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

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Am 30.05.2015 um 19:12 schrieb Junio C Hamano:
Johannes Sixt <j6t@xxxxxxxx> 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*]).

For our purposes here, the linear congruence of rand() is certainly sufficient. At this time, compatibility functions for random/srandom would just mean a lot of work for little gain.



[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;


-- Hannes

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