hook: parse the hook.jobs config

The hook.jobs config is a global way to set hook parallelization for
all hooks, in the sense that it is not per-event nor per-hook.

Finer-grained configs will be added in later commits which can override
it, for e.g. via a per-event type job options. Next commits will also
add to this item's documentation.

Parse hook.jobs config key in hook_config_lookup_all() and store its
value in hook_all_config_cb.jobs, then transfer it into
hook_config_cache.jobs after the config pass completes.

This is mostly plumbing and the cached value is not yet used.

Signed-off-by: Adrian Ratiu <adrian.ratiu@collabora.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

Documentation/config/hook.adoc

@@ -22,3 +22,7 @@ hook.<name>.enabled::
 	configuration. This is particularly useful when a hook is defined
 	in a system or global config file and needs to be disabled for a
 	specific repository. See linkgit:git-hook[1].
+
+hook.jobs::
+	Specifies how many hooks can be run simultaneously during parallelized
+	hook execution. If unspecified, defaults to 1 (serial execution).

hook.c

@@ -132,11 +132,13 @@ struct hook_config_cache_entry {
  * commands: friendly-name to command map.
  * event_hooks: event-name to list of friendly-names map.
  * disabled_hooks: set of friendly-names with hook.name.enabled = false.
+ * jobs: value of the global hook.jobs key. Defaults to 0 if unset.
  */
 struct hook_all_config_cb {
 	struct strmap commands;
 	struct strmap event_hooks;
 	struct string_list disabled_hooks;
+	unsigned int jobs;
 };
 
 /* repo_config() callback that collects all hook.* configuration in one pass. */
@@ -152,6 +154,20 @@ static int hook_config_lookup_all(const char *key, const char *value,
 	if (parse_config_key(key, "hook", &name, &name_len, &subkey))
 		return 0;
 
+	/* Handle plain hook.<key> entries that have no hook name component. */
+	if (!name) {
+		if (!strcmp(subkey, "jobs") && value) {
+			unsigned int v;
+			if (!git_parse_uint(value, &v))
+				warning(_("hook.jobs must be a positive integer, ignoring: '%s'"), value);
+			else if (!v)
+				warning(_("hook.jobs must be positive, ignoring: 0"));
+			else
+				data->jobs = v;
+		}
+		return 0;
+	}
+
 	if (!value)
 		return config_error_nonbool(key);
 
@@ -236,7 +252,7 @@ void hook_cache_clear(struct hook_config_cache *cache)
 static void build_hook_config_map(struct repository *r,
 				  struct hook_config_cache *cache)
 {
-	struct hook_all_config_cb cb_data;
+	struct hook_all_config_cb cb_data = { 0 };
 	struct hashmap_iter iter;
 	struct strmap_entry *e;
 
@@ -244,7 +260,7 @@ static void build_hook_config_map(struct repository *r,
 	strmap_init(&cb_data.event_hooks);
 	string_list_init_dup(&cb_data.disabled_hooks);
 
-	/* Parse all configs in one run. */
+	/* Parse all configs in one run, capturing hook.* including hook.jobs. */
 	repo_config(r, hook_config_lookup_all, &cb_data);
 
 	/* Construct the cache from parsed configs. */
@@ -279,6 +295,8 @@ static void build_hook_config_map(struct repository *r,
 		strmap_put(&cache->hooks, e->key, hooks);
 	}
 
+	cache->jobs = cb_data.jobs;
+
 	strmap_clear(&cb_data.commands, 1);
 	string_list_clear(&cb_data.disabled_hooks, 0);
 	strmap_for_each_entry(&cb_data.event_hooks, &iter, e) {

hook.h

@@ -197,6 +197,7 @@ void hook_list_clear(struct string_list *hooks, cb_data_free_fn cb_data_free);
  */
 struct hook_config_cache {
 	struct strmap hooks; /* maps event name -> string_list of hooks */
+	unsigned int jobs; /* hook.jobs config value; 0 if unset (defaults to serial) */
 };
 
 /**