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/*
* timing.c
*
* This module tracks any timers set up by schedule_timer(). It
* keeps all the currently active timers in a list; it informs the
* front end of when the next timer is due to go off if that
* 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>
#include <stdio.h>
#include "putty.h"
#include "tree234.h"
struct timer {
timer_fn_t fn;
void *ctx;
unsigned long now;
unsigned long when_set;
};
static tree234 *timers = NULL;
static tree234 *timer_contexts = NULL;
static unsigned long now = 0L;
static int compare_timers(void *av, void *bv)
{
struct timer *a = (struct timer *)av;
struct timer *b = (struct timer *)bv;
long at = a->now - now;
long bt = b->now - now;
if (at < bt)
return -1;
else if (at > bt)
return +1;
/*
* Failing that, compare on the other two fields, just so that
* we don't get unwanted equality.
*/
#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)
return c;
}
#else
if (a->fn < b->fn)
return -1;
else if (a->fn > b->fn)
return +1;
#endif
if (a->ctx < b->ctx)
return -1;
else if (a->ctx > b->ctx)
return +1;
/*
* Failing _that_, the two entries genuinely are equal, and we
* never have a need to store them separately in the tree.
*/
return 0;
}
static int compare_timer_contexts(void *av, void *bv)
{
char *a = (char *)av;
char *b = (char *)bv;
if (a < b)
return -1;
else if (a > b)
return +1;
return 0;
}
static void init_timers(void)
{
if (!timers) {
timers = newtree234(compare_timers);
timer_contexts = newtree234(compare_timer_contexts);
now = GETTICKCOUNT();
}
}
unsigned long schedule_timer(int ticks, timer_fn_t fn, void *ctx)
{
unsigned long when;
struct timer *t, *first;
init_timers();
now = GETTICKCOUNT();
when = ticks + now;
/*
* Just in case our various defences against timing skew fail
* us: if we try to schedule a timer that's already in the
* past, we instead schedule it for the immediate future.
*/
if (when - now <= 0)
when = now + 1;
t = snew(struct timer);
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);
if (first == t) {
/*
* This timer is the very first on the list, so we must
* notify the front end.
*/
timer_change_notify(first->now);
}
return when;
}
/*
* Call to run any timers whose time has reached the present.
* Returns the time (in ticks) expected until the next timer after
* that triggers.
*/
int run_timers(unsigned long anow, unsigned long *next)
{
struct timer *first;
init_timers();
now = GETTICKCOUNT();
while (1) {
first = (struct timer *)index234(timers, 0);
if (!first)
return FALSE; /* no timers remaining */
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.
*/
delpos234(timers, 0);
first->fn(first->ctx, first->now);
sfree(first);
} else {
/*
* This is the first still-active timer that is in the
* future. Return how long it has yet to go.
*/
*next = first->now;
return TRUE;
}
}
}
/*
* Call to expire all timers associated with a given context.
*/
void expire_timer_context(void *ctx)
{
init_timers();
/*
* 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);
}