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