/* The most recent elapsed time, calculated by wtimer_elapsed().
Measured in milliseconds. */
- long elapsed_last;
+ double elapsed_last;
/* Approximately, the time elapsed between the true start of the
measurement and the time represented by START. */
- long elapsed_pre_start;
+ double elapsed_pre_start;
};
/* Allocate a timer. It is not legal to do anything with a freshly
#endif
#ifdef TIMER_WINDOWS
+ /* We use GetSystemTime to get the elapsed time. MSDN warns that
+ system clock adjustments can skew the output of GetSystemTime
+ when used as a timer and gives preference to GetTickCount and
+ high-resolution timers. But GetTickCount can overflow, and hires
+ timers are typically used for profiling, not for regular time
+ measurement. Since we handle clock skew anyway, we just use
+ GetSystemTime. */
FILETIME ft;
SYSTEMTIME st;
GetSystemTime (&st);
+
+ /* As recommended by MSDN, we convert SYSTEMTIME to FILETIME, copy
+ FILETIME to ULARGE_INTEGER, and use regular 64-bit integer
+ arithmetic on that. */
SystemTimeToFileTime (&st, &ft);
wst->HighPart = ft.dwHighDateTime;
wst->LowPart = ft.dwLowDateTime;
wt->elapsed_pre_start = 0;
}
-static long
+static double
wtimer_sys_diff (wget_sys_time *wst1, wget_sys_time *wst2)
{
#ifdef TIMER_GETTIMEOFDAY
- return ((wst1->tv_sec - wst2->tv_sec) * 1000
- + (wst1->tv_usec - wst2->tv_usec) / 1000);
+ return ((double)(wst1->tv_sec - wst2->tv_sec) * 1000
+ + (double)(wst1->tv_usec - wst2->tv_usec) / 1000);
#endif
#ifdef TIMER_TIME
#endif
#ifdef WINDOWS
- return (long)(wst1->QuadPart - wst2->QuadPart) / 10000;
+ return (double)(wst1->QuadPart - wst2->QuadPart) / 10000;
#endif
}
/* Return the number of milliseconds elapsed since the timer was last
reset. It is allowed to call this function more than once to get
- increasingly higher elapsed values. */
+ increasingly higher elapsed values. These timers handle clock
+ skew. */
-long
+double
wtimer_elapsed (struct wget_timer *wt)
{
wget_sys_time now;
- long elapsed;
+ double elapsed;
wtimer_sys_set (&now);
elapsed = wt->elapsed_pre_start + wtimer_sys_diff (&now, &wt->start);
return elapsed;
}
-/* Return the assessed granularity of the timer implementation. This
- is important for certain code that tries to deal with "zero" time
- intervals. */
+/* Return the assessed granularity of the timer implementation, in
+ milliseconds. This is used by code that tries to substitute a
+ better value for timers that have returned zero. */
-long
+double
wtimer_granularity (void)
{
#ifdef TIMER_GETTIMEOFDAY
- /* Granularity of gettimeofday is hugely architecture-dependent.
- However, it appears that on modern machines it is better than
- 1ms. */
- return 1;
+ /* Granularity of gettimeofday varies wildly between architectures.
+ However, it appears that on modern machines it tends to be better
+ than 1ms. Assume 100 usecs. (Perhaps the configure process
+ could actually measure this?) */
+ return 0.1;
#endif
#ifdef TIMER_TIME
#endif
#ifdef TIMER_WINDOWS
- /* ? */
+ /* According to MSDN, GetSystemTime returns a broken-down time
+ structure the smallest member of which are milliseconds. */
return 1;
#endif
}