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win32: Make g_get_monotonic_clock lockless

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This commit is contained in:
Alexander Larsson 2011-11-04 16:45:41 +01:00
parent 8d023c2706
commit 3a7960f757
1 changed files with 20 additions and 12 deletions
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32
glib/gmain.c
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@ -1974,10 +1974,9 @@ g_get_real_time (void)
}
#ifdef G_OS_WIN32
G_LOCK_DEFINE_STATIC (g_win32_clock);
static ULONGLONG (*g_GetTickCount64) (void) = NULL;
static guint32 g_win32_last_ticks32 = 0;
static guint32 g_win32_tick_epoch = 0;
G_GNUC_INTERNAL void
g_clock_win32_init (void)
{
@ -1987,7 +1986,7 @@ g_clock_win32_init (void)
kernel32 = GetModuleHandle ("KERNEL32.DLL");
if (kernel32 != NULL)
g_GetTickCount64 = (void *) GetProcAddress (kernel32, "GetTickCount64");
g_win32_last_ticks32 = GetTickCount();
g_win32_tick_epoch = ((guint32)GetTickCount()) >> 31;
}
#endif
@ -2126,26 +2125,35 @@ g_get_monotonic_time (void)
}
else
{
G_LOCK (g_win32_clock);
guint32 epoch;
epoch = g_atomic_int_get (&g_win32_tick_epoch);
/* Must read ticks after the epoch, then we're guaranteed
that the ticks value we read is higher or equal to any
previous ones that lead to the writing of the epoch. */
ticks32 = timeGetTime();
/* We have wrapped the 32bit counter, increase the epoch.
/* We store the msb of the current time as the lsb
* of the epoch. Comparing these bits lets us detect when
* the 32bit counter has wrapped so we can increase the
* epoch.
* This will work as long as this function is called at
* least once every ~50 days, which is the wrap time of
* a 32bit msec counter. I think this is pretty likely.
* least once every ~24 days, which is half the wrap time
* of a 32bit msec counter. I think this is pretty likely.
*
* Note that g_win32_tick_epoch is a process local state,
* so the monotonic clock will not be the same between
* processes.
*/
if (ticks32 < g_win32_last_ticks32)
g_win32_tick_epoch++;
if ((ticks32 >> 31) != (epoch & 1))
{
epoch++;
g_atomic_int_set (&g_win32_tick_epoch, epoch);
}
ticks = (guint64)ticks32 | ((guint64)g_win32_tick_epoch) << 32;
g_win32_last_ticks32 = ticks32;
G_UNLOCK (g_win32_clock);
ticks = (guint64)ticks32 | ((guint64)epoch) << 31;
}
return ticks * 1000;