hook: mark non-parallelizable hooks
Several hooks are known to be inherently non-parallelizable, so initialize them with RUN_HOOKS_OPT_INIT_FORCE_SERIAL. This pins jobs=1 and overrides any hook.jobs or runtime -j flags. These hooks are: applypatch-msg, pre-commit, prepare-commit-msg, commit-msg, post-commit, post-checkout, and push-to-checkout. Signed-off-by: Emily Shaffer <emilyshaffer@google.com> Signed-off-by: Adrian Ratiu <adrian.ratiu@collabora.com> Signed-off-by: Junio C Hamano <gitster@pobox.com>
Emily Shaffer committed
Apr 10, 2026 at 12:06 UTC
ae25764e50f38b6625e11c3a7d7de290a0075b9c
8 files changed
+56
-14
Documentation/config/hook.adoc
+14
index 94c7a9808e..6f60775c28 100644
--- a/Documentation/config/hook.adoc
+++ b/Documentation/config/hook.adoc
@@ -36,6 +36,20 @@ hook.<friendly-name>.parallel::
hook.jobs::
Specifies how many hooks can be run simultaneously during parallelized
hook execution. If unspecified, defaults to 1 (serial execution).
+ Some hooks always run sequentially regardless of this setting because
+ they operate on shared data and cannot safely be parallelized:
++
+--
+`applypatch-msg`;;
+`prepare-commit-msg`;;
+`commit-msg`;;
+ Receive a commit message file and may rewrite it in place.
+`pre-commit`;;
+`post-checkout`;;
+`push-to-checkout`;;
+`post-commit`;;
+ Access the working tree, index, or repository state.
+--
+
This setting has no effect unless all configured hooks for the event have
`hook.<friendly-name>.parallel` set to `true`.
builtin/am.c
+5
-3
index fe6e087eee..e9623b8307 100644
--- a/builtin/am.c
+++ b/builtin/am.c
@@ -490,9 +490,11 @@ static int run_applypatch_msg_hook(struct am_state *state)
assert(state->msg);
- if (!state->no_verify)
- ret = run_hooks_l(the_repository, "applypatch-msg",
- am_path(state, "final-commit"), NULL);
+ if (!state->no_verify) {
+ struct run_hooks_opt opt = RUN_HOOKS_OPT_INIT_FORCE_SERIAL;
+ strvec_push(&opt.args, am_path(state, "final-commit"));
+ ret = run_hooks_opt(the_repository, "applypatch-msg", &opt);
+ }
if (!ret) {
FREE_AND_NULL(state->msg);
builtin/checkout.c
+13
-6
index e031e61886..ac0186a33e 100644
--- a/builtin/checkout.c
+++ b/builtin/checkout.c
@@ -31,6 +31,7 @@
#include "resolve-undo.h"
#include "revision.h"
#include "setup.h"
+#include "strvec.h"
#include "submodule.h"
#include "symlinks.h"
#include "trace2.h"
@@ -123,13 +124,19 @@ static void branch_info_release(struct branch_info *info)
static int post_checkout_hook(struct commit *old_commit, struct commit *new_commit,
int changed)
{
- return run_hooks_l(the_repository, "post-checkout",
- oid_to_hex(old_commit ? &old_commit->object.oid : null_oid(the_hash_algo)),
- oid_to_hex(new_commit ? &new_commit->object.oid : null_oid(the_hash_algo)),
- changed ? "1" : "0", NULL);
- /* "new_commit" can be NULL when checking out from the index before
- a commit exists. */
+ struct run_hooks_opt opt = RUN_HOOKS_OPT_INIT_FORCE_SERIAL;
+ /*
+ * "new_commit" can be NULL when checking out from the index before
+ * a commit exists.
+ */
+ strvec_pushl(&opt.args,
+ oid_to_hex(old_commit ? &old_commit->object.oid : null_oid(the_hash_algo)),
+ oid_to_hex(new_commit ? &new_commit->object.oid : null_oid(the_hash_algo)),
+ changed ? "1" : "0",
+ NULL);
+
+ return run_hooks_opt(the_repository, "post-checkout", &opt);
}
static int update_some(const struct object_id *oid, struct strbuf *base,
builtin/clone.c
+4
-2
index fba3c9c508..d23b0cafcf 100644
--- a/builtin/clone.c
+++ b/builtin/clone.c
@@ -647,6 +647,7 @@ static int checkout(int submodule_progress,
struct tree *tree;
struct tree_desc t;
int err = 0;
+ struct run_hooks_opt hook_opt = RUN_HOOKS_OPT_INIT_FORCE_SERIAL;
if (option_no_checkout)
return 0;
@@ -697,8 +698,9 @@ static int checkout(int submodule_progress,
if (write_locked_index(the_repository->index, &lock_file, COMMIT_LOCK))
die(_("unable to write new index file"));
- err |= run_hooks_l(the_repository, "post-checkout", oid_to_hex(null_oid(the_hash_algo)),
- oid_to_hex(&oid), "1", NULL);
+ strvec_pushl(&hook_opt.args, oid_to_hex(null_oid(the_hash_algo)),
+ oid_to_hex(&oid), "1", NULL);
+ err |= run_hooks_opt(the_repository, "post-checkout", &hook_opt);
if (!err && (option_recurse_submodules.nr > 0)) {
struct child_process cmd = CHILD_PROCESS_INIT;
builtin/receive-pack.c
+2
-1
index dada55884a..6da60f640c 100644
--- a/builtin/receive-pack.c
+++ b/builtin/receive-pack.c
@@ -1455,7 +1455,8 @@ static const char *push_to_checkout(unsigned char *hash,
struct strvec *env,
const char *work_tree)
{
- struct run_hooks_opt opt = RUN_HOOKS_OPT_INIT;
+ struct run_hooks_opt opt = RUN_HOOKS_OPT_INIT_FORCE_SERIAL;
+
opt.invoked_hook = invoked_hook;
strvec_pushf(env, "GIT_WORK_TREE=%s", absolute_path(work_tree));
builtin/worktree.c
+1
-1
index 4fd6f7575f..d21c43fde3 100644
--- a/builtin/worktree.c
+++ b/builtin/worktree.c
@@ -609,7 +609,7 @@ done:
* is_junk is cleared, but do return appropriate code when hook fails.
*/
if (!ret && opts->checkout && !opts->orphan) {
- struct run_hooks_opt opt = RUN_HOOKS_OPT_INIT;
+ struct run_hooks_opt opt = RUN_HOOKS_OPT_INIT_FORCE_SERIAL;
strvec_pushl(&opt.env, "GIT_DIR", "GIT_WORK_TREE", NULL);
strvec_pushl(&opt.args,
commit.c
+1
-1
index 80d8d07875..4385ae4329 100644
--- a/commit.c
+++ b/commit.c
@@ -1970,7 +1970,7 @@ size_t ignored_log_message_bytes(const char *buf, size_t len)
int run_commit_hook(int editor_is_used, const char *index_file,
int *invoked_hook, const char *name, ...)
{
- struct run_hooks_opt opt = RUN_HOOKS_OPT_INIT;
+ struct run_hooks_opt opt = RUN_HOOKS_OPT_INIT_FORCE_SERIAL;
va_list args;
const char *arg;
t/t1800-hook.sh
+16
index 4a978aff5e..63fa25bca2 100755
--- a/t/t1800-hook.sh
+++ b/t/t1800-hook.sh
@@ -832,4 +832,20 @@ test_expect_success 'client hooks: pre-push runs in parallel when hook.jobs > 1'
test_cmp expect repo-parallel/hook.order
'
+test_expect_success 'hook.jobs=2 is ignored for force-serial hooks (pre-commit)' '
+ test_when_finished "rm -f sentinel.started sentinel.done hook.order" &&
+ test_config hook.hook-1.event pre-commit &&
+ test_config hook.hook-1.command \
+ "touch sentinel.started; sleep 2; touch sentinel.done" &&
+ test_config hook.hook-1.parallel true &&
+ test_config hook.hook-2.event pre-commit &&
+ test_config hook.hook-2.command \
+ "$(sentinel_detector sentinel hook.order)" &&
+ test_config hook.hook-2.parallel true &&
+ test_config hook.jobs 2 &&
+ git commit --allow-empty -m "test: verify force-serial on pre-commit" &&
+ echo serial >expect &&
+ test_cmp expect hook.order
+'
+
test_done