Subject: Re: [PATCH mh/lockfile-retry] lockfile: replace random() by rand()

From: Junio C Hamano <[email-masked]>
Date: Sat, 30 May 2015 10:12:57 -0700

Johannes Sixt <[email-masked]> writes:

> There you have it: Look the other way for a while, and people start
> using exotic stuff... ;)

Is it exotic to have random/srandom?  Both are in POSIX and 4BSD;
admittedly rand/srand are written down in C89 and later, so they
might be more portable, but I recall the prevailing wisdom is to
favor random over rand for quality of randomness and portability, so
I am wondering if it may be a better approach to keep the code as-is
and do a compat/random.c based on either rand/srand (or use posix
sample implementation [*1*]).

[Reference]

*1* http://pubs.opengroup.org/onlinepubs/9699919799/functions/rand.html

>
> This is a build breakage of master on Windows. There are also a few
> new test suite failures. On of them is in t1404#2, indicating that
> a DF conflict takes a different error path. I haven't debugged, yet.
> The lock file retry test fails, too. I'll report back as time permits.
>
>  lockfile.c | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
>
> diff --git a/lockfile.c b/lockfile.c
> index 5a93bc7..ee5cb01 100644
> --- a/lockfile.c
> +++ b/lockfile.c
> @@ -191,7 +191,7 @@ static int lock_file_timeout(struct lock_file *lk, const char *path,
>  		return lock_file(lk, path, flags);
>  
>  	if (!random_initialized) {
> -		srandom((unsigned int)getpid());
> +		srand((unsigned int)getpid());
>  		random_initialized = 1;
>  	}
>  
> @@ -218,7 +218,7 @@ static int lock_file_timeout(struct lock_file *lk, const char *path,
>  
>  		backoff_ms = multiplier * INITIAL_BACKOFF_MS;
>  		/* back off for between 0.75*backoff_ms and 1.25*backoff_ms */
> -		wait_us = (750 + random() % 500) * backoff_ms;
> +		wait_us = (750 + rand() % 500) * backoff_ms;
>  		sleep_microseconds(wait_us);
>  		remaining_us -= wait_us;