* changes; and, very importantly, it tracks the context pointers
* passed to schedule_timer(), so that if a context is freed all
* the timers associated with it can be immediately annulled.
+ *
+ *
+ * The problem is that computer clocks aren't perfectly accurate.
+ * The GETTICKCOUNT function returns a 32bit number that normally
+ * increases by about 1000 every second. On windows this uses the PC's
+ * interrupt timer and so is only accurate to around 20ppm. On unix it's
+ * a value that's calculated from the current UTC time and so is in theory
+ * accurate in the long term but may jitter and jump in the short term.
+ *
+ * What PuTTY needs from these timers is simply a way of delaying the
+ * calling of a function for a little while, if it's occasionally called a
+ * little early or late that's not a problem. So to protect against clock
+ * jumps schedule_timer records the time that it was called in the timer
+ * structure. With this information the run_timers function can see when
+ * the current GETTICKCOUNT value is after the time the event should be
+ * fired OR before the time it was set. In the latter case the clock must
+ * have jumped, the former is (probably) just the normal passage of time.
+ *
*/
#include <assert.h>
timer_fn_t fn;
void *ctx;
long now;
+ long when_set;
};
static tree234 *timers = NULL;
init_timers();
- when = ticks + GETTICKCOUNT();
+ now = GETTICKCOUNT();
+ when = ticks + now;
/*
* Just in case our various defences against timing skew fail
t->fn = fn;
t->ctx = ctx;
t->now = when;
+ t->when_set = now;
if (t != add234(timers, t)) {
sfree(t); /* identical timer already exists */
init_timers();
-#ifdef TIMING_SYNC
- /*
- * In this ifdef I put some code which deals with the
- * possibility that `anow' disagrees with GETTICKCOUNT by a
- * significant margin. Our strategy for dealing with it differs
- * depending on platform, because on some platforms
- * GETTICKCOUNT is more likely to be right whereas on others
- * `anow' is a better gold standard.
- */
- {
- long tnow = GETTICKCOUNT();
-
- if (tnow + TICKSPERSEC/50 - anow < 0 ||
- anow + TICKSPERSEC/50 - tnow < 0
- ) {
-#if defined TIMING_SYNC_ANOW
- /*
- * If anow is accurate and the tick count is wrong,
- * this is likely to be because the tick count is
- * derived from the system clock which has changed (as
- * can occur on Unix). Therefore, we resolve this by
- * inventing an offset which is used to adjust all
- * future output from GETTICKCOUNT.
- *
- * A platform which defines TIMING_SYNC_ANOW is
- * expected to have also defined this offset variable
- * in (its platform-specific adjunct to) putty.h.
- * Therefore we can simply reference it here and assume
- * that it will exist.
- */
- tickcount_offset += anow - tnow;
-#elif defined TIMING_SYNC_TICKCOUNT
- /*
- * If the tick count is more likely to be accurate, we
- * simply use that as our time value, which may mean we
- * run no timers in this call (because we got called
- * early), or alternatively it may mean we run lots of
- * timers in a hurry because we were called late.
- */
- anow = tnow;
-#else
-/*
- * Any platform which defines TIMING_SYNC must also define one of the two
- * auxiliary symbols TIMING_SYNC_ANOW and TIMING_SYNC_TICKCOUNT, to
- * indicate which measurement to trust when the two disagree.
- */
-#error TIMING_SYNC definition incomplete
-#endif
- }
- }
-#endif
-
- now = anow;
+ now = GETTICKCOUNT();
while (1) {
first = (struct timer *)index234(timers, 0);
*/
delpos234(timers, 0);
sfree(first);
- } else if (first->now - now <= 0) {
+ } else if (first->now - now <= 0 ||
+ now - (first->when_set - 10) < 0) {
/*
* This timer is active and has reached its running
* time. Run it.
ret = select(maxfd, &rset, &wset, &xset, ptv);
if (ret == 0)
now = next;
- else {
- long newnow = GETTICKCOUNT();
- /*
- * Check to see whether the system clock has
- * changed massively during the select.
- */
- if (newnow - now < 0 || newnow - now > next - now) {
- /*
- * If so, look at the elapsed time in the
- * select and use it to compute a new
- * tickcount_offset.
- */
- long othernow = now + tv.tv_sec * 1000 + tv.tv_usec / 1000;
- /* So we'd like GETTICKCOUNT to have returned othernow,
- * but instead it return newnow. Hence ... */
- tickcount_offset += othernow - newnow;
- now = othernow;
- } else {
- now = newnow;
- }
- }
+ else
+ now = GETTICKCOUNT();
} while (ret < 0 && errno == EINTR);
if (ret < 0) {
ret = select(maxfd, &rset, &wset, &xset, ptv);
if (ret == 0)
now = next;
- else {
- long newnow = GETTICKCOUNT();
- /*
- * Check to see whether the system clock has
- * changed massively during the select.
- */
- if (newnow - now < 0 || newnow - now > next - now) {
- /*
- * If so, look at the elapsed time in the
- * select and use it to compute a new
- * tickcount_offset.
- */
- long othernow = now + tv.tv_sec * 1000 + tv.tv_usec / 1000;
- /* So we'd like GETTICKCOUNT to have returned othernow,
- * but instead it return newnow. Hence ... */
- tickcount_offset += othernow - newnow;
- now = othernow;
- } else {
- now = newnow;
- }
- }
+ else
+ now = GETTICKCOUNT();
} while (ret < 0 && errno != EINTR);
} while (ret == 0);
projects / u / mdw / putty / commitdiff