are fork.. join statements allowed in functions in system verilog?

Question

they are definitely allowed in tasks, But I could not find, if they are allowed in functions.

Thanks in advance for your help.

Answer 1

Yes, fork...join_none is allowed within functions.

A fork block can only be used in a function if it is matched with a join_none. The reason is that functions must execute in zero time. Because a fork...join_none will be spawned into a separate thread/process, the function can still complete in zero time.

This is clearly stated in IEEE 1800-2012 in section 13.4.4 Background processes spawned by function calls

Functions shall execute with no delay. Thus, a process calling a function shall return immediately. Statements that do not block shall be allowed inside a function; specifically, nonblocking assignments, event triggers, clocking drives, and fork - join_none constructs shall be allowed inside a function.

Answer 2

My simulation tool allows fork...join_none in functions but issues a warning that fork...join (and probably fork...join_any) will be converted to begin...end. I couldn't find anything in the standard about this which most likely is why I don't get a strict compile error.

Be careful as different simulator vendors may implement different rules. In two of the big 3 simulators fork...join_none in functions definitely works. fork...join/join_any doesn't make sense in the context of a function so I would avoid it altogether.