run-command API: make "n" parameter a "size_t"

Make the "n" variable added in c553c72eed (run-command: add an
asynchronous parallel child processor, 2015-12-15) a "size_t". As
we'll see in a subsequent commit we do pass "0" here, but never "jobs
< 0".

We could have made it an "unsigned int", but as we're having to change
this let's not leave another case in the codebase where a size_t and
"unsigned int" size differ on some platforms. In this case it's likely
to never matter, but it's easier to not need to worry about it.

After this and preceding changes:

	make run-command.o DEVOPTS=extra-all CFLAGS=-Wno-unused-parameter

Only has one (and new) -Wsigned-compare warning relevant to a
comparison about our "n" or "{nr,max}_processes": About using our
"n" (size_t) in the same expression as online_cpus() (int). A
subsequent commit will adjust & deal with online_cpus() and that
warning.

The only users of the "n" parameter are:

 * builtin/fetch.c: defaults to 1, reads from the "fetch.parallel"
   config. As seen in the code that parses the config added in
   d54dea77db (fetch: let --jobs=<n> parallelize --multiple, too,
   2019-10-05) will die if the git_config_int() return value is < 0.

   It will however pass us n = 0, as we'll see in a subsequent commit.

 * submodule.c: defaults to 1, reads from "submodule.fetchJobs"
   config. Read via code originally added in a028a1930c (fetching
   submodules: respect `submodule.fetchJobs` config option, 2016-02-29).

   It now piggy-backs on the the submodule.fetchJobs code and
   validation added in f20e7c1ea2 (submodule: remove
   submodule.fetchjobs from submodule-config parsing, 2017-08-02).

   Like builtin/fetch.c it will die if the git_config_int() return
   value is < 0, but like builtin/fetch.c it will pass us n = 0.

 * builtin/submodule--helper.c: defaults to 1. Read via code
   originally added in 2335b870fa (submodule update: expose parallelism
   to the user, 2016-02-29).

   Since f20e7c1ea2 (submodule: remove submodule.fetchjobs from
   submodule-config parsing, 2017-08-02) it shares a config parser and
   semantics with the submodule.c caller.

 * hook.c: hardcoded to 1, see 96e7225b31 (hook: add 'run'
   subcommand, 2021-12-22).

 * t/helper/test-run-command.c: can be -1 after parsing the arguments,
   but will then be overridden to online_cpus() before passing it to
   this API. See be5d88e112 (test-tool run-command: learn to run (parts
   of) the testsuite, 2019-10-04).

Signed-off-by: Ævar Arnfjörð Bjarmason <avarab@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

run-command.c

@@ -1500,8 +1500,8 @@ int run_processes_parallel_ungroup;
 struct parallel_processes {
 	void *data;
 
-	int max_processes;
-	int nr_processes;
+	size_t max_processes;
+	size_t nr_processes;
 
 	get_next_task_fn get_next_task;
 	start_failure_fn start_failure;
@@ -1522,7 +1522,7 @@ struct parallel_processes {
 	unsigned shutdown : 1;
 	unsigned ungroup : 1;
 
-	int output_owner;
+	size_t output_owner;
 	struct strbuf buffered_output; /* of finished children */
 };
 
@@ -1543,9 +1543,7 @@ static int default_task_finished(int result,
 
 static void kill_children(struct parallel_processes *pp, int signo)
 {
-	int i, n = pp->max_processes;
-
-	for (i = 0; i < n; i++)
+	for (size_t i = 0; i < pp->max_processes; i++)
 		if (pp->children[i].state == GIT_CP_WORKING)
 			kill(pp->children[i].process.pid, signo);
 }
@@ -1560,20 +1558,19 @@ static void handle_children_on_signal(int signo)
 }
 
 static void pp_init(struct parallel_processes *pp,
-		    int n,
+		    size_t n,
 		    get_next_task_fn get_next_task,
 		    start_failure_fn start_failure,
 		    task_finished_fn task_finished,
 		    void *data, int ungroup)
 {
-	int i;
-
 	if (n < 1)
 		n = online_cpus();
 
 	pp->max_processes = n;
 
-	trace_printf("run_processes_parallel: preparing to run up to %d tasks", n);
+	trace_printf("run_processes_parallel: preparing to run up to %"PRIuMAX" tasks",
+		     (uintmax_t)n);
 
 	pp->data = data;
 	if (!get_next_task)
@@ -1594,7 +1591,7 @@ static void pp_init(struct parallel_processes *pp,
 		CALLOC_ARRAY(pp->pfd, n);
 	strbuf_init(&pp->buffered_output, 0);
 
-	for (i = 0; i < n; i++) {
+	for (size_t i = 0; i < n; i++) {
 		strbuf_init(&pp->children[i].err, 0);
 		child_process_init(&pp->children[i].process);
 		if (pp->pfd) {
@@ -1609,10 +1606,8 @@ static void pp_init(struct parallel_processes *pp,
 
 static void pp_cleanup(struct parallel_processes *pp)
 {
-	int i;
-
 	trace_printf("run_processes_parallel: done");
-	for (i = 0; i < pp->max_processes; i++) {
+	for (size_t i = 0; i < pp->max_processes; i++) {
 		strbuf_release(&pp->children[i].err);
 		child_process_clear(&pp->children[i].process);
 	}
@@ -1639,7 +1634,8 @@ static void pp_cleanup(struct parallel_processes *pp)
  */
 static int pp_start_one(struct parallel_processes *pp)
 {
-	int i, code;
+	size_t i;
+	int code;
 
 	for (i = 0; i < pp->max_processes; i++)
 		if (pp->children[i].state == GIT_CP_FREE)
@@ -1697,7 +1693,7 @@ static void pp_buffer_stderr(struct parallel_processes *pp, int output_timeout)
 	}
 
 	/* Buffer output from all pipes. */
-	for (i = 0; i < pp->max_processes; i++) {
+	for (size_t i = 0; i < pp->max_processes; i++) {
 		if (pp->children[i].state == GIT_CP_WORKING &&
 		    pp->pfd[i].revents & (POLLIN | POLLHUP)) {
 			int n = strbuf_read_once(&pp->children[i].err,
@@ -1714,7 +1710,7 @@ static void pp_buffer_stderr(struct parallel_processes *pp, int output_timeout)
 
 static void pp_output(struct parallel_processes *pp)
 {
-	int i = pp->output_owner;
+	size_t i = pp->output_owner;
 
 	if (pp->children[i].state == GIT_CP_WORKING &&
 	    pp->children[i].err.len) {
@@ -1725,8 +1721,8 @@ static void pp_output(struct parallel_processes *pp)
 
 static int pp_collect_finished(struct parallel_processes *pp)
 {
-	int i, code;
-	int n = pp->max_processes;
+	int code;
+	size_t i, n = pp->max_processes;
 	int result = 0;
 
 	while (pp->nr_processes > 0) {
@@ -1783,7 +1779,7 @@ static int pp_collect_finished(struct parallel_processes *pp)
 	return result;
 }
 
-void run_processes_parallel(int n,
+void run_processes_parallel(size_t n,
 			    get_next_task_fn get_next_task,
 			    start_failure_fn start_failure,
 			    task_finished_fn task_finished,
@@ -1817,9 +1813,7 @@ void run_processes_parallel(int n,
 		if (!pp.nr_processes)
 			break;
 		if (ungroup) {
-			int i;
-
-			for (i = 0; i < pp.max_processes; i++)
+			for (size_t i = 0; i < pp.max_processes; i++)
 				pp.children[i].state = GIT_CP_WAIT_CLEANUP;
 		} else {
 			pp_buffer_stderr(&pp, output_timeout);
@@ -1836,7 +1830,7 @@ void run_processes_parallel(int n,
 	pp_cleanup(&pp);
 }
 
-void run_processes_parallel_tr2(int n, get_next_task_fn get_next_task,
+void run_processes_parallel_tr2(size_t n, get_next_task_fn get_next_task,
 				start_failure_fn start_failure,
 				task_finished_fn task_finished, void *pp_cb,
 				const char *tr2_category, const char *tr2_label)

run-command.h

@@ -485,12 +485,12 @@ typedef int (*task_finished_fn)(int result,
  * API reads that setting.
  */
 extern int run_processes_parallel_ungroup;
-void run_processes_parallel(int n,
+void run_processes_parallel(size_t n,
 			    get_next_task_fn,
 			    start_failure_fn,
 			    task_finished_fn,
 			    void *pp_cb);
-void run_processes_parallel_tr2(int n, get_next_task_fn, start_failure_fn,
+void run_processes_parallel_tr2(size_t n, get_next_task_fn, start_failure_fn,
 				task_finished_fn, void *pp_cb,
 				const char *tr2_category, const char *tr2_label);