This is the "technical meaning" of "undefined behaviour" according to Wikipedia:

> Undefined behavior (UB) is the result of executing a program whose behavior is prescribed to be unpredictable, in the language specification to which the computer code adheres.

Can we predict the behavior of a Java program with a data race?

A section of Java code with a data race can’t break anything that the same section of code couldn’t have been rewritten to intentionally break without using a data race. For example: it might throw an exception, loop infinitely, or return valid values that the programmer didn’t expect; but it cannot corrupt the internal state of the JVM, violate type-safety, fiddle with private fields, or access data that isn’t reachable from its own variables. Data races cannot be used to violate a security barrier between mutually untrusting sections of Java code.

You're right. That's a big advantage of the JVM. It's memory safe even in presence of data races.

That post from Russ Cox (again) explains quite well why Go is not memory safe in presence of data races, and what should be changed to fix this: https://research.swtch.com/gorace

That's less a definition, and more a description of what UB looks like.

Here's a better definition: https://en.cppreference.com/w/cpp/language/ub

This depends on what "unpredictable" means. Do I know precisely what this java program will compute? No. But I do know some things that it won't do. Its behavior is not completely unbounded.

That's a really bad standalone definition. It would apply to randomly generating numbers, or most attempts at allocating memory and then sorting by address.