[pacman-dev] [PATCHv2] use monotonic clock for progress updates

[Dave Reisner]

On Sat, Jun 28, 2014 at 12:07:03PM -0400, Andrew Gregory wrote:
> gettimeofday is susceptible to system time adjustments, skewing or
> altogether breaking progress output.  For the sake of platforms that
> lack clock_gettime support, gettimeofday is retained as a fallback.

Note that CLOCK_MONOTONIC is still susceptible to skew from adjtime
(called by {S,}NTP).

> Fixes FS#36983
> 
> Signed-off-by: Andrew Gregory <andrew.gregory.8 at gmail.com>
> ---
>  src/pacman/callback.c | 61 ++++++++++++++++++++++++++++++++-------------------
>  1 file changed, 38 insertions(+), 23 deletions(-)
> 
> diff --git a/src/pacman/callback.c b/src/pacman/callback.c
> index 9cde1de..dafaeaf 100644
> --- a/src/pacman/callback.c
> +++ b/src/pacman/callback.c
> @@ -21,7 +21,6 @@
>  #include <stdio.h>
>  #include <stdlib.h>
>  #include <string.h>
> -#include <sys/time.h>
>  #include <sys/types.h> /* off_t */
>  #include <time.h>
>  #include <unistd.h>
> @@ -47,6 +46,33 @@ static alpm_list_t *output = NULL;
>  /* update speed for the fill_progress based functions */
>  #define UPDATE_SPEED_MS 200
>  
> +#if defined(CLOCK_MONOTONIC) && defined(_POSIX_MONOTONIC_CLOCK)
> +
> +static void get_time(struct timespec *ts)
> +{
> +	clock_gettime(CLOCK_MONOTONIC, ts);
> +}
> +
> +#else
> +
> +/* darwin doesn't support clock_gettime, fallback to gettimeofday */
> +#include <sys/time.h>
> +static void get_time(struct timespec *ts)

This var is forever unused and will likely throw a compile-time error
with our flags. Is there any case where we ever actually care about the
underlying struct? Why not just return an int64_t or double, e.g.

https://github.com/falconindy/pkgfile/blob/master/src/update.c#L53

> +{
> +	struct timeval tv;
> +	gettimeofday(&tv, NULL);
> +	ts->tv_sec = tv->tv_sec;
> +	ts->tv_nsec = tv->tv_usec * 1000;
> +}
> +
> +#endif
> +
> +static long diff_timespec_ms(struct timespec *t1, struct timespec *t0) {
> +		time_t diff_sec = t1->tv_sec - t0->tv_sec;
> +		long diff_nsec = t1->tv_nsec - t0->tv_nsec;
> +		return (diff_sec * 1000) + (diff_nsec / 1000000);
> +}
> +
>  /**
>   * Silly little helper function, determines if the caller needs a visual update
>   * since the last time this function was called.
> @@ -57,24 +83,18 @@ static alpm_list_t *output = NULL;
>  static long get_update_timediff(int first_call)
>  {
>  	long retval = 0;
> -	static struct timeval last_time = {0, 0};
> +	static struct timespec last_time = {0, 0};
>  
>  	/* on first call, simply set the last time and return */
>  	if(first_call) {
> -		gettimeofday(&last_time, NULL);
> +		get_time(&last_time);
>  	} else {
> -		struct timeval this_time;
> -		time_t diff_sec;
> -		suseconds_t diff_usec;
> -
> -		gettimeofday(&this_time, NULL);
> -		diff_sec = this_time.tv_sec - last_time.tv_sec;
> -		diff_usec = this_time.tv_usec - last_time.tv_usec;
> -
> -		retval = (diff_sec * 1000) + (diff_usec / 1000);
> +		struct timespec this_time;
> +		get_time(&this_time);
> +		retval = diff_timespec_ms(&this_time, &last_time);
>  
>  		/* do not update last_time if interval was too short */
> -		if(retval >= UPDATE_SPEED_MS) {
> +		if(retval < 0 || retval >= UPDATE_SPEED_MS) {
>  			last_time = this_time;
>  		}
>  	}
> @@ -647,7 +667,7 @@ void cb_dl_progress(const char *filename, off_t file_xfered, off_t file_total)
>  {
>  	static double rate_last;
>  	static off_t xfered_last;
> -	static struct timeval initial_time;
> +	static struct timespec initial_time;
>  	int infolen;
>  	int filenamelen;
>  	char *fname, *p;
> @@ -709,21 +729,16 @@ void cb_dl_progress(const char *filename, off_t file_xfered, off_t file_total)
>  		/* set default starting values, ensure we only call this once
>  		 * if TotalDownload is enabled */
>  		if(!totaldownload || (totaldownload && list_xfered == 0)) {
> -			gettimeofday(&initial_time, NULL);
> +			get_time(&initial_time);
>  			xfered_last = (off_t)0;
>  			rate_last = 0.0;
>  			get_update_timediff(1);
>  		}
>  	} else if(file_xfered == file_total) {
>  		/* compute final values */
> -		struct timeval current_time;
> -		time_t diff_sec;
> -		suseconds_t diff_usec;
> -
> -		gettimeofday(&current_time, NULL);
> -		diff_sec = current_time.tv_sec - initial_time.tv_sec;
> -		diff_usec = current_time.tv_usec - initial_time.tv_usec;
> -		timediff = (diff_sec * 1000) + (diff_usec / 1000);
> +		struct timespec current_time;
> +		get_time(&current_time);
> +		timediff = diff_timespec_ms(&current_time, &initial_time);
>  		if(timediff > 0) {
>  			rate = (double)xfered / (timediff / 1000.0);
>  			/* round elapsed time (in ms) to the nearest second */
> -- 
> 2.0.1
> 
>