Subject: [PATCH 1/1] builtin/receive-pack: avoid spinning no-op sideband async threads

From: Adrian Ratiu <[email-masked]>
Date: Mon, 2 Mar 2026 21:17:04 +0200

Exit early if the hooks do not exist, to avoid spinning up/down
sideband async threads which no-op.

It is important to call the hook_exists() API provided by hook.[ch]
because it covers both config-defined hooks and the "traditional"
hooks from the hookdir. find_hook() only covers the hookdir hooks.

The regression happened because the no-op async threads add some
additional overhead which can be measured with the receive-refs test
of the benchmarks suite [1].

Reproduced using:
cd benchmarks/receive-refs && \
./run --revisions /path/to/git \
fc148b146ad41be71a7852c4867f0773cbfe1ff9~,fc148b146ad41be71a7852c4867f0773cbfe1ff9 \
--parameter-list refformat reftable --parameter-list refcount 10000

1: https://gitlab.com/gitlab-org/data-access/git/benchmarks

Fixes: fc148b146ad4 ("receive-pack: convert update hooks to new API")
Reported-by: Patrick Steinhardt <[email-masked]>
Helped-by: Jeff King <[email-masked]>
Signed-off-by: Adrian Ratiu <[email-masked]>
---
 builtin/receive-pack.c | 9 +++++++++
 1 file changed, 9 insertions(+)

diff --git a/builtin/receive-pack.c b/builtin/receive-pack.c
index 139a227e71..6376c191c7 100644
--- a/builtin/receive-pack.c
+++ b/builtin/receive-pack.c
@@ -934,6 +934,9 @@ static int run_receive_hook(struct command *commands,
 	int saved_stderr = -1;
 	int ret;
 
+	if (!hook_exists(the_repository, hook_name))
+		return 0;
+
 	/* if there are no valid commands, don't invoke the hook at all. */
 	while (iter && skip_broken && (iter->error_string || iter->did_not_exist))
 		iter = iter->next;
@@ -980,6 +983,9 @@ static int run_update_hook(struct command *cmd)
 	int saved_stderr = -1;
 	int code;
 
+	if (!hook_exists(the_repository, "update"))
+		return 0;
+
 	strvec_pushl(&opt.args,
 		     cmd->ref_name,
 		     oid_to_hex(&cmd->old_oid),
@@ -1674,6 +1680,9 @@ static void run_update_post_hook(struct command *commands)
 	int sideband_async_started = 0;
 	int saved_stderr = -1;
 
+	if (!hook_exists(the_repository, "post-update"))
+		return;
+
 	for (cmd = commands; cmd; cmd = cmd->next) {
 		if (cmd->error_string || cmd->did_not_exist)
 			continue;
-- 
2.52.0.732.gb351b5166d.dirty