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Fork a task with parameter from within a function

Jeff000

Hi,

Below is what I've tried to start a task with parameter from a function.


function fork_task_in_func()
	for (int i = O; i < 3; i++) begin
		fork
		  print_me(i);
		join_none
	end
endfunction

task print_me(int i);
	$display("print me: i: %Od\n", i);
endtask

What I expect is as follows,

print me: i: 0
print me: i: 1
print me: i: 2

But the actual outputs are,

print me: i: 3
print me: i: 3
print me: i: 3

Anyone can explain a bit for this result?

Thanks.

  • The forked threads are not started until the join_none is reached, meaning that when the threads start the for loop has finished and i == 3. The LRM explains this in some detail, and shows the correct way to do it using an automatic variable. This automatic variable works because the initialiser takes effect instantly rather than waiting till the thread starts.

    for (int i=0; i<3; i++) begin : loop

    fork

    automatic int ii = i;

    begin

    print_me(ii);

    end

    join_none

    end : loop

  • in reply to StephenH

    Thanks.

    If the forked threads won't get started until the end of the for loop, then the automatic ii will still be assigned with the i == 3, right?

    I've tried as your suggestion but still have the following output,

    print me: i: 3
    print me: i: 3
    print me: i: 3

  • in reply to Jeff000

    My apologies, I replied before my morning coffee and got the automatic variable in the wrong place, I've updated my post to show the correct code. See also the end of section 9.3.2 in the 2012 LRM.

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