[PATCH v3 07/15] run-command API: have run_process_parallel() take an "opts" struct

["Ævar Arnfjörð Bjarmason" <avarab@gmail.com>]

As noted in fd3aaf53f71 (run-command: add an "ungroup" option to
run_process_parallel(), 2022-06-07) which added the "ungroup" passing
it to "run_process_parallel()" via the global
"run_processes_parallel_ungroup" variable was a compromise to get the
smallest possible regression fix for "maint" at the time.

This follow-up to that is a start at passing that parameter and others
via a new "struct run_process_parallel_opts", as the earlier
version[1] of what became fd3aaf53f71 did.

Since we need to change all of the occurrences of "n" to
"opt->SOMETHING" let's take the opportunity and rename the terse "n"
to "processes". We could also have picked "max_processes", "jobs",
"threads" etc., but as the API is named "run_processes_parallel()"
let's go with "processes".

Since the new "run_processes_parallel()" function is able to take an
optional "tr2_category" and "tr2_label" via the struct we can at this
point migrate all of the users of "run_processes_parallel_tr2()" over
to it.

But let's not migrate all the API users yet, only the two users that
passed the "ungroup" parameter via the
"run_processes_parallel_ungroup" global

1. https://lore.kernel.org/git/cover-v2-0.8-00000000000-20220518T195858Z-avarab@gmail.com/

Signed-off-by: Ævar Arnfjörð Bjarmason <avarab@gmail.com>
---
 hook.c                      | 23 +++++++-----
 run-command.c               | 54 ++++++++++++++++------------
 run-command.h               | 72 ++++++++++++++++++++++++++++---------
 t/helper/test-run-command.c | 31 ++++++++++------
 4 files changed, 121 insertions(+), 59 deletions(-)

diff --git a/hook.c b/hook.c
index a493939a4fc..a4fa1031f28 100644
--- a/hook.c
+++ b/hook.c
@@ -114,8 +114,20 @@ int run_hooks_opt(const char *hook_name, struct run_hooks_opt *options)
 		.options = options,
 	};
 	const char *const hook_path = find_hook(hook_name);
-	int jobs = 1;
 	int ret = 0;
+	const struct run_process_parallel_opts opts = {
+		.tr2_category = "hook",
+		.tr2_label = hook_name,
+
+		.processes = 1,
+		.ungroup = 1,
+
+		.get_next_task = pick_next_hook,
+		.start_failure = notify_start_failure,
+		.task_finished = notify_hook_finished,
+
+		.data = &cb_data,
+	};
 
 	if (!options)
 		BUG("a struct run_hooks_opt must be provided to run_hooks");
@@ -137,14 +149,7 @@ int run_hooks_opt(const char *hook_name, struct run_hooks_opt *options)
 		cb_data.hook_path = abs_path.buf;
 	}
 
-	run_processes_parallel_ungroup = 1;
-	run_processes_parallel_tr2(jobs,
-				   pick_next_hook,
-				   notify_start_failure,
-				   notify_hook_finished,
-				   &cb_data,
-				   "hook",
-				   hook_name);
+	run_processes_parallel(&opts);
 	ret = cb_data.rc;
 cleanup:
 	strbuf_release(&abs_path);
diff --git a/run-command.c b/run-command.c
index b69deb1cc53..2858ec7bef5 100644
--- a/run-command.c
+++ b/run-command.c
@@ -1496,7 +1496,6 @@ enum child_state {
 	GIT_CP_WAIT_CLEANUP,
 };
 
-int run_processes_parallel_ungroup;
 struct parallel_processes {
 	void *const data;
 
@@ -1558,11 +1557,12 @@ static void handle_children_on_signal(int signo)
 }
 
 static void pp_init(struct parallel_processes *pp,
-		    get_next_task_fn get_next_task,
-		    start_failure_fn start_failure,
-		    task_finished_fn task_finished)
+		    const struct run_process_parallel_opts *opts)
 {
-	const size_t n = pp->max_processes;
+	const size_t n = opts->processes;
+	get_next_task_fn get_next_task = opts->get_next_task;
+	start_failure_fn start_failure = opts->start_failure;
+	task_finished_fn task_finished = opts->task_finished;
 
 	if (!n)
 		BUG("you must provide a non-zero number of processes!");
@@ -1769,27 +1769,27 @@ static int pp_collect_finished(struct parallel_processes *pp)
 	return result;
 }
 
-void run_processes_parallel(size_t n,
-			    get_next_task_fn get_next_task,
-			    start_failure_fn start_failure,
-			    task_finished_fn task_finished,
-			    void *pp_cb)
+void run_processes_parallel(const struct run_process_parallel_opts *opts)
 {
 	int i, code;
 	int output_timeout = 100;
 	int spawn_cap = 4;
-	int ungroup = run_processes_parallel_ungroup;
 	struct parallel_processes pp = {
-		.max_processes = n,
-		.data = pp_cb,
+		.max_processes = opts->processes,
+		.data = opts->data,
 		.buffered_output = STRBUF_INIT,
-		.ungroup = ungroup,
+		.ungroup = opts->ungroup,
 	};
+	/* options */
+	const char *tr2_category = opts->tr2_category;
+	const char *tr2_label = opts->tr2_label;
+	const int do_trace2 = tr2_category && tr2_label;
 
-	/* unset for the next API user */
-	run_processes_parallel_ungroup = 0;
+	if (do_trace2)
+		trace2_region_enter_printf(tr2_category, tr2_label, NULL,
+					   "max:%d", opts->processes);
 
-	pp_init(&pp, get_next_task, start_failure, task_finished);
+	pp_init(&pp, opts);
 	while (1) {
 		for (i = 0;
 		    i < spawn_cap && !pp.shutdown &&
@@ -1806,7 +1806,7 @@ void run_processes_parallel(size_t n,
 		}
 		if (!pp.nr_processes)
 			break;
-		if (ungroup) {
+		if (opts->ungroup) {
 			for (size_t i = 0; i < pp.max_processes; i++)
 				pp.children[i].state = GIT_CP_WAIT_CLEANUP;
 		} else {
@@ -1822,19 +1822,27 @@ void run_processes_parallel(size_t n,
 	}
 
 	pp_cleanup(&pp);
+
+	if (do_trace2)
+		trace2_region_leave(tr2_category, tr2_label, NULL);
 }
 
-void run_processes_parallel_tr2(size_t n, get_next_task_fn get_next_task,
+void run_processes_parallel_tr2(size_t processes, 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)
 {
-	trace2_region_enter_printf(tr2_category, tr2_label, NULL, "max:%d", n);
+	const struct run_process_parallel_opts opts = {
+		.tr2_category = tr2_category,
+		.tr2_label = tr2_label,
+		.processes = processes,
 
-	run_processes_parallel(n, get_next_task, start_failure,
-			       task_finished, pp_cb);
+		.get_next_task = get_next_task,
+		.start_failure = start_failure,
+		.task_finished = task_finished,
+	};
 
-	trace2_region_leave(tr2_category, tr2_label, NULL);
+	run_processes_parallel(&opts);
 }
 
 int run_auto_maintenance(int quiet)
diff --git a/run-command.h b/run-command.h
index 6f7604e1146..aabdaf684db 100644
--- a/run-command.h
+++ b/run-command.h
@@ -459,17 +459,64 @@ typedef int (*task_finished_fn)(int result,
 				void *pp_task_cb);
 
 /**
- * Runs up to n processes at the same time. Whenever a process can be
- * started, the callback get_next_task_fn is called to obtain the data
+ * Option used by run_processes_parallel(), { 0 }-initialized means no
+ * options.
+ */
+struct run_process_parallel_opts
+{
+	/**
+	 * tr2_category & tr2_label: sets the trace2 category and label for
+	 * logging. These must either be unset, or both of them must be set.
+	 */
+	const char *tr2_category;
+	const char *tr2_label;
+
+	/**
+	 * processes: see 'processes' in run_processes_parallel() below.
+	 */
+	size_t processes;
+
+	/**
+	 * ungroup: see 'ungroup' in run_processes_parallel() below.
+	 */
+	unsigned int ungroup:1;
+
+	/**
+	 * get_next_task: See get_next_task_fn() above. This must be
+	 * specified.
+	 */
+	get_next_task_fn get_next_task;
+
+	/**
+	 * start_failure: See start_failure_fn() above. This can be
+	 * NULL to omit any special handling.
+	 */
+	start_failure_fn start_failure;
+
+	/**
+	 * task_finished: See task_finished_fn() above. This can be
+	 * NULL to omit any special handling.
+	 */
+	task_finished_fn task_finished;
+
+	/**
+	 * data: user data, will be passed as "pp_cb" to the callback
+	 * parameters.
+	 */
+	void *data;
+};
+
+/**
+ * Options are passed via the "struct run_process_parallel_opts" above.
+ *
+ * Runs N 'processes' at the same time. Whenever a process can be
+ * started, the callback opts.get_next_task is called to obtain the data
  * required to start another child process.
  *
  * The children started via this function run in parallel. Their output
  * (both stdout and stderr) is routed to stderr in a manner that output
  * from different tasks does not interleave (but see "ungroup" below).
  *
- * start_failure_fn and task_finished_fn can be NULL to omit any
- * special handling.
- *
  * If the "ungroup" option isn't specified, the API will set the
  * "stdout_to_stderr" parameter in "struct child_process" and provide
  * the callbacks with a "struct strbuf *out" parameter to write output
@@ -479,19 +526,10 @@ typedef int (*task_finished_fn)(int result,
  * NULL "struct strbuf *out" parameter, and are responsible for
  * emitting their own output, including dealing with any race
  * conditions due to writing in parallel to stdout and stderr.
- * The "ungroup" option can be enabled by setting the global
- * "run_processes_parallel_ungroup" to "1" before invoking
- * run_processes_parallel(), it will be set back to "0" as soon as the
- * API reads that setting.
  */
-extern int run_processes_parallel_ungroup;
-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(size_t n, get_next_task_fn, start_failure_fn,
-				task_finished_fn, void *pp_cb,
+void run_processes_parallel(const struct run_process_parallel_opts *opts);
+void run_processes_parallel_tr2(size_t processes, get_next_task_fn,
+				start_failure_fn, task_finished_fn, void *pp_cb,
 				const char *tr2_category, const char *tr2_label);
 
 /**
diff --git a/t/helper/test-run-command.c b/t/helper/test-run-command.c
index ee509aefa2f..3ecb830f4a8 100644
--- a/t/helper/test-run-command.c
+++ b/t/helper/test-run-command.c
@@ -136,7 +136,7 @@ static const char * const testsuite_usage[] = {
 static int testsuite(int argc, const char **argv)
 {
 	struct testsuite suite = TESTSUITE_INIT;
-	int max_jobs = 1, i, ret;
+	int max_jobs = 1, i, ret = 0;
 	DIR *dir;
 	struct dirent *d;
 	struct option options[] = {
@@ -152,6 +152,12 @@ static int testsuite(int argc, const char **argv)
 			 "write JUnit-style XML files"),
 		OPT_END()
 	};
+	struct run_process_parallel_opts opts = {
+		.get_next_task = next_test,
+		.start_failure = test_failed,
+		.task_finished = test_finished,
+		.data = &suite,
+	};
 
 	argc = parse_options(argc, argv, NULL, options,
 			testsuite_usage, PARSE_OPT_STOP_AT_NON_OPTION);
@@ -192,8 +198,8 @@ static int testsuite(int argc, const char **argv)
 	fprintf(stderr, "Running %"PRIuMAX" tests (%d at a time)\n",
 		(uintmax_t)suite.tests.nr, max_jobs);
 
-	run_processes_parallel(max_jobs, next_test, test_failed,
-			       test_finished, &suite);
+	opts.processes = max_jobs;
+	run_processes_parallel(&opts);
 
 	if (suite.failed.nr > 0) {
 		ret = 1;
@@ -206,7 +212,7 @@ static int testsuite(int argc, const char **argv)
 	string_list_clear(&suite.tests, 0);
 	string_list_clear(&suite.failed, 0);
 
-	return !!ret;
+	return ret;
 }
 
 static uint64_t my_random_next = 1234;
@@ -382,6 +388,9 @@ int cmd__run_command(int argc, const char **argv)
 	struct child_process proc = CHILD_PROCESS_INIT;
 	int jobs;
 	int ret;
+	struct run_process_parallel_opts opts = {
+		.data = &proc,
+	};
 
 	if (argc > 1 && !strcmp(argv[1], "testsuite"))
 		return testsuite(argc - 1, argv + 1);
@@ -427,7 +436,7 @@ int cmd__run_command(int argc, const char **argv)
 	if (!strcmp(argv[1], "--ungroup")) {
 		argv += 1;
 		argc -= 1;
-		run_processes_parallel_ungroup = 1;
+		opts.ungroup = 1;
 	}
 
 	jobs = atoi(argv[2]);
@@ -435,18 +444,20 @@ int cmd__run_command(int argc, const char **argv)
 	strvec_pushv(&proc.args, (const char **)argv + 3);
 
 	if (!strcmp(argv[1], "run-command-parallel")) {
-		run_processes_parallel(jobs, parallel_next, NULL, NULL, &proc);
+		opts.get_next_task = parallel_next;
 	} else if (!strcmp(argv[1], "run-command-abort")) {
-		run_processes_parallel(jobs, parallel_next, NULL,
-				       task_finished, &proc);
+		opts.get_next_task = parallel_next;
+		opts.task_finished = task_finished;
 	} else if (!strcmp(argv[1], "run-command-no-jobs")) {
-		run_processes_parallel(jobs, no_job, NULL, task_finished,
-				       &proc);
+		opts.get_next_task = no_job;
+		opts.task_finished = task_finished;
 	} else {
 		ret = 1;
 		fprintf(stderr, "check usage\n");
 		goto cleanup;
 	}
+	opts.processes = jobs;
+	run_processes_parallel(&opts);
 	ret = 0;
 cleanup:
 	child_process_clear(&proc);
-- 
2.38.0.971.ge79ff6d20e7