From: Junio C Hamano <gitster@pobox.com>
Date: Mon, 11 May 2015 18:04:54 GMT
Subject: Re: [PATCH 1/2] lockfile: allow file locking to be retried with a timeout
Message-ID: <xmqq38337zy1.fsf@gitster.dls.corp.google.com>
In-Reply-To: <1430491977-25817-2-git-send-email-mhagger@alum.mit.edu>

Michael Haggerty <mhagger@alum.mit.edu> writes:

> Signed-off-by: Michael Haggerty <mhagger@alum.mit.edu>
> ---
>
> Notes (discussion):
>     It would be easy to also add a hold_lock_file_for_append_timeout(),
>     but I can't yet think of an application for it.
>
>  lockfile.c | 79 ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++--
>  lockfile.h | 16 +++++++++++--
>  2 files changed, 91 insertions(+), 4 deletions(-)
>
> diff --git a/lockfile.c b/lockfile.c
> index 9889277..30e65e9 100644
> --- a/lockfile.c
> +++ b/lockfile.c
> @@ -157,6 +157,80 @@ static int lock_file(struct lock_file *lk, const char *path, int flags)
>  	return lk->fd;
>  }
>  
> +static int sleep_microseconds(long us)
> +{
> +	struct timeval tv;
> +	tv.tv_sec = 0;
> +	tv.tv_usec = us;
> +	return select(0, NULL, NULL, NULL, &tv);
> +}

This is familiar for an old timer like me.  It seems help.c uses
"poll(NULL, 0, timeout)" for "do nothing but wait" (and we have
compat/poll to help those who lack poll() by using select()).

As we do not need microseconds resolution here, either would be fine
;-)