Re: [PATCH v3 15/15] run-command.c: remove "max_processes", add "const" to signal() handler

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Ævar Arnfjörð Bjarmason         <avarab@xxxxxxxxx> writes:

> In this case we need the number of processes for the kill_children()
> function, which will be called from a signal handler. To do that
> adjust this code added in c553c72eed6 (run-command: add an
> asynchronous parallel child processor, 2015-12-15) so that we use a
> dedicated "struct parallel_processes_for_signal" for passing data to
> the signal handler, in addition to the "struct parallel_process" it'll
> now have access to our "opts" variable.

[...]

> -static void kill_children(const struct parallel_processes *pp, int signo)
> +struct parallel_processes_for_signal {
> +	const struct run_process_parallel_opts *opts;
> +	const struct parallel_processes *pp;
> +};

(Treat this feedback as non-blocking)

I find this struct a little odd because it isn't specific to
kill_children_signal(), rather, this seems like we are saying that
"run_process_parallel_opts" and "parallel_processes" belong together.
This also seems confirmed by the fact that at the end of the series, we
pass the opts almost everywhere - only pp_output() takes
"parallel_processes" without "run_process_parallel_opts".

I assume you've already considered this, but I wonder if the code is
simpler if we drop 10-15/15, i.e. use options just for end users
(allowing us to get rid of the *_tr2() variant too, which is great), but
only use "parallel_processes" inside of run-command.c. There's also a
tiny benefit of passing one fewer pointer per function, with the tiny
cost of one-time copying.

Thoughts?

> +
> +static void kill_children(const struct parallel_processes *pp,
> +			  const struct run_process_parallel_opts *opts,
> +			  int signo)
>  {
> -	for (size_t i = 0; i < pp->max_processes; i++)
> +	for (size_t i = 0; i < opts->processes; i++)
>  		if (pp->children[i].state == GIT_CP_WORKING)
>  			kill(pp->children[i].process.pid, signo);
>  }
>  
> -static struct parallel_processes *pp_for_signal;
> +static void kill_children_signal(const struct parallel_processes_for_signal *pp_sig,
> +				 int signo)
> +{
> +	kill_children(pp_sig->pp, pp_sig->opts, signo);
> +}
> +
> +static struct parallel_processes_for_signal *pp_for_signal;
>  
>  static void handle_children_on_signal(int signo)
>  {
> -	kill_children(pp_for_signal, signo);
> +	kill_children_signal(pp_for_signal, signo);
>  	sigchain_pop(signo);
>  	raise(signo);
>  }
>  
>  static void pp_init(struct parallel_processes *pp,
> -		    const struct run_process_parallel_opts *opts)
> +		    const struct run_process_parallel_opts *opts,
> +		    struct parallel_processes_for_signal *pp_sig)
>  {
>  	const size_t n = opts->processes;
>  
> @@ -1561,7 +1574,9 @@ static void pp_init(struct parallel_processes *pp,
>  		}
>  	}
>  
> -	pp_for_signal = pp;
> +	pp_sig->pp = pp;
> +	pp_sig->opts = opts;
> +	pp_for_signal = pp_sig;
>  	sigchain_push_common(handle_children_on_signal);
>  }
>  
> @@ -1759,8 +1774,8 @@ void run_processes_parallel(const struct run_process_parallel_opts *opts)
>  	int i, code;
>  	int output_timeout = 100;
>  	int spawn_cap = 4;
> +	struct parallel_processes_for_signal pp_sig;
>  	struct parallel_processes pp = {
> -		.max_processes = opts->processes,
>  		.buffered_output = STRBUF_INIT,
>  	};
>  	/* options */
> @@ -1772,7 +1787,7 @@ void run_processes_parallel(const struct run_process_parallel_opts *opts)
>  		trace2_region_enter_printf(tr2_category, tr2_label, NULL,
>  					   "max:%d", opts->processes);
>  
> -	pp_init(&pp, opts);
> +	pp_init(&pp, opts, &pp_sig);
>  	while (1) {
>  		for (i = 0;
>  		    i < spawn_cap && !pp.shutdown &&
> @@ -1783,7 +1798,7 @@ void run_processes_parallel(const struct run_process_parallel_opts *opts)
>  				continue;
>  			if (code < 0) {
>  				pp.shutdown = 1;
> -				kill_children(&pp, -code);
> +				kill_children(&pp, opts, -code);
>  			}
>  			break;
>  		}
> @@ -1800,7 +1815,7 @@ void run_processes_parallel(const struct run_process_parallel_opts *opts)
>  		if (code) {
>  			pp.shutdown = 1;
>  			if (code < 0)
> -				kill_children(&pp, -code);
> +				kill_children(&pp, opts,-code);
>  		}
>  	}
>  
> -- 
> 2.38.0.971.ge79ff6d20e7




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