patchlockfile: replace random() by rand()

>
> 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;

> Johannes Sixt <j6t@kdbg.org> 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;
>

> Am 30.05.2015 um 19:12 schrieb Junio C Hamano:
>> Johannes Sixt <j6t@kdbg.org> 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.

> On 06/04/2015 10:40 AM, Johannes Sixt wrote:
> We *certainly* don't require high-quality random numbers for this
> application. Regarding portability, there is one definite point in favor
> of rand() (it's available on Windows) vs. Junio's recollection that
> random() might have portability advantages, presumably on other platforms.

>
> Johannes Sixt (4):
>   lockfile: replace random() by rand()
>   help.c: wrap wait-only poll() invocation in sleep_millisec()
>   lockfile: convert retry timeout computations to millisecond
>   lockfile: wait using sleep_millisec() instead of select()
>
>  cache.h    |  1 +
>  help.c     |  2 +-
>  lockfile.c | 31 +++++++++----------------------
>  wrapper.c  |  5 +++++
>  4 files changed, 16 insertions(+), 23 deletions(-)

> The first patch is the same that I posted earlier. It fixes a build
> failure on Windows on master due to missing random/srandom.
> 
> The remaining 3 patches replace the select() invocation that waits
> for a short time period by the version with poll() that we already
> use in help.c. This is necessary because a select() call where all
> three sets of file descriptors are empty is not supported on Windows.
> 
> Johannes Sixt (4):
>   lockfile: replace random() by rand()
>   help.c: wrap wait-only poll() invocation in sleep_millisec()
>   lockfile: convert retry timeout computations to millisecond
>   lockfile: wait using sleep_millisec() instead of select()
> 
>  cache.h    |  1 +
>  help.c     |  2 +-
>  lockfile.c | 31 +++++++++----------------------
>  wrapper.c  |  5 +++++
>  4 files changed, 16 insertions(+), 23 deletions(-)