Re: [PATCH] maintenance: compare output of pthread functions for inequality with 0

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

On Fri, Dec 02 2022, Rose via GitGitGadget wrote:

> From: Seija <doremylover123@gmail.com>
>
> The documentation for pthread_create and pthread_sigmask state that:
>
> "On success, pthread_create() returns 0;
> on error, it returns an error number"
>
> As such, we ought to check for an error
> by seeing if the output is not 0.
>
> Checking for "less than" is a mistake
> as the error code numbers can be greater than 0.
>
> Signed-off-by: Seija <doremylover123@gmail.com>
> ---
>     maintenance: compare output of pthread functions for inequality with 0
>     
>     The documentation for pthread_create and pthread_sigmask state that "On
>     success, pthread_create() returns 0; on error, it returns an error
>     number, and the contents of *thread are undefined."
>     
>     As such, we ought to check for an error by seeing if the output is not
>     0, rather than being less than 0, since nothing stops these functions
>     from returning a positive number.
>     
>     Signed-off by: Seija doremylover123@gmail.com
>
> Published-As: https://github.com/gitgitgadget/git/releases/tag/pr-git-1389%2FAtariDreams%2Faddress-v1
> Fetch-It-Via: git fetch https://github.com/gitgitgadget/git pr-git-1389/AtariDreams/address-v1
> Pull-Request: https://github.com/git/git/pull/1389
>
>  builtin/fsmonitor--daemon.c | 4 ++--
>  run-command.c               | 2 +-
>  2 files changed, 3 insertions(+), 3 deletions(-)
>
> diff --git a/builtin/fsmonitor--daemon.c b/builtin/fsmonitor--daemon.c
> index 6f30a4f93a7..52a08bb3b57 100644
> --- a/builtin/fsmonitor--daemon.c
> +++ b/builtin/fsmonitor--daemon.c
> @@ -1209,7 +1209,7 @@ static int fsmonitor_run_daemon_1(struct fsmonitor_daemon_state *state)
>  	 * events.
>  	 */
>  	if (pthread_create(&state->listener_thread, NULL,
> -			   fsm_listen__thread_proc, state) < 0) {
> +			   fsm_listen__thread_proc, state)) {
>  		ipc_server_stop_async(state->ipc_server_data);
>  		err = error(_("could not start fsmonitor listener thread"));
>  		goto cleanup;
> @@ -1220,7 +1220,7 @@ static int fsmonitor_run_daemon_1(struct fsmonitor_daemon_state *state)
>  	 * Start the health thread to watch over our process.
>  	 */
>  	if (pthread_create(&state->health_thread, NULL,
> -			   fsm_health__thread_proc, state) < 0) {
> +			   fsm_health__thread_proc, state)) {
>  		ipc_server_stop_async(state->ipc_server_data);
>  		err = error(_("could not start fsmonitor health thread"));
>  		goto cleanup;
> diff --git a/run-command.c b/run-command.c
> index 48b9ba6d6f0..756f1839aab 100644
> --- a/run-command.c
> +++ b/run-command.c
> @@ -1019,7 +1019,7 @@ static void *run_thread(void *data)
>  		sigset_t mask;
>  		sigemptyset(&mask);
>  		sigaddset(&mask, SIGPIPE);
> -		if (pthread_sigmask(SIG_BLOCK, &mask, NULL) < 0) {
> +		if (pthread_sigmask(SIG_BLOCK, &mask, NULL)) {
>  			ret = error("unable to block SIGPIPE in async thread");
>  			return (void *)ret;
>  		}
>
> base-commit: 805265fcf7a737664a8321aaf4a0587b78435184

This looks good to me, and skimming through the rest of the
pthread_create() it seems the rest of the code in-tree is correct.

But (and especially if you're interested) we really should follow-up
here and fix the "error()" etc. part of this. After this we have cases
in-tree where we on failure:

 * Call die_errno() (good)
 * Call die(), error() etc., but with a manual strerror() argument,
   these should just use the *_errno() helper.
 * Don't report on the errno at all, e.g. in this case shown here.

It seems to me that all of these should be using die_errno(),
error_errno() etc.

Or maybe it's the other way around, and we should not rely on the global
"errno", but always capture the return value, and give that to
strerror() (or set "errno = ret", and call {die,error,warning}_errno()).

In any case, some low-hanging #leftoverbits there...