| 1 | /* |
| 2 | * timing.c |
| 3 | * |
| 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. |
| 10 | * |
| 11 | * |
| 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. |
| 18 | * |
| 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. |
| 27 | * |
| 28 | */ |
| 29 | |
| 30 | #include <assert.h> |
| 31 | #include <stdio.h> |
| 32 | |
| 33 | #include "putty.h" |
| 34 | #include "tree234.h" |
| 35 | |
| 36 | struct timer { |
| 37 | timer_fn_t fn; |
| 38 | void *ctx; |
| 39 | unsigned long now; |
| 40 | unsigned long when_set; |
| 41 | }; |
| 42 | |
| 43 | static tree234 *timers = NULL; |
| 44 | static tree234 *timer_contexts = NULL; |
| 45 | static unsigned long now = 0L; |
| 46 | |
| 47 | static int compare_timers(void *av, void *bv) |
| 48 | { |
| 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; |
| 53 | |
| 54 | if (at < bt) |
| 55 | return -1; |
| 56 | else if (at > bt) |
| 57 | return +1; |
| 58 | |
| 59 | /* |
| 60 | * Failing that, compare on the other two fields, just so that |
| 61 | * we don't get unwanted equality. |
| 62 | */ |
| 63 | #if defined(__LCC__) || defined(__clang__) |
| 64 | /* lcc won't let us compare function pointers. Legal, but annoying. */ |
| 65 | { |
| 66 | int c = memcmp(&a->fn, &b->fn, sizeof(a->fn)); |
| 67 | if (c) |
| 68 | return c; |
| 69 | } |
| 70 | #else |
| 71 | if (a->fn < b->fn) |
| 72 | return -1; |
| 73 | else if (a->fn > b->fn) |
| 74 | return +1; |
| 75 | #endif |
| 76 | |
| 77 | if (a->ctx < b->ctx) |
| 78 | return -1; |
| 79 | else if (a->ctx > b->ctx) |
| 80 | return +1; |
| 81 | |
| 82 | /* |
| 83 | * Failing _that_, the two entries genuinely are equal, and we |
| 84 | * never have a need to store them separately in the tree. |
| 85 | */ |
| 86 | return 0; |
| 87 | } |
| 88 | |
| 89 | static int compare_timer_contexts(void *av, void *bv) |
| 90 | { |
| 91 | char *a = (char *)av; |
| 92 | char *b = (char *)bv; |
| 93 | if (a < b) |
| 94 | return -1; |
| 95 | else if (a > b) |
| 96 | return +1; |
| 97 | return 0; |
| 98 | } |
| 99 | |
| 100 | static void init_timers(void) |
| 101 | { |
| 102 | if (!timers) { |
| 103 | timers = newtree234(compare_timers); |
| 104 | timer_contexts = newtree234(compare_timer_contexts); |
| 105 | now = GETTICKCOUNT(); |
| 106 | } |
| 107 | } |
| 108 | |
| 109 | unsigned long schedule_timer(int ticks, timer_fn_t fn, void *ctx) |
| 110 | { |
| 111 | unsigned long when; |
| 112 | struct timer *t, *first; |
| 113 | |
| 114 | init_timers(); |
| 115 | |
| 116 | now = GETTICKCOUNT(); |
| 117 | when = ticks + now; |
| 118 | |
| 119 | /* |
| 120 | * Just in case our various defences against timing skew fail |
| 121 | * us: if we try to schedule a timer that's already in the |
| 122 | * past, we instead schedule it for the immediate future. |
| 123 | */ |
| 124 | if (when - now <= 0) |
| 125 | when = now + 1; |
| 126 | |
| 127 | t = snew(struct timer); |
| 128 | t->fn = fn; |
| 129 | t->ctx = ctx; |
| 130 | t->now = when; |
| 131 | t->when_set = now; |
| 132 | |
| 133 | if (t != add234(timers, t)) { |
| 134 | sfree(t); /* identical timer already exists */ |
| 135 | } else { |
| 136 | add234(timer_contexts, t->ctx);/* don't care if this fails */ |
| 137 | } |
| 138 | |
| 139 | first = (struct timer *)index234(timers, 0); |
| 140 | if (first == t) { |
| 141 | /* |
| 142 | * This timer is the very first on the list, so we must |
| 143 | * notify the front end. |
| 144 | */ |
| 145 | timer_change_notify(first->now); |
| 146 | } |
| 147 | |
| 148 | return when; |
| 149 | } |
| 150 | |
| 151 | /* |
| 152 | * Call to run any timers whose time has reached the present. |
| 153 | * Returns the time (in ticks) expected until the next timer after |
| 154 | * that triggers. |
| 155 | */ |
| 156 | int run_timers(unsigned long anow, unsigned long *next) |
| 157 | { |
| 158 | struct timer *first; |
| 159 | |
| 160 | init_timers(); |
| 161 | |
| 162 | now = GETTICKCOUNT(); |
| 163 | |
| 164 | while (1) { |
| 165 | first = (struct timer *)index234(timers, 0); |
| 166 | |
| 167 | if (!first) |
| 168 | return FALSE; /* no timers remaining */ |
| 169 | |
| 170 | if (find234(timer_contexts, first->ctx, NULL) == NULL) { |
| 171 | /* |
| 172 | * This timer belongs to a context that has been |
| 173 | * expired. Delete it without running. |
| 174 | */ |
| 175 | delpos234(timers, 0); |
| 176 | sfree(first); |
| 177 | } else if (now - (first->when_set - 10) > |
| 178 | first->now - (first->when_set - 10)) { |
| 179 | /* |
| 180 | * This timer is active and has reached its running |
| 181 | * time. Run it. |
| 182 | */ |
| 183 | delpos234(timers, 0); |
| 184 | first->fn(first->ctx, first->now); |
| 185 | sfree(first); |
| 186 | } else { |
| 187 | /* |
| 188 | * This is the first still-active timer that is in the |
| 189 | * future. Return how long it has yet to go. |
| 190 | */ |
| 191 | *next = first->now; |
| 192 | return TRUE; |
| 193 | } |
| 194 | } |
| 195 | } |
| 196 | |
| 197 | /* |
| 198 | * Call to expire all timers associated with a given context. |
| 199 | */ |
| 200 | void expire_timer_context(void *ctx) |
| 201 | { |
| 202 | init_timers(); |
| 203 | |
| 204 | /* |
| 205 | * We don't bother to check the return value; if the context |
| 206 | * already wasn't in the tree (presumably because no timers |
| 207 | * ever actually got scheduled for it) then that's fine and we |
| 208 | * simply don't need to do anything. |
| 209 | */ |
| 210 | del234(timer_contexts, ctx); |
| 211 | } |