safe for two threads to read the value of a pointer to a user-defined object in c++ at the same time with no locks or any other shenanigans?

Answer 1

Yes. Actually it is safe to read any values (of builtin type) concurrently.

Data races can only occur, if a value is modified concurrently with some other thread using it. The key statements from the Standard for this are:

A data race is defined in §1.10/21:

The execution of a program contains a data race if it contains two
conflicting actions in different threads, at least one of which is not
atomic, and neither happens before the other.

where conflicting is defined in §1.10/4:

Two expression evaluations conflict if one of them modifies a memory
location (1.7) and the other one accesses or modifies the same memory
location.

So you must use suitable synchronization between those reads and any writes.