Stefan Beller <sbeller@xxxxxxxxxx> writes:
> +void default_start_failure(void *data,
> + struct child_process *cp,
> + struct strbuf *err)
> +{
> + int i;
> + struct strbuf sb = STRBUF_INIT;
> +
> + for (i = 0; cp->argv[i]; i++)
> + strbuf_addf(&sb, "%s ", cp->argv[i]);
> + die_errno("Starting a child failed:\n%s", sb.buf);
Do we want that trailing SP after the last element of argv[]?
Same question applies to the one in "return-value".
> +static void run_processes_parallel_init(struct parallel_processes *pp,
> + int n, void *data,
> + get_next_task_fn get_next_task,
> + start_failure_fn start_failure,
> + return_value_fn return_value)
> +{
> + int i;
> +
> + if (n < 1)
> + n = online_cpus();
> +
> + pp->max_processes = n;
> + pp->data = data;
> + if (!get_next_task)
> + die("BUG: you need to specify a get_next_task function");
> + pp->get_next_task = get_next_task;
> +
> + pp->start_failure = start_failure ? start_failure : default_start_failure;
> + pp->return_value = return_value ? return_value : default_return_value;
I would actually have expected that leaving these to NULL will just
skip pp->fn calls, instead of a "default implementation", but a pair
of very simple default implementation would not hrtut.
> +static void run_processes_parallel_cleanup(struct parallel_processes *pp)
> +{
> + int i;
Have a blank between the decl block and the first stmt here (and
elsewhere, too---which you got correct in the function above)?
> + for (i = 0; i < pp->max_processes; i++)
> + strbuf_release(&pp->children[i].err);
> +static void run_processes_parallel_start_one(struct parallel_processes *pp)
> +{
> + int i;
> +
> + for (i = 0; i < pp->max_processes; i++)
> + if (!pp->children[i].in_use)
> + break;
> + if (i == pp->max_processes)
> + die("BUG: bookkeeping is hard");
Mental note: the caller is responsible for not calling this when all
slots are taken.
> + if (!pp->get_next_task(pp->data,
> + &pp->children[i].process,
> + &pp->children[i].err)) {
> + pp->all_tasks_started = 1;
> + return;
> + }
Mental note: but it is OK to call this if get_next_task() previously
said "no more task".
The above two shows a slight discrepancy (nothing earth-breaking).
I have this suspicion that the all-tasks-started bit may turn out to
be a big mistake that we may later regret. Don't we want to allow
pp->more_task() to say "no more task to run at this moment" implying
"but please do ask me later, because I may have found more to do by
the time you ask me again"?
That is one of the reasons why I do not think the "very top level is
a bulleted list" organization is a good idea in general. A good
scheduling decision can seldom be made in isolation without taking
global picture into account.
> +static void run_processes_parallel_collect_finished(struct parallel_processes *pp)
> +{
> + int i = 0;
> + pid_t pid;
> + int wait_status, code;
> + int n = pp->max_processes;
> +
> + while (pp->nr_processes > 0) {
> + pid = waitpid(-1, &wait_status, WNOHANG);
> + if (pid == 0)
> + return;
> +
> + if (pid < 0)
> + die_errno("wait");
> +
> + for (i = 0; i < pp->max_processes; i++)
> + if (pp->children[i].in_use &&
> + pid == pp->children[i].process.pid)
> + break;
> + if (i == pp->max_processes)
> + /*
> + * waitpid returned another process id
> + * which we are not waiting for.
> + */
> + return;
If we culled a child process that this machinery is not in charge
of, waitpid() in other places that wants to see that child will not
see it. Perhaps such a situation might even warrant an error() or
BUG()? Do we want a "NEEDSWORK: Is this a bug?" comment here at
least?
> + if (strbuf_read_once(&pp->children[i].err,
> + pp->children[i].process.err, 0) < 0 &&
> + errno != EAGAIN)
> + die_errno("strbuf_read_once");
Don't we want to read thru to the end here? The reason read_once()
did not read thru to the end may not have anything to do with
NONBLOCK (e.g. xread_nonblock() caps len, and it does not loop).
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