4 * This module tracks any timers set up by schedule_timer(). It
5 * keeps all the currently active timers in a list; it informs the
6 * front end of when the next timer is due to go off if that
7 * changes; and, very importantly, it tracks the context pointers
8 * passed to schedule_timer(), so that if a context is freed all
9 * the timers associated with it can be immediately annulled.
12 * The problem is that computer clocks aren't perfectly accurate.
13 * The GETTICKCOUNT function returns a 32bit number that normally
14 * increases by about 1000 every second. On windows this uses the PC's
15 * interrupt timer and so is only accurate to around 20ppm. On unix it's
16 * a value that's calculated from the current UTC time and so is in theory
17 * accurate in the long term but may jitter and jump in the short term.
19 * What PuTTY needs from these timers is simply a way of delaying the
20 * calling of a function for a little while, if it's occasionally called a
21 * little early or late that's not a problem. So to protect against clock
22 * jumps schedule_timer records the time that it was called in the timer
23 * structure. With this information the run_timers function can see when
24 * the current GETTICKCOUNT value is after the time the event should be
25 * fired OR before the time it was set. In the latter case the clock must
26 * have jumped, the former is (probably) just the normal passage of time.
43 static tree234 *timers = NULL;
44 static tree234 *timer_contexts = NULL;
47 static int compare_timers(void *av, void *bv)
49 struct timer *a = (struct timer *)av;
50 struct timer *b = (struct timer *)bv;
51 long at = a->now - now;
52 long bt = b->now - now;
60 * Failing that, compare on the other two fields, just so that
61 * we don't get unwanted equality.
64 /* lcc won't let us compare function pointers. Legal, but annoying. */
66 int c = memcmp(&a->fn, &b->fn, sizeof(a->fn));
75 else if (a->fn > b->fn)
81 else if (a->ctx > b->ctx)
85 * Failing _that_, the two entries genuinely are equal, and we
86 * never have a need to store them separately in the tree.
91 static int compare_timer_contexts(void *av, void *bv)
102 static void init_timers(void)
105 timers = newtree234(compare_timers);
106 timer_contexts = newtree234(compare_timer_contexts);
107 now = GETTICKCOUNT();
111 long schedule_timer(int ticks, timer_fn_t fn, void *ctx)
114 struct timer *t, *first;
118 now = GETTICKCOUNT();
122 * Just in case our various defences against timing skew fail
123 * us: if we try to schedule a timer that's already in the
124 * past, we instead schedule it for the immediate future.
129 t = snew(struct timer);
135 if (t != add234(timers, t)) {
136 sfree(t); /* identical timer already exists */
138 add234(timer_contexts, t->ctx);/* don't care if this fails */
141 first = (struct timer *)index234(timers, 0);
144 * This timer is the very first on the list, so we must
145 * notify the front end.
147 timer_change_notify(first->now);
154 * Call to run any timers whose time has reached the present.
155 * Returns the time (in ticks) expected until the next timer after
158 int run_timers(long anow, long *next)
164 now = GETTICKCOUNT();
167 first = (struct timer *)index234(timers, 0);
170 return FALSE; /* no timers remaining */
172 if (find234(timer_contexts, first->ctx, NULL) == NULL) {
174 * This timer belongs to a context that has been
175 * expired. Delete it without running.
177 delpos234(timers, 0);
179 } else if (first->now - now <= 0 ||
180 now - (first->when_set - 10) < 0) {
182 * This timer is active and has reached its running
185 delpos234(timers, 0);
186 first->fn(first->ctx, first->now);
190 * This is the first still-active timer that is in the
191 * future. Return how long it has yet to go.
200 * Call to expire all timers associated with a given context.
202 void expire_timer_context(void *ctx)
207 * We don't bother to check the return value; if the context
208 * already wasn't in the tree (presumably because no timers
209 * ever actually got scheduled for it) then that's fine and we
210 * simply don't need to do anything.
212 del234(timer_contexts, ctx);