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g_timeout_*_seconds: don't overflow for large intervals

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Previously, the `guint interval` parameter, measured in seconds, was
multiplied by 1000 and stored in another `guint` field. For intervals
greater than (G_MAXUINT / 1000) seconds, this would overflow; the
timeout would fire much sooner than intended.

Since GTimeoutSource already keeps track of whether it was created at
millisecond or second resolution, always store the passed interval
directly. We later convert the interval to microseconds, stored in a
gint64, so can move the `* 1000` to there.

The eagle-eyed reader might notice that there is no obvious guarantee
that the source's expiration time in microseconds won't overflow the
gint64, but I don't think this is a new problem. Previously, the
monotonic time would have to reach (2 ** 63 - 2 ** 32) microseconds for
this overflow to occur; now it would have to reach approximately (2 **
63 - 2 ** 42) microseconds. Both of these are 292.47 millennia to 5
significant figures.

Fixes #1600.
This commit is contained in:
Will Thompson 2018-11-26 16:04:10 +00:00
parent 6debbbfd73
commit 4ff3734ff5
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GPG Key ID: 3422DC0D7AD482A7
1 changed files with 8 additions and 3 deletions
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11
glib/gmain.c
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@ -315,6 +315,7 @@ struct _GMainLoop
struct _GTimeoutSource
{
GSource source;
/* Measured in seconds if 'seconds' is TRUE, or milliseconds otherwise. */
guint interval;
gboolean seconds;
};
@ -4615,8 +4616,6 @@ g_timeout_set_expiration (GTimeoutSource *timeout_source,
{
gint64 expiration;
expiration = current_time + (guint64) timeout_source->interval * 1000;
if (timeout_source->seconds)
{
gint64 remainder;
@ -4638,6 +4637,8 @@ g_timeout_set_expiration (GTimeoutSource *timeout_source,
timer_perturb = 0;
}
expiration = current_time + (guint64) timeout_source->interval * 1000 * 1000;
/* We want the microseconds part of the timeout to land on the
* 'timer_perturb' mark, but we need to make sure we don't try to
* set the timeout in the past. We do this by ensuring that we
@ -4653,6 +4654,10 @@ g_timeout_set_expiration (GTimeoutSource *timeout_source,
expiration -= remainder;
expiration += timer_perturb;
}
else
{
expiration = current_time + (guint64) timeout_source->interval * 1000;
}
g_source_set_ready_time ((GSource *) timeout_source, expiration);
}
@ -4735,7 +4740,7 @@ g_timeout_source_new_seconds (guint interval)
GSource *source = g_source_new (&g_timeout_funcs, sizeof (GTimeoutSource));
GTimeoutSource *timeout_source = (GTimeoutSource *)source;
timeout_source->interval = 1000 * interval;
timeout_source->interval = interval;
timeout_source->seconds = TRUE;
g_timeout_set_expiration (timeout_source, g_get_monotonic_time ());