* 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>
struct timer {
timer_fn_t fn;
void *ctx;
- long now;
+ unsigned long now;
+ unsigned long when_set;
};
static tree234 *timers = NULL;
-static long now = 0L;
+static tree234 *timer_contexts = NULL;
+static unsigned long now = 0L;
static int compare_timers(void *av, void *bv)
{
* Failing that, compare on the other two fields, just so that
* we don't get unwanted equality.
*/
-#ifdef __LCC__
+#if defined(__LCC__) || defined(__clang__)
/* lcc won't let us compare function pointers. Legal, but annoying. */
{
int c = memcmp(&a->fn, &b->fn, sizeof(a->fn));
- if (c < 0)
- return -1;
- else if (c > 0)
- return +1;
+ if (c)
+ return c;
}
#else
if (a->fn < b->fn)
static int compare_timer_contexts(void *av, void *bv)
{
- struct timer *at = (struct timer *)av;
- struct timer *bt = (struct timer *)bv;
- char *a = (char *)at->ctx;
- char *b = (char *)bt->ctx;
+ char *a = (char *)av;
+ char *b = (char *)bv;
if (a < b)
return -1;
else if (a > b)
{
if (!timers) {
timers = newtree234(compare_timers);
+ timer_contexts = newtree234(compare_timer_contexts);
now = GETTICKCOUNT();
}
}
-long schedule_timer(int ticks, timer_fn_t fn, void *ctx)
+unsigned long schedule_timer(int ticks, timer_fn_t fn, void *ctx)
{
- long when;
+ unsigned long when;
struct timer *t, *first;
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 */
+ } else {
+ add234(timer_contexts, t->ctx);/* don't care if this fails */
}
first = (struct timer *)index234(timers, 0);
* Returns the time (in ticks) expected until the next timer after
* that triggers.
*/
-int run_timers(long anow, long *next)
+int run_timers(unsigned long anow, unsigned long *next)
{
struct timer *first;
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);
if (!first)
return FALSE; /* no timers remaining */
- if (first->now - now <= 0) {
+ if (find234(timer_contexts, first->ctx, NULL) == NULL) {
+ /*
+ * This timer belongs to a context that has been
+ * expired. Delete it without running.
+ */
+ delpos234(timers, 0);
+ sfree(first);
+ } else if (now - (first->when_set - 10) >
+ first->now - (first->when_set - 10)) {
/*
* This timer is active and has reached its running
* time. Run it.
*/
void expire_timer_context(void *ctx)
{
- struct timer *ptr;
- struct timer exemplar;
-
- if (!timers) return;
-
- exemplar.ctx = ctx;
- /* don't care about initialisation of other members */
-
- /* Dispose of all timers with this context */
- while ((ptr = (struct timer *)find234(timers, &exemplar,
- compare_timer_contexts))) {
- del234(timers, ptr);
- sfree(ptr);
- }
+ init_timers();
- /* Dispose of timer tree itself if none are left */
- if (count234(timers) == 0) {
- freetree234(timers);
- timers = NULL;
- }
+ /*
+ * We don't bother to check the return value; if the context
+ * already wasn't in the tree (presumably because no timers
+ * ever actually got scheduled for it) then that's fine and we
+ * simply don't need to do anything.
+ */
+ del234(timer_contexts, ctx);
}
projects / u / mdw / putty / blobdiff