Re: [PATCH] run_processes_parallel: change confusing task_cb convention

> By declaring the task_cb parameter of type `void **`, the signature of
> the get_next_task method suggests that the "task-specific cookie" can be
> defined in that method, and the signatures of the start_failure and of
> the task_finished methods declare that parameter of type `void *`,
> suggesting that those methods are mere users of said cookie.
>
> That convention makes a total lot of sense, because the tasks are pretty
> much dead when one of the latter two methods is called: there would be
> little use to reset that cookie at that point because nobody would be
> able to see the change afterwards.
>
> However, this is not what the code actually does. For all three methods,
> it passes the *address* of pp->children[i].data.
>
> As reasoned above, this behavior makes no sense. So let's change the
> implementation to adhere to the convention suggested by the signatures.
>
> Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>